There were also many incompatible 8086 machines before (and at the same time as) the IBM PC, including many that ran MS-DOS but had different memory layouts (e.g. without the 640k limit), different floppy disk formats etc.
IBM's machine had great market success and was trivially easy to copy, at least if you illegally simply copied their ROM too. IBM sued many such companies out of existence (including Exzel here in New Zealand.
But then Phoenix reverse engineered the BIOS -- easy as it was small, simple, and even badly written (compared to e.g. the large 64k very cleverly coded ROM on the Mac) -- documented it, including the bugs, and then had other engineers do a clean-room reimplementation of the BIOS.
At that point IBM couldn't touch them, as there were no custom chips used in their machine.
Then Compaq beat IBM to using the 80386 by seven months, and when IBM's PS/2 machines did appear they used a different BIOS, different and incompatible expansion bus, different keyboard and mouse connectors and video display.
The market basically ignored IBMs (expensive!) machines and copied Compaq and IBM lost control of the "PC".
People did adopt the PS/2 connectors (easy enough) and VGA, but otherwise continued with the same BIOS and memory map and "ISA" expansion bus until Intel did PCI 6 or 8 years later.
IBM's machine had great market success and was trivially easy to copy, at least if you illegally simply copied their ROM too. IBM sued many such companies out of existence (including Exzel here in New Zealand.
But then Phoenix reverse engineered the BIOS -- easy as it was small, simple, and even badly written (compared to e.g. the large 64k very cleverly coded ROM on the Mac) -- documented it, including the bugs, and then had other engineers do a clean-room reimplementation of the BIOS.
At that point IBM couldn't touch them, as there were no custom chips used in their machine.
Then Compaq beat IBM to using the 80386 by seven months, and when IBM's PS/2 machines did appear they used a different BIOS, different and incompatible expansion bus, different keyboard and mouse connectors and video display.
The market basically ignored IBMs (expensive!) machines and copied Compaq and IBM lost control of the "PC".
People did adopt the PS/2 connectors (easy enough) and VGA, but otherwise continued with the same BIOS and memory map and "ISA" expansion bus until Intel did PCI 6 or 8 years later.