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#11
Yep. The early IBM machines such as the PC, XT, AT and XT-286 all had BASIC built in to ROM so the machine didn't need any disk drives or cassette to be able to boot to a command prompt, which technically meant that no OS was needed. However, without an attached cassette there was no way for the ROM BASIC to save and retrieve programs so you would need to type them in each time which wasn't particularly useful. The ROM BASIC also couldn't access a disk drive, in order to do that you needed to boot DOS and run BASICA from the DOS disk.