IBM PC DOS 4.00 (06-17-1988)
Released in 1988 by IBM
For IBM PC and IBM PC Compatible computers.

This is the original release of PC-DOS 4.00. Bugs and all! It
includes two 720k disk images in raw/winimage format.

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.

Most current downloads out there claiming to be 4.00, are actually
4.01.

Do not confuse 4.01 with this version. IBM shipped 4.01 without
changing the "4.00" version IDs, either in the kernel, the command
processor, within the documentation, or even the exterior packaging.

As a result, there are only two ways to tell the difference between
4.00 and 4.01:

1: IBM's floppy disk label will read "Version 4.00" or "Version 4.01"
2: 4.01 will have some files dated 08-03-1988.

For more information about this version, see:
http://web.archive.org/web/20060618041734/http://16bitos.com/400ibm.htm

This site lists the bugs in 4.00 that were fixed in 4.01
http://www.retroarchive.org/garbo/pc/doc-soft/dos400.bug
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Readme file by ibmpc5150