30 Sep
2001
30 Sep
'01
5:19 a.m.
On early IBM machines, ROM Basic was entered by
performing an INT
18h instruction. On machines not implementeing ROM Basic, calling
int 18 would simply display the "no rom basic" message, often in 40
col mode since that was the lowest resolution suupported.
Many bootstraps terminate with a call on Int 18 to indicate the absence
of bootable code on the media hence the message would appear.
It's been a while since I powered one up, but since the IBM
PCjr's BASIC ROM is on a cartridge vice on the mainboard, what do you
get if you boot the machine with neither a DOS floppy or the
cartridge BASIC inserted? Were there other IBM PC's that didn't have
the BASIC ROM on the mainboard?
Jeff
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