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IBM PC DOS
IBM PC DOS (The IBM Personal Computer DOS, also known as IBM DOS) was an operating system for x86-based IBM personal computers manufactured and sold by IBM. The very first version of PC DOS was released in 1981-08 with the IBM 5150 PC. Up to 1993, PC DOS was developed jointly by Microsoft and IBM. However, after the split between IBM and Microsoft, they each maintained their own variant of DOS separately. IBM PC DOS 7.0 revision 1 (marketed as PC DOS 2000) was the last full version of DOS released by IBM, although some specialized tools make use of various builds of release 7.1 compiled between 2000 and 2003.
IBM PC-DOS 1.0 was a port of 86-DOS purchased by Microsoft in 1981 for use on the IBM PC. This version of DOS resembles that of CP/M at the time. Only 160kB 5.25 inch (134mm) floppies were supported. Directory support did not exist with this version of DOS.
PC-DOS 2.0 was IBM's retail version of MS-DOS branded specifically towards IBM Machines. Version 2.0 of PC-DOS introduced various features inspired of Xenix, a varient of Unix sold by Microsoft. These features included file handles.
PC-DOS 3.x was introduced for IBM's 286 based AT computer. It adds support for IBM's 1.2mb floppy drive, hard disk partitions up to 32mb, and adds features for use with networking.
IBM DOS 4.00 was IBM's first in-house development effort with DOS. Prior to this release, all DOS code had been managed by Microsoft on IBM's behalf (hence the parallel releases). With this version, IBM re-engineered the source and added their own enhancements. PC-DOS 4.00 adds support for drives up 2 gigabytes and a graphical DOS shell. The initial release of IBM PC-DOS 4.00 was extremely buggy. It was quickly followed up by a 4.01 update.
Over all, PC-DOS 5 was much improved over DOS 4. It reduced base 640k memory usage by making use of HMA on 286+ CPUs.
IBM skipped version 6.0 to avoid confusion with MS-DOS 6.0.
PC-DOS 6.1 is quite different from MS-DOS. Instead of Symantec tools, PC-DOS bundles additional disk utilities from Central Point Software. It also bundles IBMs own Antivirus software, and SuperStore disk compression.
PC-DOS 7, AKA "IBM PC DOS 7.00, revision 0", adds the REXX Programming language, XDF 1.86MB 3.5" floppy disk support, and Stacker Disk compression.
PC-DOS 2000 is a minor update to PC-DOS 7.0 that fixes Y2K bugs. It is marketed as "PC-DOS 2000" but it reports itself as "IBM PC DOS 7.00, revision 1".
7.0/2000 was the last complete release. Although some embedded products were released with portions of "PC-DOS 7.1" that added Fat32 support.