View source for 86-DOS

{{Short description|Computer operating system}}
{{Use dmy dates|date=May 2019|cs1-dates=y}}
{{Use list-defined references|date=December 2021}}
{{Infobox OS
| name = 86-DOS
| logo = 86-DOS logo.svg
| screenshot = 86-DOS running assembler and HEX2BIN (screenshot).png
| caption = A sample 86-DOS session (simulated)
| developer = [[Seattle Computer Products]]&nbsp;/ [[Tim Paterson]]
| supported_platforms = [[x86]]
| kernel_type = [[Monolithic kernel]]
| influenced_by = [[CP/M]]
| ui = [[Command-line interface]] ([[COMMAND.COM]])
| family = [[DOS]]
| released = {{Start date and age|1980|df=yes}}
| latest_release_version = 86-DOS 1.10
| latest_release_date = {{Start date and age|1981|07|df=yes}}
| marketing_target = [[S-100 bus|S-100]]-based micro-computers with 8086 processor
| programmed_in = [[Intel 8086|8086]] [[assembly language]]
| prog_language = [[Intel 8086|8086]] [[assembly language]]
| language = [[English language|English]]
| updatemodel = 
| package_manager = N/A
| working_state = Historic, unsupported
| license = [[Proprietary software|Proprietary]]
| succeeded by = [[MS-DOS]], [[IBM PC DOS]]
| website = 
}}

'''86-DOS''' (known internally as '''QDOS''',<ref name="Paterson_2019_Presentation">{{cite web |last1=Paterson |first1=Tim |title=The Original DOS and the Old Days |url=https://www.youtube.com/watch?v=R2Qh0O3Dt10 |website=YouTube |publisher=Vintage Computer Federation |access-date=1 March 2022 |location=Mountain View, CA, United States |date=5 August 2018}}</ref> for '''Quick and Dirty Operating System''') is a discontinued [[operating system]] developed and marketed by [[Seattle Computer Products]] (SCP) for its [[Intel 8086]]-based computer kit.

86-DOS shared a few of its commands with other operating systems such as [[OS/8]] and [[CP/M]], which made it easy to [[porting|port]] programs from the latter. Its [[application programming interface]] was very similar to that of CP/M. The system was licensed and then purchased by [[Microsoft]] and developed further as [[MS-DOS]] and [[PC&nbsp;DOS]].<ref name="Beley_1986_MS-DOS_Encyclopedia"/>

==History==
===Origins===
86-DOS was created because sales of the [[Seattle Computer Products]] 8086 [[electronic kit|computer kit]], demonstrated in June 1979 and shipped in November,<ref name="Hunter_1983_Roots_of_DOS"/> were languishing due to the absence of an operating system. The only software that SCP could sell with the board was Microsoft's [[Standalone Disk BASIC-86]], which Microsoft had developed on a prototype of SCP's hardware.<ref name="Hunter_1983_Roots_of_DOS"/> SCP wanted to offer the 8086-version of [[CP/M]] that Digital Research had initially announced for November 1979, but it was delayed and its release date was uncertain.{{r|paterson198306}} This was not the first time Digital Research had lagged behind hardware developments; two years earlier it had been slow to adapt CP/M for new [[floppy disk]] formats and [[hard disk drive]]s. In April 1980, SCP assigned 24-year-old [[Tim Paterson]] to develop a substitute for [[CP/M-86]].<ref name="Hunter_1983_Roots_of_DOS"/>

Using a CP/M-80 manual as reference,<ref name="nerds2"/> Paterson modeled 86-DOS after its architecture and interfaces, but adapted to meet the requirements of Intel's 8086 [[16-bit]] processor, for easy (and partially automated) source-level translatability of the many existing [[8-bit]] CP/M programs;<ref name="paterson198306"/> porting them to either DOS or CP/M-86 was about equally difficult<ref name="edlin19820607"/> and eased by the fact that Intel had already published a method that could be used to automatically translate software from the [[Intel 8080]] processor, for which CP/M had been designed, to the new 8086 instruction set.{{r|paterson198306}} At the same time he made a number of changes and enhancements to address what he saw as CP/M's shortcomings. CP/M [[cache (computing)|cached]] file system information in memory for speed, but this required a user to force an update to a disk before removing it; if the user forgot, the disk would become corrupt. Paterson took the safer, but slower approach of updating the disk with each operation. CP/M's [[Peripheral Interchange Program|PIP]] command, which copied files, supported several special file names that referred to hardware devices such as [[printer (computing)|printers]] and [[Computer port (hardware)|communication ports]]. Paterson built these names into the operating system as [[device file]]s so that any program could use them. He gave his copying program the more intuitive name [[COPY (DOS command)|COPY]]. Rather than implementing [[CP/M#File_system|CP/M's file system]], he drew on Microsoft Standalone Disk BASIC-86's [[File Allocation Table]] (FAT) [[file system]].<ref name="Beley_1986_MS-DOS_Encyclopedia"/>

By mid-1980 SCP advertised 86-DOS, priced at {{currency|amount=95|code=USD|linked=yes}} for owners of its {{currency|amount=1290|code=USD|linked=no}} 8086-board and {{currency|amount=195|code=USD|linked=no}} for others. It touted the software's ability to read [[Zilog Z80]] source code from a CP/M disk and translate it to 8086 source code, and promised that only "minor hand correction and optimization" was needed to produce 8086 binaries.{{r|BYTE_1980_86-DOS}}

===IBM interest===
In October 1980, [[IBM]] was developing what would become the original [[IBM Personal Computer]]. CP/M was by far the most popular operating system in use at the time, and IBM felt that it needed CP/M in order to compete. IBM's representatives visited Digital Research and discussed [[licensing]] with Digital Research's licensing representative, [[Dorothy Kildall]] (née McEwen), who hesitated to sign IBM's [[non-disclosure agreement]]. Although the NDA was later accepted, Digital Research would not accept IBM's proposal of {{currency|amount=250,000|code=USD|linked=no}} in exchange for as many copies as IBM could sell, insisting on the usual [[Royalties|royalty]]-based plan.<ref name="Freiberger_1984_Fire_Valley"/> In later discussions between IBM and [[Bill Gates]], Gates mentioned the existence of 86-DOS, and IBM representative Jack Sams told him to get a license for it.{{citation needed|date=July 2011}}

===Creation of PC&nbsp;DOS===
Microsoft purchased a non-exclusive license for 86-DOS from Seattle Computer Products<ref name="86-DOS_License"/> in December 1980 for {{currency|amount=25000|code=USD|linked=no}}.{{Citation needed|date=April 2013}}<!-- Lots of third-party sources state 1980-12 and US$25,000, however, the license agreement was signed on 1981-01-06 and the total payments described in there depended on some conditions. This needs to be sorted out in better detail. --> In May 1981, it hired Tim Paterson to port the system to the IBM&nbsp;PC,<ref name="Hunter_1983_Roots_of_DOS"/> which used the slower and less expensive [[Intel 8088]] processor and had its own specific family of peripherals. IBM watched the developments daily,<ref name="Hunter_1983_Roots_of_DOS"/> submitting over 300 [[change request]]s before it accepted the product and wrote the user manual for it.

In July 1981, a month before the PC's release, Microsoft purchased all rights to 86-DOS from SCP for {{currency|amount=50000|code=USD|linked=no}}.<ref name="Hunter_1983_Roots_of_DOS"/><ref name="86-DOS_Sale"/><ref name="Duncan_1988_MS-DOS_Encyclopedia"/> It met IBM's main criteria: it looked like CP/M,<ref name="Beley_1986_MS-DOS_Encyclopedia"/> and it was easy to adapt existing 8-bit CP/M programs to run under it, notably thanks to the [[TRANS (command)|TRANS]] command which would translate source files from 8080 to 8086 machine instructions. Microsoft licensed 86-DOS to IBM, and it became PC&nbsp;DOS&nbsp;1.0. This license also permitted Microsoft to sell DOS to other companies, which it did. The deal was spectacularly successful, and SCP later claimed in court that Microsoft had concealed its relationship with IBM in order to purchase the operating system cheaply. SCP ultimately received a {{currency|amount=1|code=USD|linked=no}}&nbsp;million settlement payment.

===Intellectual property dispute===
When Digital Research founder [[Gary Kildall]] examined PC&nbsp;DOS and found that it duplicated CP/M's programming interface, he wanted to sue IBM, which at the time claimed that PC&nbsp;DOS was its own product. However, Digital Research's attorney did not believe that the relevant law was clear enough to sue. Nonetheless, Kildall confronted IBM and persuaded them to offer CP/M-86 with the PC in exchange for a release of liability.

Controversy has continued to surround the similarity between the two systems. Perhaps the most sensational claim came from [[Jerry Pournelle]], who said that Kildall personally demonstrated to him that DOS contained CP/M code by entering a command in DOS that displayed Kildall's name,<ref name="TWIT_2006"/><ref group="nb" name="NB_Paterson_EasterEgg"/> but Pournelle never revealed the command and nobody has come forward to corroborate his story. A 2004 book about Kildall says that he used such an encrypted message to demonstrate that other manufacturers had copied CP/M, but does not say that he found the message in DOS;<ref name="Evans_2004_They_Made_America"/> instead Kildall's memoir (a source for the book) pointed to the well-known interface similarity. Paterson insists that the 86-DOS software was his original work and has denied referring to or otherwise using CP/M code while writing it.<ref name="Paterson_1994_Origins_DOS"/><ref name="Paterson_1997"/> After the 2004 book appeared, he sued the authors and publishers for [[defamation]].<ref name="USA_Today_2005_Programmer_Sues"/> The court ruled in [[summary judgment]] that no defamation had occurred, as the book's claims were opinions based on research or were not provably false.<ref name="Paterson_v_Little_2007"/>

==={{anchor|0.10|0.11|0.20|0.30|0.33|0.34}}{{anchor|0.42|0.56|0.60|0.74|0.75|0.76|0.80|1.00|1.01|1.10}}Versions===
{| class="wikitable"
|-
! {{rh|style=white-space:nowrap;}} | QDOS 0.10<!-- pending zero --> 
| 1980-07<ref name="Hunter_1983_Roots_of_DOS"/> || Roughly half completed version of the OS.<ref name="Hunter_1983_Roots_of_DOS"/> It implemented the original form of Paterson's derivation of Microsoft's [[FAT filesystem]]. In contrast to the earlier [[8-bit FAT]] filesystem found in [[Standalone Disk BASIC-86]], this variant<!-- well, at least 0.3 is known for this --> already supported 12-bit table elements,<ref name="Paterson_2007_Design-DOS"/> reduced the number of FATs from 3<ref name="Schulman_1994_Undocumented-DOS"/> to 2, redefined the semantics of some of the reserved cluster values<!-- according to Marc McDonald in 2012-08 -->, and modified the disk layout, so that the root directory was now located between the FAT and the data area<!-- according to Marc McDonald in 2012-08 -->. Paterson also increased the previous 9-character length limit<!-- in Standalone Disk BASIC-80/86 --> to 11 characters in order to support [[CP/M]]-style [[8.3 filename]]s and [[File Control Block]]s. This variant, however, still used 16-byte directory entries and therefore is not compatible with what became later known as [[FAT12]] in MS-DOS/PC&nbsp;DOS.<!-- and supported since 86-DOS 0.42 --> Possibly shipped already.<ref name="Paterson_1983_Byte_Short_History"/>
|-
! {{rh|style=white-space:nowrap;}} | QDOS/86-DOS 0.11 
| 1980-08
| Bug fix<ref name="Hunter_1983_Roots_of_DOS"/> shipment.<ref name="Hunter_1983_Roots_of_DOS"/><!-- Definitely shipped -->
|-
! {{rh|style=white-space:nowrap;}} | QDOS/86-DOS 0.2 
| 1980-08
| [[EDLIN]] added. Renamed to 86-DOS by August 1980.<ref name="BYTE_1980_86-DOS"/>
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.3<!-- no pending zero --> 
| 15 November 1980 || First version licensed by SCP to Microsoft.<ref name="86-DOS_License"/>
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.33 
| 1980-12
| First version distributed by SCP to [[Original equipment manufacturer|OEM]]s and Microsoft as 86-DOS.<ref name="Hunter_1983_Roots_of_DOS"/><ref name="86-DOS_License"/>
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.34<ref name="Paterson_2014_MSDOS125"/> 
| 29 December 1980<ref name="Paterson_2014_MSDOS125"/> || Cleaned up release for SCP OEMs including Microsoft.
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.42<ref name="Paterson_2014_MSDOS125"/> 
| 25 February 1981<ref name="Paterson_2014_MSDOS125"/> || At the indirect request of IBM (through Microsoft<ref name="86-DOS_Sale"/>) size of directory entries changed from 16 to 32&nbsp;bytes<!-- according to Marc McDonald in 2012-08 --> (similar to [[MIDAS (operating system)|MDOS/MIDAS]]<!-- unknown, if the same layout of 32-byte entries as in MIDAS was used in 86-DOS or not, but both supported 32-byte directory entries -->) in order to add support for a last-modified date stamp (2&nbsp;bytes) and theoretical file sizes larger than 16&nbsp;MB (4&nbsp;bytes)<!-- not sure how it was organized in earlier versions right now, as I'm not sure if earlier versions supported byte-level granular file access already -->,<ref name="SCP_1981_86-DOS_1.0_Addendum"/> thereby implementing the earliest form of the [[12-bit FAT]] file system logically fully compatible with what became known as [[FAT12]] in MS-DOS/PC&nbsp;DOS later on. 86-DOS retained the capability to read volumes written under older versions of 86-DOS up to [[MS-DOS 1.14]] at the least<!-- SCP 86-DOS 1.0 tested, SCP MS-DOS 2.0 not tested yet. SCP MS-DOS 1.25 was thought to support this as well, but now that MS has published the source code (in 2014-03) of what they claim is MS-DOS 1.25, I couldn't find it in there. -->, whereas generic [[MS-DOS 1.20]] / [[PC&nbsp;DOS 1.1]] and higher no longer supported it.<!-- [[PC DOS 1.0]] possibly still supported it, but not tested yet. It is known, that SMALLDIR support was removed for MS-DOS 1.20 / 1981-12-31. -->
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.56<ref name="Paterson_2014_MSDOS125"/> 
| 23 March 1981<ref name="Paterson_2014_MSDOS125"/> || Support for disk blocking/deblocking as requested since 1981-01-15.<ref name="86-DOS_Sale"/>
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.60<ref name="Paterson_2014_MSDOS125"/> 
| 27 March 1981<ref name="Paterson_2014_MSDOS125"/> || The file <code>DOSIO.ASM</code> found in 86-DOS 1.00 mentions that it is the "I/O System for 86-DOS version 0.60 and later".<ref name="86-DOS_Files"/>
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.74<ref name="Paterson_2014_MSDOS125"/> 
| 15 April 1981<ref name="Paterson_2014_MSDOS125"/> || Added [[device file]]s.
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.75<ref name="Paterson_2014_MSDOS125"/> 
| 17 April 1981<ref name="Paterson_2014_MSDOS125"/> || Bug fix.
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.76<ref name="Paterson_2014_MSDOS125"/> 
| 23 April 1981<ref name="Paterson_2014_MSDOS125"/> || Bug fix.
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 0.80<ref name="Paterson_2014_MSDOS125"/> 
| 27 April 1981<ref name="Paterson_2014_MSDOS125"/> || Added system calls.
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 1.00<ref name="Paterson_1983_Byte_Short_History"/><ref name="Paterson_2014_MSDOS125"/> 
| 28 April 1981<ref name="Paterson_2014_MSDOS125"/> || Modified system calls.<ref name="Hunter_1983_Roots_of_DOS"/><ref name="Paterson_1983_Byte_Short_History"/><ref name="86-DOS_Files"/><ref name="SCP_86-DOS_1.0_Files"/>
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 1.01<ref name="Paterson_2014_MSDOS125"/> 
| 12 May 1981<ref name="Paterson_2014_MSDOS125"/> || Bug fix.
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 1.10<ref name="Paterson_2014_MSDOS125"/> 
| 21 July 1981<ref name="Paterson_2014_MSDOS125"/><!-- not a typo here --> || Purchased by Microsoft and renamed to MS-DOS on 27 July 1981,<ref name="86-DOS_Sale"/><ref name="Paterson_1983_Byte_Short_History"/> therefore the last version with genuinely matching 86-DOS and MS-DOS version numbers. First version known to implement the 'hidden' attribute.<!-- not sure when the 'system' attribute support was added, as it was not needed by 86-DOS, but it was supported by PC DOS 1.0 already. -->
|-
! {{rh|style=white-space:nowrap;}} | 86-DOS 1.14<ref name="Paterson_1983_Byte_Short_History"/> 
| 1981-10/11 || According to Tim Paterson [[PC&nbsp;DOS 1.0]] basically reflects 86-DOS 1.14,<ref name="Paterson_1983_Byte_Short_History"/> other sources find a match of PC&nbsp;DOS 1.0 with MS-DOS/86-DOS 1.10 as of 21 July 1981 more likely.
|}

==Features==

===Commands===
The following list of [[command (computing)|commands]] is supported by 86-DOS.<ref name="SCP_1980_86-DOS-UM"/>

====Internal commands====
{{div col|colwidth=9em}}
* CLEAR
* [[COPY (DOS command)|COPY]]
* [[DIR (DOS command)|DIR]]
* [[DEL (DOS command)|ERASE]]
* [[REN (DOS command)|RENAME]]
* [[TYPE (DOS command)|TYPE]]
{{div col end}}

====External commands====
{{div col|colwidth=9em}}
* [[Assembly language#Assembler|ASM]]
* [[CHKDSK]]
* [[DEBUG (DOS command)|DEBUG]]
* [[EDLIN]]
* HEX2BIN
* MAKRDCPM
* RDCPM
* [[SYS (DOS command)|SYS]]
* [[TRANS.COM|TRANS]]
{{div col end}}

=====EDLIN=====
By 1982, when IBM asked Microsoft to release a version of DOS that was compatible with a [[hard disk drive]], [[PC&nbsp;DOS 2.0]] was an almost complete rewrite of DOS, so by March 1983, very little of 86-DOS remained. The most enduring element of 86-DOS was its primitive line editor, [[EDLIN]], which remained the only editor supplied with Microsoft versions of DOS until the June 1991 release of [[MS-DOS 5.0]], which included a [[text-based user interface]] editor called [[MS-DOS Editor]], based on [[QBasic]]. EDLIN can still be used on contemporary machines, since there is an emulated DOS environment up to Windows 10 (32 bit).

===Supported disk formats{{Anchor|Formats}}===
Seattle Computer Products' 86-DOS supported the [[File Allocation Table#FAT12|FAT12]] filesystem on a range of 8-inch and 5.25-inch floppy disk drives on [[S-100 bus|S-100]] floppy disk controller hardware manufactured by [[Cromemco]], [[Tarbell Cassette Interface|Tarbell Electronics]] and [[North Star Computers]]. The [[Western Digital FD1771]]-based Cromemco and Tarbell boards supported one-sided, single-density soft-sectored drives. A Tarbell double-density board utilizing the [[Western Digital FD1771|FD1791]] was supported as well. Later, SCP offered advanced floppy disk controllers, like the Disk Master series.

86-DOS<!-- at least up to including 1.00 --> did not take advantage of a [[Design of the FAT file system#FATID|FAT ID]] byte<ref group="nb" name="NB_FATID_FEh" /> or [[BIOS parameter block]] (BPB), as later DOS versions do, to distinguish between different media formats; instead different drive letters were hard-coded at time of compilation to be associated with different physical floppy drives, sides and densities. That meant, depending on its type, a disk had to be addressed under a certain drive letter to be recognized correctly.  This concept was later emulated with more flexibility by [[DRIVER.SYS]] under DOS 3.x and later versions.

Two logical format variants of the 86-DOS 12-bit FAT format existed—the original format with 16-byte directory entries and the later format (since [[86-DOS#0B|86-DOS 0.42]]) with 32-byte directory entries. Only the second one is logically compatible with the FAT12 format known since the release of MS-DOS and PC&nbsp;DOS. MS-DOS still cannot mount such volumes, as in absence of a BPB it falls back to retrieve the FAT ID in the FAT entry for [[Design of the FAT file system#CLUST 0|cluster 0]] to choose among hard-coded disk geometry profiles. In all formats of a volume formatted under MS-DOS that would otherwise be supported by both systems and typically also in all other formats, this ID is located in the first byte of logical sector 1—that is, the volume's second sector with physical [[cylinder-head-sector]] (CHS) address 0/0/2 or [[logical block addressing]] (LBA) address 1—since MS-DOS assumes a single reserved sector, the boot sector. Under 86-DOS, the [[Design of the FAT file system#Bootsector|reserved sectors area]] is significantly larger (whole tracks), and therefore the prototypical<!-- because 86-DOS does not make use of it, at least not in early versions --> FAT ID {{code|0xFE}} (and {{code|0xFF}}) is located elsewhere on disk, making it impossible for MS-DOS to retrieve it, and even if it would, the hard-coded disk profile associated with it would not take this larger reserved sectors region under 86-DOS into account.<ref group="nb" name="NB_FATID_FEh" />

[[CP/M|CP/M&nbsp;2]] floppy media were readable through [[#RDCPM|RDCPM]].

86-DOS did not offer any specific support for [[Hard disk drive|fixed disks]], but third-party solutions in form of hard disk controllers and corresponding I/O system extensions for 86-DOS were available from companies like [[Tallgrass Technologies]], making hard disks accessible similar to [[Floppy disk variants#Superfloppy|superfloppies]] within the size limits of the FAT12 file system.<!-- most probably without any kind of partitioning, but if so, not in the later MBR partitioning scheme as introduced with PC DOS 2.0 -->

{| class="wikitable" style="text-align:right;"
|-
! style="text-align:right;" | Size
| [[Floppy disk#8.0|8&nbsp;inch]] || <!-- 8&nbsp;inch || -->8&nbsp;inch || 8&nbsp;inch || [[Floppy disk#5.25|5.25&nbsp;inch]] || 5.25&nbsp;inch
|-
! style="text-align:right;" | Density
| [[Disk density#SD|SD]] || <!-- SD || -->[[Disk density#DD|DD]] || DD || SD || SD
|-
! style="text-align:right;" | Modulation
| [[Frequency modulation|FM]] || <!-- FM || -->[[Modified Frequency Modulation|MFM]] || MFM || FM || FM
|-
! style="text-align:right;" | Formatted capacity (KB)
| 250.25<ref name="86-DOS_Files" />
| | <!-- 500.5 || -->616<ref name="86-DOS_Files" />
| | 1232<ref name="86-DOS_Files" />
| | 90<ref name="86-DOS_Files" />
| | 87.5<ref name="86-DOS_Files" />
|-
! style="text-align:right;" | Cylinders (CHS)
| 77 || <!-- 77 || -->77 || 77 || 40 || 35
|-
! style="text-align:right;" | Physical sectors / track
| 26 || <!-- 26 || -->8 || 8 || 18 || 10
|-
! style="text-align:right;" | Number of heads
| 1 || <!-- 2 || -->1 || 2 || 1 || 1
|-
! style="text-align:right;" | Byte payload / physical sector
| 128 || <!-- 128 || -->1024 || 1024 || 128 || 256
|-
! style="text-align:right;" | Bytes / logical sector
| 128 || <!-- 128 || -->1024 || 1024 || 128 || 256
|-
! style="text-align:right;" | Logical sectors / cluster
| 4 || <!-- 4 || -->1 || 1 || 2 || 1
|-
! style="text-align:right;" | Reserved logical sectors
| 52 (2 tracks) || <!-- ? || -->1 || 1 || 54 (3 tracks) || 30 (3 tracks)
|-
! style="text-align:right;" | Number of FATs
| 2 || <!-- 2 || -->2 || 2 || 2 || 2
|-
! style="text-align:right;" | Root directory entries<br />(á 32 bytes,<br />86-DOS 0.42 and higher only)
| 64 (16 sectors) || <!-- 64 (16 sectors) || -->96 (3 sectors) || 128 (4 sectors) || 64 (16 sectors) || 64 (8 sectors)
|-
! style="text-align:right;" | Root directory entries<br />(á 16 bytes)
| 64 || <!-- 64 || -->{{dunno}} || {{dunno}} || 64 || {{N/A}}
|-
! style="text-align:right;" | Total logical sectors
| 2002 || <!-- 4004 || -->616 || 1232 || 720 || 350
|-
! style="text-align:right;" | Logical sectors / FAT
| {{dunno|6?}} || <!-- ? || -->{{dunno}} || {{dunno}} || {{dunno}} || {{dunno}}
|-
! style="text-align:right;" | Hidden sectors
| 0 || <!-- 0 || -->0 || 0 || 0 || 0
|-
! style="text-align:right;" | Logical sector order
| {{dunno}} || <!-- ? || -->{{dunno}} || {{dunno}} || {{dunno}} || {{dunno}}
|-
<!-- | Sector interleave || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} -->
<!-- | Head skew || {{N/A}} || {{dunno}} || {{N/A}} || {{dunno}} || {{N/A}} || {{N/A}} -->
! style="text-align:right;" | Sector mapping
| sector+/ track+ || <!-- sector+/ head+/ track+? --><!-- or sector+/ track+/ head+? --><!-- || -->sector+/ track+ || sector+/ head+/ track+ || sector+/ track+ || sector+/ track+
|-
! style="text-align:right;" | First physical sector
| 1 || <!-- 1 || --> 1 || 1 || 1 || 0
|-
! style="text-align:right;" | Sector index
| [[Floppy disk|Soft]] || <!-- Soft || --> Soft || Soft || Soft || [[Hard sectoring|Hard]] (10+1)
|-
! style="text-align:right;" | Controller type
| Cromemco/Tarbell [[Western Digital FD1771|FD1771]] || <!-- ? --><!-- not sure if the 500.5 KB format is actually supported by 86-DOS. If so, only by Tarbell --><!-- || -->[[Tarbell Cassette Interface|Tarbell]] [[Western Digital FD1771|FD1791]] || Tarbell FD1791 || [[Cromemco]] FD1771 || [[North Star Computers|NorthStar]]<!-- with Shugart SA-400 drives -->
|-
! style="text-align:right;" | [[Design of the FAT file system#FATID|FAT ID]]
| {{No}} (FEh)<ref group="nb" name="NB_FATID_FEh" /> || <!-- No || -->{{No}} (FEh)<ref group="nb" name="NB_FATID_ELSE" /> || {{No}} (FEh)<ref group="nb" name="NB_FATID_ELSE" /> || {{No}} (FEh)<ref group="nb" name="NB_FATID_ELSE" /> || {{No}} (FEh)<ref group="nb" name="NB_FATID_ELSE" />
|-
! style="text-align:right;" | [[BIOS parameter block|BPB]] presence
| {{No}} || <!-- No || -->{{No}} || {{No}} || {{No}} || {{No}}
|}

Various OEM versions of MS-DOS 1.2x and 2.x supported a number of similar 8-inch FAT12 floppy disk formats as well, although not identical to those supported by 86-DOS.<ref group="nb" name="NB_FATID_FEh" />

Disk formats supported by one of the last versions<!-- 1.25 or 1.26 --> developed by Tim Paterson at Microsoft, [[SCP MS-DOS 1.25|MS-DOS 1.25]]<!-- circular link --> <ref name="Paterson_2014_MSDOS125" /><ref name="SCP_MS-DOS_1.25_Files" /><ref name="Shustek_2014_MS-DOS" /><ref name="Levin_2014_MS-DOS" /> (March 1982) for the ''SCP Gazelle'' computer with SCP controller or Cromemco 16FDC controller (by default, this version only supported the MS-DOS-compatible variants of the 8.0&nbsp;in formats with a single reserved sector but it could be built to provide two extra drive letters to read and write floppies in the previous SCP 86-DOS 8.0&nbsp;in disk formats since 0.42 as well):

{| class="wikitable" style="text-align:right;"
|-
! style="text-align:right;" | Size
| [[Floppy disk#8.0|8&nbsp;inch]] || 8&nbsp;inch || <!-- 8&nbsp;inch || -->8&nbsp;inch || 8&nbsp;inch || 8&nbsp;inch || [[Floppy disk#5.25|5.25]]&nbsp;inch || 5.25&nbsp;inch || 5.25&nbsp;inch
|-
! style="text-align:right;" | Density
| [[Disk density#SD|SD]] || SD || <!-- SD || -->[[Disk density#DD|DD]] || DD || DD || SD || DD || DD
|-
! style="text-align:right;" | Modulation
| [[Frequency modulation|FM]] || FM || <!-- FM || -->[[Modified Frequency Modulation|MFM]] || MFM || MFM || FM || MFM || MFM
|-
! style="text-align:right;" | Formatted capacity (KB)
| style="background:#F2F2F2;" | 250.25 (SCP) || 250.25 (MS) || <!-- 500.5 || -->616 || style="background:#F2F2F2;" | 1232 (SCP) || 1232 (MS) || 90 || 160 || 320
|-
! style="text-align:right;" | Cylinders (CHS)
| 77 || 77 || <!-- 77 || -->77 || 77 || 77 || 40 || 40 || 40
|-
! style="text-align:right;" | Physical sectors / track<ref group="nb" name="NB_BPB_0Dh" />
| 26 || 26 || <!-- 26 || -->8 || 8 || 8 || 18 || 8 || 8
|-
! style="text-align:right;" | Number of heads<ref group="nb" name="NB_BPB_0Fh" />
| 1 || 1 || <!-- 2 || -->1 || 2 || 2 || 1 || 1 || 2
|-
! style="text-align:right;" | Byte payload / physical sector
| 128 || 128 || <!-- 128 || -->1024 || 1024 || 1024 || 128 || 512 || 512
|-
! style="text-align:right;" | Bytes / logical sector<ref group="nb" name="NB_BPB_00h" />
| 128 || 128 || <!-- 128 || -->1024 || 1024 || 1024 || 128 || 512 || 512
|-
! style="text-align:right;" | Logical sectors / cluster<ref group="nb" name="NB_BPB_02h" />
| 4 || 4 || <!-- 4 || -->1 || 1 || 1 || 2 || 1 || 2
|-
! style="text-align:right;" | Reserved logical sectors<ref group="nb" name="NB_BPB_03h" />
| style="background:#F2F2F2;" | 52 (2 tracks) || 1 || <!-- ? || -->1 || 1 || 1 || 54 (3 tracks) || 1 || 1
|-
! style="text-align:right;" | Number of FATs<ref group="nb" name="NB_BPB_05h" />
| 2 || 2 || <!-- 2 || -->2 || 2 || 2 || 2 || 2 || 2
|-
! style="text-align:right;" | Root directory entries<br />(á 32 bytes)<ref group="nb" name="NB_BPB_06h" />
| style="background:#F2F2F2;" | 64 (16 sectors) || 68 (17 sectors) || <!-- 64? (16? sectors) || -->96 (3 sectors) || style="background:#F2F2F2;" | 128 (4 sectors) || 192 (6 sectors) || 64 (16 sectors) || 64 (4 sectors) || 112 (7 sectors)
|-
! style="text-align:right;" | Total logical sectors<ref group="nb" name="NB_BPB_08h" />
| 2002 || 2002 || <!-- 4004 || -->616 || 1232 || 1232 || 720 || 320 || 640
|-
! style="text-align:right;" | Logical sectors / FAT<ref group="nb" name="NB_BPB_0Bh" />
| {{dunno|style=background:#F2F2F2;|6?}} || 6 || <!-- ? || -->1 || {{dunno|style=background:#F2F2F2;}} || 2 || 4 || 1 || 1
|-
! style="text-align:right;" | Hidden sectors<ref group="nb" name="NB_BPB_11h" />
| 0 || 0<ref group="nb" name="NB_Microsoft_Hidden" /> || <!-- 0 || -->0 || 0 || 0 || 0 || 0 || 0
|-
! style="text-align:right;" | Total number of clusters<!-- unless there were bad sectors -->
| {{dunno}} || 497 || <!-- ? || -->{{dunno}} || {{dunno}} || 1227 || {{dunno}} || 313 || 315
|-
! style="text-align:right;" | Logical sector order
| {{dunno}} || {{dunno}} || <!-- ? || -->{{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}}
|-
<!-- | Sector interleave || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} || {{dunno}} -->
<!-- | Head skew || {{N/A}} || {{N/A}} || {{dunno}} || {{N/A}} || {{N/A}} || {{dunno}} || {{N/A}} || {{N/A}} || {{dunno}} -->
! style="text-align:right;" | Sector mapping
| sector+/ track+ || sector+/ track+ || <!-- sector+/ head+/ track+? --><!-- or sector+/ track+/ head+? --><!-- || -->sector+/ track+ || sector+/ head+/ track+ || sector+/ head+/ track+ || sector+/ track+ || sector+/ track+ || sector+/ head+/ track+
|-
! style="text-align:right;" | First physical sector
| 1 || 1 || <!-- 1 || --> 1 || 1 || 1 || 1 || 1 || 1
|-
! style="text-align:right;" | Sector index
| [[Floppy disk|Soft]] || Soft || <!-- Soft || --> Soft || Soft || Soft || Soft || Soft || Soft
|-
! style="text-align:right;" | Controller type
| Cromemco&nbsp;/ Tarbell [[Western Digital FD1771|FD1771]] || Cromemco&nbsp;/ Tarbell FD1771 || <!-- ? --><!-- not sure if the 500.5 KB format is actually supported by 86-DOS. If so, only by Tarbell --><!-- || -->[[Tarbell Cassette Interface|Tarbell]] [[Western Digital FD1771|FD1791]]&nbsp;/ [[Western Digital FD1771|FD1793]] || Tarbell FD1791&nbsp;/ FD1793 || Tarbell FD1791&nbsp;/ FD1793 || [[Cromemco]] 4FDC FD1771 || SCP / Cromemco 16FDC || SCP / Cromemco 16FDC
|-
! style="text-align:right;" | [[Design of the FAT file system#FATID|FAT ID]]<ref group="nb" name="NB_FATID_FEh" /><ref group="nb" name="NB_BPB_0Ah" />
| FEh || FEh || <!-- || -->FEh || FEh || FEh || FEh || FEh || FFh
|-
! style="text-align:right;" | [[BIOS parameter block|BPB]] Presence
| {{No}} || {{No}} || <!-- No || -->{{No}} || {{No}} || {{No}} || {{No}} || {{No}} || {{No}}
|}
In 1984 Seattle Computer Products released an OEM version of [[SCP MS-DOS 2.0|MS-DOS 2.0]]<!-- circular link --> for the SCP S-100 computer with SCP-500 Disk Master Floppy controller. It added support for 5.25&nbsp;in DD/1S (180&nbsp;KB) and DD/2S (360&nbsp;KB) FAT12 formats and supported the older formats as well<!-- at least 8.0 in DD/1S on Qume QumeTrak 842 and 5.25 in DD/2S on TEAC FD-55B-01-U. -->, although possibly with some of the parameters<!-- TDB: reserved sectors, FAT ID, BPB --> modified compared to [[MS-DOS 1.25]].<ref name="Bob_2009" />

==See also==
* [[MIDAS (operating system)|MIDAS]]<!-- a Microsoft system implementing FAT -->
* [[MSX-DOS]]<!-- sort of opposite approach: "DOS look&feel but 8-bit CP/M compatible" -->

==Notes==
{{reflist|group="nb"|refs=
<ref group="nb" name="NB_BPB_00h">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the bytes per logical sector corresponds with BPB offset [[Design of the FAT file system#BPB20 OFS 00h|{{code|0x00}}]] under DOS 2.0 and higher.</ref>
<ref group="nb" name="NB_BPB_02h">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the logical sectors per cluster (allocation units) corresponds with BPB offset [[Design of the FAT file system#BPB20 OFS 02h|{{code|0x02}}]] under DOS 2.0 and higher.</ref>
<ref group="nb" name="NB_BPB_03h">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the number of reserved logical sectors corresponds with BPB offset [[Design of the FAT file system#BPB20 OFS 03h|{{code|0x03}}]] under DOS 2.0 and higher.</ref>
<ref group="nb" name="NB_BPB_05h">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the number of FATs corresponds with BPB offset [[Design of the FAT file system#BPB20 OFS 05h|{{code|0x05}}]] under DOS 2.0 and higher.</ref>
<ref group="nb" name="NB_BPB_06h">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the number of root directory entries (á 32 bytes) corresponds with BPB offset [[Design of the FAT file system#BPB20 OFS 06h|{{code|0x06}}]] under DOS 2.0 and higher.</ref>
<ref group="nb" name="NB_BPB_08h">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the total number of logical sectors corresponds with BPB offset [[Design of the FAT file system#BPB20 OFS 08h|{{code|0x08}}]] under DOS 2.0 and higher.</ref>
<ref group="nb" name="NB_BPB_0Ah">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the [[FAT ID]] corresponds with the media descriptor byte at BPB offset [[Design of the FAT file system#BPB20 OFS 0Ah|{{code|0x0A}}]] under DOS 2.0 and higher.</ref>
<ref group="nb" name="NB_BPB_0Bh">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the number of logical sectors per FAT corresponds with BPB offset [[Design of the FAT file system#BPB20 OFS 0Bh|{{code|0x0B}}]] under DOS 2.0 and higher.</ref>
<ref group="nb" name="NB_BPB_0Dh">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the number of physical sectors per track corresponds with BPB offset [[Design of the FAT file system#BPB30 OFS 0Dh|{{code|0x0D}}]] under DOS 3.0 and higher.</ref>
<ref group="nb" name="NB_BPB_0Fh">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the number of heads corresponds with BPB offset [[Design of the FAT file system#BPB30 OFS 0Fh|{{code|0x0F}}]] under DOS 3.0 and higher.</ref>
<ref group="nb" name="NB_BPB_11h">DOS 1.x does not support a [[BIOS Parameter Block|BPB]], but this entry for the number of hidden sectors corresponds with BPB offset [[Design of the FAT file system#BPB30 OFS 11h|{{code|0x11}}]] under DOS 3.0 and higher.</ref>
<ref group="nb" name="NB_FATID_FEh">8.0" 250.25&nbsp;KB images formatted under 86-DOS 1.00 sport a FAT ID of FEh, however, in contrast to MS-DOS/PC&nbsp;DOS, 86-DOS does not seem to use this to detect the disk format, as this information is hard-coded into disk profiles associated to certain drive letters at compile-time. MS-DOS would not be able to mount such volumes as (in absence of a BPB) it expects the FAT ID in logical sector 1, assuming only one reserved sector of 512 bytes (the boot sector in logical sector 0) instead of the 52 reserved sectors á 128 bytes used by 86-DOS here. This works for MS-DOS, because the system files are not part of the reserved area under MS-DOS, while under 86-DOS there are no system files and the ca. 6&nbsp;KB large DOS kernel is located in the reserved area.</ref>
<ref group="nb" name="NB_FATID_ELSE">Executing the [[CLEAR (DOS command)|{{code|CLEAR}}]] command under 86-DOS 1.00 COMMAND.COM seems to initialize a volume's FAT&nbsp;ID byte to FEh regardless of disk drive and format used.<!-- Still needs verification on live media, though. Seen live on 250&nbsp;KB media only, so far. --></ref>
<ref group="nb" name="NB_Microsoft_Hidden">For unknown reasons, some Microsoft documents give a value of 3 for this entry, where 0 seems correct technically. SCP MS-DOS 1.25 implicitly assumes 0 as well.</ref>
<ref group="nb" name="NB_Paterson_EasterEgg">Somewhat ironically in the context of [[Jerry Pournelle]]'s claim that [[Gary Kildall]] demonstrated to him a way to display Kildall's name in DOS, [[Tim Paterson]] claims to have hidden an [[easter egg (software)|easter egg]], displaying his ''own'' name, in the [[File Allocation Table|FAT]] code of [[MSX-DOS]] 1, when he developed this [[Z80]]-based [[CP/M]] clone resembling 86-DOS/[[MS-DOS 1.25]] in 1983: {{cite web|first=Tim|last=Paterson|author-link=Tim Paterson|title=The History of MSX-DOS|url=http://www.msx.org/wiki/The_History_of_MSX-DOS|date=2014-02-17|access-date=2014-05-31|publisher=Jorito, Maggoo, John Hassink, MSX Resource Center}}</ref>
}}

==References==
{{reflist|refs=
<ref name="Freiberger_1984_Fire_Valley">{{cite book |title=Fire in the Valley: The Making of the Personal Computer |author-last1=Freiberger |author-first1=Paul |author-link1=Paul Freiberger |author-first2=Michael |author-last2=Swaine |author-link2=Michael Swaine (technical author) |orig-year=1984 |edition=2nd |date=2000 |publisher=[[McGraw-Hill]] |location=New York |isbn=0-07-135892-7 |pages=[https://archive.org/details/fireinvalleymaki00frei_0/page/332 332–333] |url=https://archive.org/details/fireinvalleymaki00frei_0/page/332 }}</ref>
<ref name="Beley_1986_MS-DOS_Encyclopedia">{{Cite book |editor1-first=Jim |editor1-last=Beley |editor2-first=Barry |editor2-last=Preppernau |editor3-first=Pam |editor3-last=Beason |editor4-first=Andrea |editor4-last=Lewis |editor5-first=David |editor5-last=Rygmyr |author-first1=Howard |author-last1=Bornstein |author-first2=Lawrence |author-last2=Bredehoeft |author-first3=Ray |author-last3=Duncan |author-first4=Carol |author-last4=Morris |author-first5=David |author-last5=Rose <!-- |author-link5=David Rose --> |author-first6=John |author-last6=Socha |author-link6=John Socha |author-first7=Jim |author-last7=Tomlin |author-first8=Kathleen |author-last8=Vian |author-first9=Van |author-last9=Wolverton |title=MS-DOS (Versions 1.0-3.2) Technical Reference Encyclopedia |contribution=Technical advisors |contributor-first1=Paul |contributor-last1=Allen |contributor-link1=Paul Allen |contributor-first2=Bill |contributor-last2=Gates |contributor-link2=Bill Gates |contributor-first3=Adrian |contributor-last3=King |contributor-first4=Chris |contributor-last4=Larson |contributor-first5=Gordon |contributor-last5=Letwin |contributor-link5=Gordon Letwin |contributor-first6=Bob |contributor-last6=O'Rear |contributor-link6=Bob O'Rear |contributor-first7=Tim |contributor-last7=Paterson |contributor-link7=Tim Paterson |contributor-first8=Chris |contributor-last8=Peters |contributor-first9=Bruce |contributor-last9=Phillips |contributor-first10=Aaron |contributor-last10=Reynolds |contributor-link10=Aaron R. Reynolds |contributor-first11=Betty |contributor-last11=Stillmaker |contributor-first12=Mark |contributor-last12=Zbikowski |contributor-link12=Mark Zbikowski |date=1986 |edition=Original withdrawn |publisher=[[Microsoft Press]] |series=Microsoft Reference Library |volume=1 |location=Redmond, Washington, USA |isbn=0-914845-69-1 |lccn=86-8640 |oclc=635600205}} (xvii+1053 pages; 29&nbsp;cm) (NB. This original edition contains flowcharts of the internal workings of the system. It was withdrawn by Microsoft before mass-distribution in 1986 because it contained many factual errors as well as some classified information which should not have been published. Few printed copies survived. It was replaced by a completely reworked edition in 1988. [https://blogs.msdn.microsoft.com/larryosterman/2004/06/14/does-anyone-remember-the-original-ms-dos-encyclopedia/])</ref>
<ref name="Duncan_1988_MS-DOS_Encyclopedia">{{Cite book |title=The MS-DOS Encyclopedia: versions 1.0 through 3.2 |author-first1=Ray |author-last1=Duncan |author-first2=Steve |author-last2=Bostwick |author-first3=Keith |author-last3=Burgoyne |author-first4=Robert A. |author-last4=Byers |author-first5=Thom |author-last5=Hogan |author-first6=Jim |author-last6=Kyle |author-first7=Gordon |author-last7=Letwin |author-link7=Gordon Letwin |author-first8=Charles |author-last8=Petzold |author-link8=Charles Petzold |author-first9=Chip |author-last9=Rabinowitz |author-first10=Jim |author-last10=Tomlin |author-first11=Richard |author-last11=Wilton |author-first12=Van |author-last12=Wolverton |author-first13=William |author-last13=Wong |author-first14=JoAnne |author-last14=Woodcock |contribution=Technical advisors |contributor-first1=Mark |contributor-last1=Zbikowski |contributor-link1=Mark Zbikowski |contributor-first2=Paul |contributor-last2=Allen |contributor-link2=Paul Allen |contributor-first3=Steve |contributor-last3=Ballmer |contributor-link3=Steve Ballmer |contributor-first4=Reuben |contributor-last4=Borman |contributor-first5=Rob |contributor-last5=Borman |contributor-first6=John |contributor-last6=Butler |contributor-first7=Chuck |contributor-last7=Carroll |contributor-first8=Mark |contributor-last8=Chamberlain |contributor-first9=David |contributor-last9=Chell |contributor-first10=Mike |contributor-last10=Colee |contributor-first11=Mike |contributor-last11=Courtney |contributor-first12=Mike |contributor-last12=Dryfoos |contributor-first13=Rachel |contributor-last13=Duncan |contributor-first14=Kurt |contributor-last14=Eckhardt |contributor-first15=Eric |contributor-last15=Evans |contributor-first16=Rick |contributor-last16=Farmer |contributor-first17=Bill |contributor-last17=Gates |contributor-link17=Bill Gates |contributor-first18=Michael |contributor-last18=Geary |contributor-first19=Bob |contributor-last19=Griffin |contributor-first20=Doug |contributor-last20=Hogarth |contributor-first21=James W. |contributor-last21=Johnson |contributor-first22=Kaamel |contributor-last22=Kermaani |contributor-first23=Adrian |contributor-last23=King |contributor-first24=Reed |contributor-last24=Koch |contributor-first25=James |contributor-last25=Landowski |contributor-first26=Chris |contributor-last26=Larson |contributor-first27=Thomas |contributor-last27=Lennon |contributor-first28=Dan |contributor-last28=Lipkie |contributor-first29=Marc |contributor-last29=McDonald |contributor-link29=Marc McDonald |contributor-first30=Bruce |contributor-last30=McKinney |contributor-first31=Pascal |contributor-last31=Martin |contributor-first32=Estelle |contributor-last32=Mathers |contributor-first33=Bob |contributor-last33=Matthews <!-- |contributor-link33=Robert Matthews (scientist)??? --> |contributor-first34=David |contributor-last34=Melin |contributor-first35=Charles |contributor-last35=Mergentime |contributor-first36=Randy |contributor-last36=Nevin |contributor-first37=Dan |contributor-last37=Newell |contributor-first38=Tani |contributor-last38=Newell |contributor-first39=David |contributor-last39=Norris |contributor-first40=Mike |contributor-last40=O'Leary |contributor-first41=Bob |contributor-last41=O'Rear |contributor-link41=Bob O'Rear |contributor-first42=Mike |contributor-last42=Olsson |contributor-first43=Larry |contributor-last43=Osterman |contributor-first44=Ridge |contributor-last44=Ostling |contributor-first45=Sunil |contributor-last45=Pai |contributor-first46=Tim |contributor-last46=Paterson |contributor-link46=Tim Paterson |contributor-first47=Gary |contributor-last47=Perez |contributor-first48=Chris |contributor-last48=Peters |contributor-first49=Charles |contributor-last49=Petzold |contributor-link49=Charles Petzold |contributor-first50=John |contributor-last50=Pollock |contributor-first51=Aaron |contributor-last51=Reynolds |contributor-link51=Aaron R. Reynolds |contributor-first52=Darryl |contributor-last52=Rubin |contributor-first53=Ralph |contributor-last53=Ryan |contributor-first54=Karl |contributor-last54=Schulmeisters |contributor-first55=Rajen |contributor-last55=Shah |contributor-first56=Barry |contributor-last56=Shaw |contributor-first57=Anthony |contributor-last57=Short |contributor-first58=Ben |contributor-last58=Slivka |contributor-first59=Jon |contributor-last59=Smirl |contributor-first60=Betty |contributor-last60=Stillmaker |contributor-first61=John |contributor-last61=Stoddard |contributor-first62=Dennis |contributor-last62=Tillman |contributor-first63=Greg |contributor-last63=Whitten |contributor-first64=Natalie |contributor-last64=Yount |contributor-first65=Steve |contributor-last65=Zeck |date=1988 |edition=Completely reworked |publisher=[[Microsoft Press]] |location=Redmond, Washington, USA |isbn=1-55615-049-0 |lccn=87-21452 |oclc=16581341 |page=20}} (xix+1570 pages; 26&nbsp;cm) (NB. This edition was published in 1988 after extensive rework of the withdrawn 1986 first edition by a different team of authors. [https://www.pcjs.org/pubs/pc/reference/microsoft/mspl13/msdos/encyclopedia/])</ref>
<ref name="TWIT_2006">{{cite podcast |url=http://www.twit.tv/73 |title=this WEEK in TECH |website=The TWiT Netcast Network |date=2006-10-16 |access-date=2006-11-28 |archive-url=https://archive.today/20130418203921/http://www.twit.tv/73 |archive-date=2013-04-18 |url-status=dead}}</ref>
<ref name="Evans_2004_They_Made_America">{{cite book |author-first1=Harold |author-last1=Evans |author-link1=Harold Evans |author-first2=Gail |author-last2=Buckland |author-first3=David |author-last3=Lefer |author-link3=David Lefer |date=2004 |title=They Made America: From the Steam Engine to the Search Engine: Two Centuries of Innovators |publisher=[[Little, Brown and Co.]] |isbn=0-316-27766-5 |url=https://archive.org/details/theymadeamericaf00evan}}</ref>
<ref name="Paterson_1994_Origins_DOS">{{cite journal |title=The Origins of DOS: DOS Creator Gives His View of Relationship Between CP/M, MS-DOS |author-last=Paterson |author-first=Tim |author-link=Tim Paterson |journal=[[Microprocessor Report]] |publisher=[[MicroDesign Resources]] (MDR) |volume=8 |issue=13 |date=1994-10-03 |issn=0899-9341 |url=http://www.ece.umd.edu/courses/enee759m.S2000/papers/paterson1994-kildall.pdf |archive-url=https://web.archive.org/web/20120531090452/http://www.ece.umd.edu/courses/enee759m.S2000/papers/paterson1994-kildall.pdf |archive-date=2012-05-31}}</ref>
<ref name="USA_Today_2005_Programmer_Sues">{{cite news |title=Programmer sues author over role in Microsoft history |agency=Associated Press |date=2005-02-03 |work=[[USA Today]] |url=https://www.usatoday.com/tech/news/2005-03-02-ms-coding-dis_x.htm |access-date=2006-11-28}}</ref>
<ref name="Paterson_2007_Design-DOS">{{cite web |title=Design of DOS |author-first=Tim |author-last=Paterson |author-link=Tim Paterson |work=DosMan Drivel |date=2007-09-30 |url=http://dosmandrivel.blogspot.com/2007/09/design-of-dos.html |access-date=2011-07-04 |archive-url=https://web.archive.org/web/20130120075653/http://dosmandrivel.blogspot.com/2007/09/design-of-dos.html |archive-date=2013-01-20}}</ref>
<ref name="Hunter_1983_Roots_of_DOS">{{cite magazine |title=The Roots of DOS: Tim Paterson |author-first=David |author-last=Hunter |magazine=[[Softalk]] |date=March 1983 |url=http://www.patersontech.com/dos/softalk.aspx |access-date=2013-08-18 |archive-url=https://web.archive.org/web/20190906120449/http://www.patersontech.com/dos/softalk.aspx |archive-date=6 September 2019 |url-status=dead }}</ref>
<ref name="SCP_1981_86-DOS_1.0_Addendum">{{cite web |title=SCP 86-DOS 1.0 Addendum |author=Seattle Computer Products |author-link=Seattle Computer Products |date=1981 |url=http://bitsavers.informatik.uni-stuttgart.de/pdf/seattleComputer/86-DOS_1.0_Addendum.pdf |access-date=2013-04-02 |url-status=live |archive-url=https://web.archive.org/web/20200219013028/http://bitsavers.informatik.uni-stuttgart.de/pdf/seattleComputer/86-DOS_1.0_Addendum.pdf |archive-date=2020-02-19}} (1+14+1 pages)</ref>
<ref name="Paterson_1983_Byte_Short_History">{{cite journal |title=A Short History of MS-DOS |author-last=Paterson |author-first=Tim |author-link=Tim Paterson |date=June 1983 |journal=[[Byte (magazine)|Byte]] |issn=0360-5280 |volume=8 |edition=6 |url=http://www.patersontech.com/dos/byte%E2%80%93history.aspx |access-date=2013-08-18 |archive-url=https://web.archive.org/web/20151031040606/http://www.patersontech.com/dos/byte%E2%80%93history.aspx |archive-date=31 October 2015 |url-status=dead }} (NB. This source mentions the 1981-07-27 as the date of purchase.)</ref>
<ref name="nerds2">{{cite episode |title=Part II |url=https://www.pbs.org/nerds/part2.html |series=Triumph of the Nerds: The Rise of Accidental Empires |credits=Cringely, Robert X. |network=PBS |airdate=June 1996 |season=1}}</ref>
<ref name="BYTE_1980_86-DOS">{{cite magazine |title=86-DOS - 8086 OPERATING SYSTEM - $95 |author=Seattle Computer Products |author-link=Seattle Computer Products |magazine=[[Byte (magazine)|Byte]] |volume=5 |number=8 |date=August 1980 |publisher=[[BYTE Publications Inc.]] |issn=0360-5280 |id={{CODEN|BYTEDJ}} |type=Advertisement |page=173 |url=https://archive.org/stream/byte-magazine-1980-08/1980_08_BYTE_05-08_The_Forth_Language#page/n173/mode/2up
|access-date=2013-08-18 }} [https://tech-insider.org/personal-computers/research/acrobat/8008-a.pdf] (NB. The SCP advertisement already calls the product ''86-DOS'', but does not mention a specific version number. Version 0.3 is known to be called 86-DOS already, so the name change must have taken place either for version 0.2 or immediately afterwards in August 1980.)</ref>
<ref name="Schulman_1994_Undocumented-DOS">{{cite book |author-first1=Andrew |author-last1=Schulman |author-first2=Ralf D. |author-last2=Brown |author-link2=Ralf D. Brown |author-first3=David |author-last3=Maxey |author-first4=Raymond J. |author-last4=Michels |author-first5=Jim |author-last5=Kyle |title=Undocumented DOS: A programmer's guide to reserved MS-DOS functions and data structures - expanded to include MS-DOS 6, Novell DOS and Windows 3.1 |publisher=[[Addison Wesley]] |edition=2 |date=1994 |orig-year=November 1993<!-- first printing --> |isbn=0-201-63287-X |location=Reading, Massachusetts |url=https://archive.org/details/undocumenteddosp00andr_0 }} (xviii+856+vi pages, 3.5"-floppy) Errata: [https://web.archive.org/web/20190417215556/http://www.cs.cmu.edu/afs/cs/user/ralf/pub/books/UndocumentedDOS/errata.ud2][https://web.archive.org/web/20190417212906/https://www.pcjs.org/pubs/pc/programming/Undocumented_DOS/#errata-2nd-edition]</ref>
<ref name="paterson198306">{{cite journal |author-last=Paterson |author-first=Tim |author-link=Tim Paterson |title=An Inside Look at MS-DOS - The design decisions behind the popular operating system |journal=[[Byte (magazine)|Byte]] |publisher=[[Byte Publications Inc.]] |volume=8 |series=6 |date=June 1983 |url=https://archive.org/stream/byte-magazine-1983-06/1983_06_BYTE_08-06_16-Bit_Designs#page/n229/mode/2up |access-date=2013-10-19 |pages=230}} (NB. The article often uses "MS-DOS" to refer to both 86-DOS and MS-DOS, but mentions QDOS and 86-DOS in a sidebar article, "A Short History of MS-DOS".)</ref>
<ref name="edlin19820607">{{cite journal |author-first=Jim |author-last=Edlin |title=CP/M Arrives - IBM releases a tailed-for-the-PC version of CP/M-86 that profits from the learning curve |journal=[[PC Magazine]] |date=1982-06-07 |url=https://books.google.com/books?id=w_OhaFDePS4C&pg=RA2-PA43 |access-date=2013-10-21 |pages=43}}</ref>
<ref name="Paterson_2014_MSDOS125">{{cite web |author-first=Tim |author-last=Paterson |author-link=Tim Paterson |title=Microsoft DOS V1.1 and V2.0: /msdos/v11source/MSDOS.ASM |url=http://www.computerhistory.org/atchm/microsoft-research-license-agreement-msdos-v1-1-v2-0/ |publisher=[[Computer History Museum]], [[Microsoft]] |date=2013-12-19<!-- 2014-03-25 --> |orig-year=1983<!-- 1983-05-17 --> |access-date=2014-03-25}} (NB. While the publishers claim this would be MS-DOS 1.1 and 2.0, it actually is [[SCP MS-DOS 1.25]] and a mixture of [[Altos MS-DOS 2.11]] and [[TeleVideo PC DOS 2.11]].)</ref>
<ref name="Shustek_2014_MS-DOS">{{cite web |url=http://www.computerhistory.org/atchm/microsoft-ms-dos-early-source-code/ |title=Microsoft MS-DOS early source code |series=Software Gems: [[The Computer History Museum]] Historical Source Code Series |author-first=Len |author-last=Shustek |date=2014-03-24 |access-date=2014-03-29}} (NB. While the author claims this would be MS-DOS 1.1 and 2.0, it actually is [[SCP MS-DOS 1.25]] and a mixture of [[Altos MS-DOS 2.11]] and [[TeleVideo PC DOS 2.11]].)</ref>
<ref name="Levin_2014_MS-DOS">{{cite web |url=http://blogs.technet.com/b/microsoft_blog/archive/2014/03/25/microsoft-makes-source-code-for-ms-dos-and-word-for-windows-available-to-public.aspx |title=Microsoft makes source code for MS-DOS and Word for Windows available to public |date=2014-03-25 |author-first=Roy |author-last=Levin |work=Official Microsoft Blog |access-date=2014-03-29 |archive-url=https://web.archive.org/web/20140328094124/http://blogs.technet.com/b/microsoft_blog/archive/2014/03/25/microsoft-makes-source-code-for-ms-dos-and-word-for-windows-available-to-public.aspx |archive-date=2014-03-28 |url-status=dead}} (NB. While the author claims this would be MS-DOS 1.1 and 2.0, it actually is [[SCP MS-DOS 1.25]] and a mixture of [[Altos MS-DOS 2.11]] and [[TeleVideo PC DOS 2.11]].)</ref>
<ref name="Bob_2009">{{cite web |url=http://bartosh.us/s-100/ |archive-url=https://web.archive.org/web/20130904203728/http://bartosh.us/s-100/ |title=Seattle Computer Products 8086 S-100 Bus Microcomputer - Picture of 8.0" DD/1S distribution floppy disks for SCP MS-DOS 2.0 |date=2009-11-22 |archive-date=2013-09-04 |access-date=2014-05-06}}</ref>
<ref name="86-DOS_License">{{cite web |title=86-DOS version 0.3 (1980-11-15) License Agreement between Seattle Computer Products and Microsoft |date=1981-01-06<!-- signed date --> |url=http://antitrust.slated.org/www.iowaconsumercase.org/011607/0000/PX00001.pdf |access-date=2013-04-01 |url-status=live |archive-url=https://web.archive.org/web/20200218165128/http://antitrust.slated.org/www.iowaconsumercase.org/011607/0000/PX00001.pdf |archive-date=2020-02-18}} (NB. Published as part of the [[Comes v. Microsoft]] case as exhibit #1.)</ref>
<ref name="86-DOS_Sale">{{cite web |title=86-DOS Sales Agreement between Seattle Computer Products and Microsoft |date=1981-07-27 |url=http://antitrust.slated.org/www.iowaconsumercase.org/011607/0000/PX00002.pdf |access-date=2013-04-01 |url-status=live |archive-url=https://web.archive.org/web/20200219011420/http://antitrust.slated.org/www.iowaconsumercase.org/011607/0000/PX00002.pdf |archive-date=2020-02-19}} (NB. Published as part of the [[Comes v. Microsoft]] case as exhibit #2. The document also carries a typed date stamp as of 1981-07-22.)</ref>
<ref name="Paterson_v_Little_2007">{{cite web |title=Paterson v. Little, Brown, and Co., et al. - Order |author=United States District Court for the Western District of Washington |author-link=United States District Court for the Western District of Washington |location=Seattle, Washington, USA |newspaper=[[Seattle Times]] |id=Case 2:05-cv-01719-TSZ Document 29 |date=2007-07-25 |orig-year=2005-02-28 |url=http://seattletimes.nwsource.com/ABPub/2007/07/26/2003806592.pdf |access-date=2014-12-21 |url-status=dead |archive-url=https://web.archive.org/web/20181003165746/http://seattletimes.nwsource.com/ABPub/2007/07/26/2003806592.pdf |archive-date=2018-10-03}}</ref>
<ref name="86-DOS_Files">[https://web.archive.org/web/20110724210024/http://www.86dos.org/downloads/86DOS_FILES.ZIP A ZIP file containing most of the files from 86-DOS 0.75 (1981-04-17<!-- change to internal version 0.75 -->/1981-04-18<!-- date stamp of files in archive -->) to 1.00<!-- version in file header -->/1.10<!-- actual internal version as of 1981-07-21 --> (1981-07-21<!-- date stamp of files in archive -->)]</ref>
<ref name="SCP_86-DOS_1.0_Files">[http://www.schorn.ch/cpm/zip/86dos.zip 86-DOS 1.00 disk images for SIMH simulator]</ref><ref name="SCP_MS-DOS_1.25_Files">[http://www.schorn.ch/cpm/zip/msdos125.zip MS-DOS 1.25 disk images for SIMH simulator]</ref>
<ref name="SCP_1980_86-DOS-UM">{{cite book |title=86-DOS - Disk Operating System for the 8086 - User's Manual |edition=Preliminary |version=Version 0.3 |date=1980 |publisher=[[Seattle Computer Products, Inc.]] |location=Seattle, Washington, USA |url=http://www.patersontech.com/Dos/docs/86_Dos_usr_03.pdf |access-date=2019-07-14 |url-status=dead |archive-url=https://web.archive.org/web/20190714004434/http://www.patersontech.com/dos/docs/86_Dos_usr_03.pdf |archive-date=2019-07-14}} (59 pages)</ref>
<ref name="Paterson_1997">{{cite magazine |title=DOS Testimony |author-first=Tim |author-last=Paterson |author-link=Tim Paterson |department=Letters |date=1997-05-06 |magazine=[[PC Magazine]] |issn= |volume=16 |number=9 |publisher=[[Ziff-Davis Publishing Company]] |page=24 |url=https://books.google.com/books?id=FxChL0Kr_3EC&pg=PA24 |access-date=2021-12-03 |url-status=live |archive-url=https://web.archive.org/web/20211203162831/https://books.google.de/books?id=FxChL0Kr_3EC&pg=PA24&lpg=PA24&dq=fat+binary+CP%2FM+DOS&source=bl&ots=SeFn_exfIs&sig=ACfU3U2_QqyBIMQ2fyPm03_R53gpW7tKUw&hl=de&sa=X&ved=2ahUKEwiNhpn4hcj0AhWn_7sIHW1AAho4PBDoAXoECCEQAw#v=onepage&q=fat%20binary%20CP%2FM%20DOS&f=false |archive-date=2021-12-03}}</ref>
}}

==Further reading==
* {{cite book |title=86-DOS - Disk Operating System for the 8086 - Programmer's Manual |edition=Preliminary |version=Version 0.3 |date=1980 |publisher=[[Seattle Computer Products, Inc.]] |location=Seattle, Washington, USA |url=https://bitsavers.org/pdf/seattleComputer/86-DOS_0.3_Programmers_Manual_1980.pdf |access-date=2024-10-13}} (41 pages)

==External links==
* [https://web.archive.org/web/20160506004555/http://www.patersontech.com/dos/origins-of-dos.aspx 86-DOS documentation] from Paterson Technology
* [https://web.archive.org/web/20090208014302/http://www.86dos.org/index.htm Run SCP 86-DOS 1.0] in the Altair 8800 SIMH simulator by Howard M. Harte

{{Disk operating systems}}

{{DEFAULTSORT:86-Dos}}
[[Category:Microcomputer software]]
[[Category:Disk operating systems]]
[[Category:DOS variants]]
[[Category:Floppy disk-based operating systems]]
[[Category:Discontinued operating systems]]
[[Category:Proprietary operating systems]]
[[Category:1979 software]]
[[Category:Assembly language software]]
[[Category:Products and services discontinued in 1981]]