[trollbridge]

ROM BASIC on the IBM PC was humongous for its time (32KB). The ROM BIOS itself was only 8KB.

Considering DOS 1.0 was under 12KB, it would have probably been useful if they'd put disk I/O routines in the ROM... except it would have been rapidly obsolete since DOS 1.1 already had a different disk format (for double sided disks), and then DOS 2.0 changed it again (9 sectors per track instead of 8, and subdirectories).

Note that the BASIC interpreters on those early machines mostly used the ROM. The disk BASIC interpreter was only 10K (and an "advanced" version was 16K), so you could run DOS and BASIC with the ability to save files to disk on a machine with 32K of memory. Not that anyone back then ever bothered to do this, but RAM seemed expensive when they designed it in 1980.

DOS in ROM was an idea that kept being tried but never really caught on, even though with the right design it would make for a significantly faster system.