The Mother Board

Hello

I recently got hold of an old AcerPower 486SX from an online seller and it didnt come with any manuals or nothing.
I really want to learn all there is about this machine and also find out the maximum amount of RAM and jumper settings.

There is no BIOS string to mention. All the diagnostics tools ive run states that it is an ACER-BIOS.

From what I can tell - the part number of the motherboard is 48.99401.001

For all the information I have please use my documentation site http://psybulon.azurewebsites.net/

the problem to find anything about ur PC is that Acer used to indentify his models/series with names so if U don´t know the name of Ur PC mopel is almost imposible to find something

on anyway take a look at:

http://www.cnetusa.com/support/manuals/cn5614rv.pdf

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Thank you for your reply.

The computercase is labeled AcerPower486SX
It also has a model no of MZ25D extension id 014
Fcc id GQ8MZ25D

All info found on the webpage i linked in my first post.

I have searched on almost all model ids, numbers, part numbers and ids i could find - without any luck as of yet.


The manual you linked is for a 56k modem and of no use to me.

The first video screen you see will have a string of characters at the bottom lower left corner. This is the BIOS string, a positive ID of the system, BIOS version and date of inception. Also identifies the board model.
Most older 486 boards had only ISA slots, or ISA/VESA slots. Newer models may have ISA and PCI slots.
More info on what the board looks like would be helpful.
What socket version is on it?
How many memory slots and type (30-pin, 72-pin)?
Groups of jumper blocks here and there, to set either SX or DX type CPU?
Should be small printed diagrams with jumper settings and FP connections.
Only one IDE (hard drive) port or two? Or none?
The older 486 boards could accept either 1 Mb or 4 Mb SIMM memory. Newer models might accept 16 MB 72 pin SIMMS.
The memory type should be non-ECC, or unbuffered.. around 100ms speed.
May be some info in this link..
http://www.kahlon.com/rm5794_Acer_AcerP ... 466dv.html

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Thank you.
Please check my software diagnostics part on the website i linked in my first post.

No bios string other than ACER-BIOS.
There is 4 ISA slots.
3 72pin Simm slots and 2mb onboard memory
I Do not know what the socker is called. Im guessing its an 486 socket. Please see motherboard pictures (There is like 16 of them) on the site

Excellent montage of images and info!
From what I see in the main image of the motherboard, that 2 MB of memory you note is likely for on-board video, expandable. The long black contact header next to it is for a "feature" addition.
For the three main memory slots, note on the right side.. Bank 1 is empty, Bank 2 and Bank 3 are filled. Bank 1 should have a module there. This is true for 99.9% of designs, but there are a few that use a different order.
As to the 486 socket type, check these links for comparing..
http://anwarbari.tripod.com/bcm/cousewa ... _Types.htm
http://www.informit.com/articles/articl ... &seqNum=15
The oldest socket types had no release lever for the CPU pins. Newer types have a release lever, and are called "ZIF" sockets or zero-insertion force. A very thin special "fork" was needed to remove the CPU from a non-"ZIF" socket.

_________________
F@H.. to solve mankind's maladies.. in our lifetimes!

Thank you for your informative reply.

The 2MB memory is actually onboard RAM. I have two 8mb sticks that bios recognizes as 4mb each and all memory analysis software and also the memory check in the beginning reports 10mb.
4+4+2.

I dont have another 8mb stick of the same type to place in bank 1 - however I am waiting on 3x4mb sticks to see if i can get at least 14mb of ram 4+4+4+2.

There is no L2 cache present, and i would like to get a stick to put in the "CACHE SOCKET" port on the motherboard - any info on that?

The socket is not a zif-socket. I have not tried to remove the cpu. The computer works fine, i just want to know everything about it

The cpu is from what i note clocked at 100mhz, so it seems to be a tiny bit overclocked (should run at 75?)

You are noting that each memory module is actually 8 MB but is recognized as only 4 MB?
Or the modules are 4 MB each, total 8 MB?
Yes, some brands did have a bit of on-board main memory. A carry-over from the 8088 age where 1 MB was maximum main memory.
Older systems such as this use only single-density memory types. Double-density would not be recognized for what they are.
Single density refers to one layer of memory pages.. double density refers to two layers of pages, stacked like a sandwich.
There are some 20 pin DIPP chip sockets at the upper corner of the board image.. that should be the on-board cache memory.
There is some cache memory on the CPU die, but external cache memory is on the board. Typical external amounts are 128KB, 256KB or 512KB. The on-die cache may be only 32KB. Finding additional cache memory for this older board may be near impossible.
The CPU has the marking "486ODPR75" on it.. indicating it is rated at 75 MHz max speed. Perhaps the diagnostics program does not truly recognize the true speed.
There are two Web sites which may have more info about this board.
http://stason.org/TULARC/pc/motherboards/
http://www.elhvb.com/

_________________
F@H.. to solve mankind's maladies.. in our lifetimes!

Correct, the sticks are 8mb but only recognized as 4mb. They are not double-stacked from what I can tell. And there is only ICs on one side of the memory (please see pictures on my site - first post link)

The sockets in the upper left seems to be for expanding the GPU memory. It is stated to be 512k and also expandable with another 512k.

However the unsoldered memory locations near the CPU seems to be where some revisions of this board had its L2 cache.
There is no L2 cache on this board, only the 16kb L1 present in the CPU.

Maybe the cache socket is my only way of getting more cache. Hope i get hold of it some day.


Thank you for your website tips, I will try to find motherboard information there.

Without a proper manual, 'guesstimating' may not be accurate. Each manufacturer has their own motherboard design, to avoid copyright infringements.
Did check the FCC ID number, and looks to be around 08/92 license granting for the design.
https://fccid.io/GQ8MZ25D
The memory chips on the modules have "SEC KM48C2100AJ-6" on them. Made by Samsung Corporation, each chip is 2 MB x 8.
The last digit is the maximum bus speed. So indeed each module is 8 MB @ 60 ns.
http://www.datasheetarchive.com/KM48C21 ... sheet.html
The ID on the memory modules in the 2 MB area is "HM514900JP8" which indicates made by Hitachi, 80 ns speed, and being 4 chips, only 512KB each.
You may be able to use 8 MB modules on that board, but the memory has to be single-density type.
Being single-sided or double-sided does not designate the density of a memory module.

_________________
F@H.. to solve mankind's maladies.. in our lifetimes!