The IBM pc (5 slot) motherboard comes with 6 rom sockets for rom (bios rom)
software. Usually, these are filled with 5 roms which provide about 40K of
bios software & ibm cassette basic. The chips used are actually m-roms (or
proms) and are 8Kx8 in orientation. However, unlike common 8Kx8 (2764...)
roms which have 28 pins, these only have 24 pins. Because the programming is
'written' into the roms at the time of manufacture, there is no need for
programming or erase pins, allowing a more dense design.
The later IBM bios roms provided support for several different keyboards and
options that eariler models didn't. IBM never provided rom support for high
density floppies in these roms. Users who wish to upgrade to these drives
have been forced to use a variety of measures, all of which have drawbacks....
I find the keyboard support (of lack thereoff) in the roms the MOST annoying...
This posting is intended as both helpful information for people who wish to
upgrade these systems, or as background reference information. I have been
upgrading these systems extensively using Intel Inboard pc 386's and strongly
believe that this can be a very cost effective approach.
There are several approaches that can be taken to upgrade the rom info....
1. Find/buy a broken/abandoned motherboard with later ibm roms. If the ibm
roms have a single date (1981) on them, they are a older set and what we
want to dump due to lack of common keyboard support. If the roms have 2 dates
on them 1981,1983 then they are a later set which has better keyboad support.
Simply move the chips (in order) from 1 motherboard to the other.
2. Buy a second manufacture's PC bios upgrade kit. UPGRADES ETC. INC, 15251
N.E. 90th Street, Redmond, WA 98052, fax(206) 881-8294 & 1-800-955-3527
(206) 882-3634 (outside the U.S) has, PHEONIX-IBM-PC BIOS for $79.95 (u.s.)
These roms probably also have high density floppy support in them, and more
than likely, use of them will preclude the use of IBM Basic or cassette basic.
3. Find a source (now very scare in my opinion) of the IBM Bios Rom UPGRADE
kit. The last of these I saw were like $30, but have long since disappear-
ed. If anybody knows of a source remaining for this, feel free to let me know.
These 3 options have been (basically) the only available documented methods I
have been able to find. I'll add a couple new methods for the brave of heart.
4. Jameco Electonics, 1355 Shoreway Rd, Belmont CA 94002, (415) 592-8097
or fax (415) 592-2503, sells AWARD BIOS upgrade kits for the ibm XT and
most clone xt's. part No. 88Bios for $24.95. (quite a difference from $79.95).
HOWEVER, these are intended for standard 28pin 2764 8Kx8 sockets, NOT the
24 pin 9264 8Kx8 sockets found on the PC. With a little imagination and hand
crafting, these chips can be modified to work in with the ibm PC motherboard.
This upgrade kit wil also preclude the use fo IBM basic & cassette basic, and
do provide rom support for high density floppies.
5. If you already have a later ibm PC bios set (identified above...) & aren't
too worried about going to jail for stealing ibm bios software in order to
upgrade your ibm pc (and it's doubtful ibm would convict you as long as you
weren't in business, and they aren't selling this product or even supporting
it with upgrade parts anyway....). If you have access to a rom burner, you
can use the info provided to copy the bios rom software from the 9264 s-roms
onto standard 2764 roms, and then modify the 2764's for the ibm pc motherboard.
I hope that if you have a rom burner, you are sufficiently inclined to see that
a special 'socket' must be made in order to be able to read the 9264 just like
a standard 2764. The 2764 chip modifications provide the functional schematic
for making such a socket. See below....
MODIFYING THE 2764 ROM FOR USE IN A 9264 (IBM PC ROM) SOCKET.
Bend pins 1, 20, 26 & 27 straight out from the chip body and carefully cut the
lead pins off flush with the chip body, being careful not to loose or damage
the lead pins (we will need them shortly). Using wirewrap wire (or some other
small insulated wire), carefull solder short wires onto the lead pins we just
cut off. Be careful to keep the solder and wire very close to the end which
was cut and away from the narrow end which goes into the socket. Take your
IBM motherboard, (if still in a system, remove all the cards from the system
as well as the drive in the 'center' bay (if desired) in order to open up room
to work on the motherboard.) I'm assuming that you can properly identify the
bios roms on the motherboard and have a basic hardware understanding of the PC,
if not, I recommend getting a book and reading up (this probably isn't for you
anyway, and I recommend getting help before now anyway....). Back on the
bios upgrade (2764) chips, (the same thing needs to be done for both chips)
carefull bend pins 20 & 23 out a slight amount so they are out of line with the
other lead pins and won't enter to socket (and go outside the socket). Take
another wire wrap wire, carefull wrap it around pin 20, and run it over the
top of the chip, and then wrap it around the very base of pin 14, so pin 14
will still seat firmly when the chip is installed. The ends of the wirewrap
wire will need to be carefull striped of insulation if you aren't using either
prepared wire or a board level tool. Now, take the second bios chip of the
pair, it will go in the second socket on the motherboard for roms from the
drive bay/power supply side of the motherboard (nearest the 8088). Take the
first wire & lead pin combo you made, and insert it into pin 18 of the rom
socket, seat it fully using needle nose pliers, then carefull bend the exposed
lead down so it sits flat on the top of the socket (towards the center of the
chip socket). Repeat this with socket pins 21 & 24. I recommend routing the
wire, so the one from 18 goes out of the socket at the 14/15 pin end (front
of the system) & the ones from 21 & 24 to the 1/24 pin end. Insert the second
2764 bios rom chip into the socket, so that pins 1,2 & 27,28 are hanging out
of the socket in free space. Wrap the wire from pin 18 of the socket around
pin 23 of the chip (which has been previously bent so it won't enter to socket)
being careful not to encroach into the area needed for the neighboring chip
or another exposed lead/contact causing a short. Take the wire from pin 21 of
the socket and wrap it around pin 2 of the chip, then the wire from pin 24
to pin 28, taking the same precautions mentioned before.
Repeat this procedure with the first chip in the bios upgrade pair, (when
using the award bios upgrade or some other 2 chip set), using the next socket
towards the power supply/drive bays. If copying the entire PC rom set from a
later motherboard, I recommend starting with the chip farthest away from the
powersupply/drive bay area to provide max working room. I also would be most
easiest accomplished if the motherboard was NOT installed in a case, but it
can be done either way.
As always, I renounce all claimed warranties, and this information is
provided as a educational service only. Whatever you decide to do is up to
you and you alone. Also as a educational aid, I will try to field problems
and questions as time allows and to the best of my ability via email @
amic...@sunrise.acs.syr.edu via internet
amic...@sunrise.bitnet via bitnet
Here's part of the doc file:
From: Ya`akov Miles <multi%dac.triumf.cdn%ubc.csnet at RELAY.CS.NET>
To: Info-IBMPC at MIT-MC
Re: BIOS Musings
You may be interested in a history of where this BIOS came from, and
how it arrived in its present form. A heavily patched,
partially-functionally BIOS (with no copyright statement, or other
visible indication of origin) was supplied with my IBM-PC/xt
compatible 10 mHz motherboard. In order to get my motherboard to
function correctly, in other words, to work with the parity interrupt
enabled and to operate with the NEC "V20", it was necessary to
disassemble and thoroughly go thru this "anonymous" bios, which was
hinted as supplied by Taiwan, while limping along on a name brand
bios, as supplied on my previous motherboard by a different vendor.
Copying IBM ROM chips for use in a clone, or for sale, would be a quite