While the IBM PC and its follow-up, the hard drive-based PC XT, were huge successes, the firm stumbled with subsequent models. The IBM PCjr, an ill-fated attempt to capitalize on the home market, was an outright disaster. And the IBM AT, IBM’s first non-8088-based PC, shipped in 1984 with an Intel 80286, a chip that Bill Gates had called “brain-dead.” He had advised IBM to wait for the more powerful and 32-bit 80386, which wouldn’t even be announced until a year later.
Worse, MS-DOS---or, PC-DOS, as IBM called it---had been quickly released to accommodate IBM’s rush schedule for the first PC in 1981 and the limitations imposed by its 16/8-bit Intel 8088 processor and its weird segmented memory model in which only the first 640 KB of system RAM was easily accessible. And just a few years later, DOS was having a hard time keeping up with the changes coming in subsequent 16- and 32-bit Intel chipsets.