Editing IBM PC DOS (section)

=== {{anchor|1.00|1.10}}PC DOS 1.x ===
<!-- What about PC DOS 1.05 and 1.85? Did they really exist? -->
[[File:IBM DOS 1.1 Manual and Disk.jpg|thumb|upright | User manual and diskette for IBM PC&nbsp;DOS 1.1]]
Microsoft first licensed,<ref name="86-DOS_License"/> then purchased<ref name="86-DOS_Sale"/> [[86-DOS]] from [[Seattle Computer Products]] (SCP), which was modified for the IBM PC by Microsoft employee [[Bob O'Rear]] with assistance from SCP (later Microsoft) employee [[Tim Paterson]].<ref name="Paterson_2007"/> O'Rear got 86-DOS to run on the prototype PC in February 1981. 86-DOS had to be converted from 8-inch to 5.25-inch [[floppy disks]] and integrated with the [[BIOS]], which Microsoft was helping IBM to write.<ref name="Beley_1986"/><ref name="Duncan_1988"/> IBM had more people writing requirements for the computer than Microsoft had writing code. O'Rear often felt overwhelmed by the number of people he had to deal with at the ESD (Entry Systems Division) facility in [[Boca Raton, Florida]].

Perhaps the first public mention of the operating system was in July 1981, when ''[[Byte (magazine)|Byte]]'' discussed rumors of a forthcoming personal computer with "a CP/M-like DOS ... to be called, simply, 'IBM Personal Computer DOS{{'"}}.<ref name="Morgan_1981"/> 86-DOS was [[rebranded]] IBM PC&nbsp;DOS 1.0 for its August 1981 release with the IBM PC. The initial version of DOS was largely based on [[CP/M-80]] 1.x and most of its architecture, function calls and file-naming conventions were copied directly from the older OS. The most significant difference was the fact that it introduced a different file system, [[FAT12]]. Unlike all later DOS versions, the {{mono|[[DATE (DOS command)|DATE]]}} and {{mono|[[TIME (DOS command)|TIME]]}} commands were separate executables rather than part of {{mono|[[COMMAND.COM]]}}. Single-sided 160 [[kilobyte]] (KB) 5.25-inch floppies were the only disk format supported.

In late 1981, Paterson, now at Microsoft, began writing PC&nbsp;DOS 1.10. It debuted in May 1982 along with the Revision&nbsp;B IBM PC. Support for the new double-sided drives was added, allowing 320&nbsp;KB per disk. A number of bugs were fixed, and error messages and prompts were made less cryptic. The {{mono|[[DEBUG (DOS command)|DEBUG.EXE]]}} was now able to load files greater than 64&nbsp;KB in size.