© Amit Singh. All Rights Reserved. Written in Mid 2003



The need for DOS keeps arising one way or the other. Consider the following (most of them are contrived, I know):

:: IBM DOS 1.x


The complete history of DOS is too well known to be repeated here. In July 1981, Microsoft bought all rights to DOS from Seattle Computer products, and the name MS-DOS was coined. In August, IBM announced the IBM 5150 Personal Computer (4.77 MHz Intel 8088 Processor, 40 KB ROM, 64 KB RAM, a single 5.25" floppy diskette and PC-DOS 1.0 (no hard disk support). In May, 1982, Microsoft released MS-DOS 1.1 to IBM. It was shipped on the IBM PC as IBM PC-DOS 1.1. It supported 320 KB double-sided floppy disk drives, but no hard disks.

The size of COMMAND.COM was 4959 bytes.

:: MS-DOS 3.x

MS-DOS 3.x

MS-DOS 3.0 was released in August, 1984. It had support for 1.2 MB floppy disk drives, and "large" (larger than 10 MB) hard disks. This version was designed to support newer IBM-AT hardware, and had some very preliminary LAN features.

In November, 1984, Microsoft released MS-DOS 3.1, which had more LAN features.

In January, 1986, Microsoft released MS-DOS 3.2, with support for 3.5" 720 KB floppy drives.

In August, 1987, Microsoft released MS-DOS 3.3, with support for the IBM PS/2 and 3.5" 1.44 MB floppy drives as well as multiple hard disk partitions. This version was also internationalized (support for code-pages for 17 countries).

The size of COMMAND.COM was 25276 bytes on MS-DOS 3.30.

MS-DOS 3.x boots and runs fine under Virtual PC.

:: MS-DOS 4.x

MS-DOS 4.x

Microsoft released MS-DOS 4.0 in June, 1988. 4.0 had several improvements, such as XMS support, larger hard disk partition support (up to 2 GB) and a mouse-driven graphical interface called the DOS SHELL. MS-DOS 4.0 had an abnormally large number of bugs, many of which were fixed in version 4.01 that was released a few months later.

The size of COMMAND.COM was 37557 bytes on MS-DOS 4.01.

MS-DOS 4.x boots and runs fine under Virtual PC.

:: MS-DOS 5.x

MS-DOS 5.x

Microsoft released MS-DOS 5.0 in June, 1991. It had better memory management features (parts of DOS could be loaded in the high memory area, and certain device drivers/TSRs could run in unused parts of the upper memory between 640K and 1M). and several shell enhancements (task swapping, a full-screen editor) and utilities like "UNDELETE" and "UNFORMAT". It also included the DOS Shell that was introduced in MS-DOS 4.0.

Instead of GWBASIC.EXE, this version shipped with QBASIC.EXE, which was based on Microsoft QuickBasic.

The size of COMMAND.COM was 47845 bytes on MS-DOS 5.0.

MS-DOS 5.0 boots and runs fine under Virtual PC.

:: MS-DOS 6.x

MS-DOS 6.x

Microsoft released MS-DOS 6.0 in March, 1993. It included DoubleSpace (disk compression), disk defragmentation, backup utility, anti-virus utility etc. Available as an upgrade, this version sold over a million copies in less than two months.

MS-DOS 6.2 was released in November, 1993, with minor improvements. Version 6.21 followed in Februrary, 1994, with DoubleSpace compression removed. Finally, Microsoft released version 6.22 in June, 1994, with disk compression reintroduced as "DriveSpace".

The sizes of COMMAND.COM were 52925, 54619, 54619 and 54645 bytes on MS-DOS versions 6.0, 6.20, 6.21 and 6.22 respectively.

MS-DOS 6.x boots and runs fine under Virtual PC. Moreover, DOS is an officially supported system on Virtual PC.



DR DOS is an embedded DOS system, designed for implementation into ROM or flash memory. DR DOS is currently owned by DeviceLogics.

DR DOS features include a multitasking API, disk compression and caching, EMM386 support, DPMS support, localizations and networking support. It is also available from DeviceLogics in bundled products for various scenarios such as desktop use, accounting, legal, medical, kiosk etc.

DR DOS boots and runs fine under Virtual PC.

:: FreeDOS


FreeDOS aims to be a complete, free, 100% MS-DOS compatible operating system. Specifically, the kernel is compatible with MS-DOS 3.3, while the programs are compatible with MS-DOS 6.22. It is available both as a bootable diskette image and a bootable CD-ROM image. I find FreeDOS to be an excellent tool for those times when you must have DOS.

A comprehensive list of resources for using networking under FreeDOS (and DOS in general) is available here.

FreeDOS boots and runs fine under Virtual PC, and is very handy for installing various operating systems.

:: GEM/3


GEM (Graphical Environment Manager) was a graphical environment created by Digital Research, Inc. (DRI) for use with CP/M. Subsequent GEM versions were compatible with MS-DOS, and were considered a low-cost alternative to Microsoft Windows. The advent of Windows 3.x took away most of MS-DOS users' interest in GEM.

When GEM/1 was released, Apple sued DRI because they were unhappy with the look-and-feel of GEM/1, which seemed to be almost an exact copy. This resulted in DRI changing GEM to make Apple happy.

GEM/3 installs and runs fine under Virtual PC. Note that it is rather finicky about the software diskettes being labeled exactly how they are "supposed" to be, otherwise the system would not install.

:: KA9Q


I first came across KA9Q in 1994, and was very impressed. KA9Q NOS (Network Operating System) was only the second known implementation of the Internet protocols for low-end computers. KA9Q could simultaneously act as a network client, a server and an IP packet router, including support for multiple client and server sessions.

The biggest laboratories during my undergraduate days at my school used to have a large number of PCs (1994-), and people actually used to trash the disks so that only those armed with bootable diskettes with DOS network can make use of them. A bootable diskette with KA9Q was real power back then!

KA9Q works fine under Virtual PC with any compatible version of DOS. Moreover, it is possible to get a suitable DEC 21x4x Ethernet card driver (for the network device that Virtual PC emulates), and have network connectivity from within DOS.

:: Novell DOS

Novell DOS

Novell DOS was a fully MS-DOS compatible operating system for workstations on Novell networks. It had enhanced memory management that allowed parts of DOS, device drivers and TSRs to be moved out of conventional memory on systems with an Intel 286 or later processors and extended or expanded memory. Novell DOS had support for preemptive multitasking and peer-to-peer networking, courtesy DOS Requester (a client that provided transparent redirection of printing and file accesses to a network server - handling layers 3, 4 and 5 of the OSI 7 layer model) and VLMs (Virtual Loadable Modules). Note that this is similar to Novell NetWare.

Novell DOS also had disk doubling compression, a disk cache, utilities for defragmenting and undeleting, and so on.

Novell DOS 7 boots and runs fine under Virtual PC.

:: OpenDOS


OpenDOS is an MS-DOS clone, including various MS-DOS utilities. If there were not enough DOS flavors and releases already, here's the most precise summary (ahem) of OpenDOS's history I could find (source): "Caldera OpenDOS (1997) is the successor of Novell DOS (1993-1996), which derived from Digital Research's DR DOS (1988-1993), and DR Multi-user DOS, which in turn were based on DOS Plus (1985-1987), CP/M-Plus, DR Concurrent DOS (since 1986), and DR Concurrent CP/M (CCP/M) (since 1982) families, directly going back to the legendary CP/M (1973) and the multitasking/multi-user version (MP/M)."

The current ownership of OpenDOS is explained by SCO on this page.

More information on OpenDOS can be found on the OpenDOS Unofficial Home Page.

OpenDOS boots and runs fine under Virtual PC.