13 Sep
2005
13 Sep
'05
7:59 p.m.
On Wed, 14 Sep 2005 00:45:56 +0100 (BST)
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
The IBM PC (PC-1) had four banks of 4116 DRAM on the motherboard. The
first row was soldered in, the other three banks were optional. It was
called the 16/64K motherboard. My copy of the Technical Reference
Manual is from that generation, as it came with dad's 16/64 system. The
rest of the 256K was in the I/O channel.
Just to add more lore:
The floppy controller and floppy drive were very optional on the early
PC, and a rather pricey option. There was a cassette cable for less
wealthy users. And on any IBM machine up to the late XT era, if you
boot it up with no disk in the A drive or no floppy hardware at all
installed, it will boot into 'cassette basic'. (does anybody know if the
PC-AT had cassette basic resident in ROM?) My PC Convertable will do
so. Sadly, you can't save or load anything into 'Cassette Basic' on the
Convertable or models later than the PC as there's no cassette
interface. I wonder if anybody has ever 'back ported' the Cassette port
to an ISA bus card?? (not that it would help on the PC Convertable, of
course.
I remember a
little shop here in Santa Ana which had the first clone
of the IBM PC. It was a single board which had 640k memory, allowed
using 64k memories, instead of the 16K memory that the PC and XT
earlier models used.
DId any IBM PC/ST motherboards use 16K DRAMs. Yes, I know the standard
memory mapping PROM could be set up to use 4 rows of 4816s (64K o nthe
mainboard), but did IBM ever do that? There's no mention of it in my
TechRef.
The PC used
either EProms, (16K I think) and the Roms that were
shipped with the BIOS were registered. The standard Data I/O would
Do you mean there were internal data latches in the IBM ROMs?
not read them since they were not programmable,
and needed their
output enabled to read the data.
But once someone had them in the 2716's, it was easy to get them
running in your superboard.
Surely it was trivial to use DEBUG or similar to dump the appropriate
area of memory to disk...
First systems had a 63 watt P/S, and IBM cards if you could find
them for video. Also there was no floppy controller on the first
board.
AFAIK, no IBM PC, PC/XT, PC/XT-286, PC/AT, or PC-jr had a floppy (or
hard disk) contorller on the mainboard. None had parallel ports
either, and the PC-jr was the only one to have video and a serial port
on the mainboard.