A comparison... RAM ADDRESSING / SIZES
> fixed 64 K
RAM on board (instead of 128 K on board of PC-100 B)
> a maximum of 832 K
RAM -with RAM extension board - (instead of 896 K on 'B')ROM
> ROM 04.03.11 (for PC-100-A) in 3 chips (type 2764) FA000-FBFFF (E89)
> PC-100B / PC100B+ has ROM 05.03 in 2 chips (type 27128) at memory addresses: F4000-F7FFF
FC000-FFFFFROM DIFFERENCES (derived from my latest ROM disassembly)
(*) PC-100-B only. Not present in original PC-100 specification from March 1983.
0x1a and beyond are marked as 'reserved' there.
There is no documented way to emit bell sounds on the Rainbow 100-A (confirmed in Jeff Armstrong's blog). No hardware limitation of course: the beeper sits in the keyboard.
$1f23 - (*) ROM_RomVersion 0x1a /* DX,BP<-offset,seg of 8-byte buffer */
$1f66 - (*) ROM_ChangeVectorMap 0x1c
$1fc2 - (*) ROM_RingBell 0x1e
$1fc8 - (*) ROM_GetSet7or8 0x20 /* AH<-function (1=get, 0=set); */
/* AL<-value (0=8, 1=7) (set only) : */
/* value->AL (get only) */
The 'A' model did not come with a hard disc, and there were no provisions in the old ROM to boot from HD directly.LIMITS WITH OPTION BOARDS
GRAPHICS (when using uPD7220 Graphics option)
> limited graphics palette: 4 colors where with the B board you get 16.
80286 ACCELERATOR BOARD
> Suitable Solutions 286 accelerator board runs in either a 100B or a 100+, but not a 100A.Note that i own neither a 100-A nor the fancier option boards. I am also more into software than hardware. Feel free to correct me.