Which operating system IBM customers would choose was at first uncertain.
Although the company expected that most would use PC DOS IBM supported using CP/M-86—which became available six months after DOS—or UCSD p-System as operating systems.
IBM promised that it would not favor one operating system over the others; the CP/M-86 support surprised Gates, who claimed that IBM was "blackmailed into it".
IBM was correct, nonetheless, in its expectation; one survey found that 96.3% of PCs were ordered with the $40 DOS compared to 3.4% for the $240 CP/M-86.

The IBM PC's ROM BASIC and BIOS supported cassette tape storage.
PC DOS itself did not support cassette tape storage.
PC DOS version 1.00 supported only 160 kB SSDD floppies, but version 1.1, which was released nine months after the PC's introduction, supported 160 kB SSDD and 320 kB DSDD floppies.
Support for the slightly larger nine sector per track 180 kB and 360 kB formats began 10 months later during March 1983.
Which operating system IBM customers would choose was at first uncertain. Although the company expected that most would use PC DOS IBM supported using CP/M-86—which became available six months after DOS—or UCSD p-System as operating systems. IBM promised that it would not favor one operating system over the others; the CP/M-86 support surprised Gates, who claimed that IBM was "blackmailed into it". IBM was correct, nonetheless, in its expectation; one survey found that 96.3% of PCs were ordered with the $40 DOS compared to 3.4% for the $240 CP/M-86.
The IBM PC's ROM BASIC and BIOS supported cassette tape storage. PC DOS itself did not support cassette tape storage. PC DOS version 1.00 supported only 160 kB SSDD floppies, but version 1.1, which was released nine months after the PC's introduction, supported 160 kB SSDD and 320 kB DSDD floppies. Support for the slightly larger nine sector per track 180 kB and 360 kB formats began 10 months later during March 1983.
IBM Personal Computer