1M to 2M revisited...

[C M Votava]

In article <8570002 at eecs.nwu.edu> morrison at eecs.nwu.edu (Vance Morrison) writes:

>I have some friendly advice for those interested in upgrading the
>motherboard ram.  It is not as easy as plugging in the ram chips.
>I have the schematics and after looking them over carefully the
>upgrade would require installing some resistor banks (33 ohm) and some 
>2 - 1 multiplexers as well as some cuts and jumpers and even THEN
>I am not sure that the software will pay attention to it.

Well, actually upgrading the motherboard from 1M to 2M is not too bad. Vance
is correct when he says that you don't just plug in the ram chips, but it's
not much harder. The resistor banks and multiplexers he mentions sometimes
already exist on some motherboards, for others, you can buy them at your
favorite electronics store. Here is the proceedure for upgrading a motherboard
from 0.5M to 2.0M that was posted a number of times in the past:


Fri Feb 19 13:59:54 CST 1988
This proceedure has been confirmed. -- cmv

/* Written 10:16 am  Jul 13, 1987 by looney!cmv in ihlpm:unix-pc.general */
/* ---------- "7300 Motherboard upgrade proceedure" ---------- */

Here is a proceedure for upgrading the motherboard on
a unix-pc. Do not follow this proceedure unless you KNOW WHAT YOU ARE DOING!
If you trash your motherboard, only YOU can be responsible for the damage!
The text of this proceedure was, at one time, in an official document, it has
since been dropped.

256K BYTE RAM CHIP UPGRADE

Memory on the processor board and on the memory expansion board may be expanded
from 512K bytes to 2M bytes. This is accomplished by installing 256K byte RAM
chips in place of the original 64K byte RAM chips.

UPGRADING THE PROCESSOR BOARD

- There are seventy-two MB8264 chips located on the processor board. These
are 150nsec, 64K byte RAM chips manufactured by Fujitsu (the RAM chips used in
future machines may be provided by another vendor due to the laws of supply and
demand). These chips are illustrated in the schematics on sheets 19 thru 22.

These chips will have to be removed and replaced with the appropriate 256K
byte RAM chips (for example, MB81256-15).

- After the 256K byte chips have been installed, memory size has quadrupled.
Two more address bits will be required to access this extra memory, therefore
another address MUX is needed.

(sheet 18) A 74F258 Multiplexor chip must be installed at board location 13B.

- Jumper JR1 (sheet 18) is located at the front of the processor board, to the
immediate left of the chip in position 12A. When 64K byte RAM chips are being
used, it is jumpered E2-E3.

With the installation of 256K byte RAM chips the E2-E3 connection should be
opened and re-jumpered E1-E2.