P2B rev 1.02 - suports 512MB mem. cards ?

[Steve]

Hi, Is it a BIOS restriction that prevents you using larger capacity
Memory cards on the Asus P2B m/b ? I've got the beta 1014 release and
can only use a max mem. module of 256MB, the 512MB Modules register as
128MB ! If it is a BIOS restriction... has anyone revised it to handle
512MB cards ? If not, anyone in Asus willing to give out the source, or
take the challenge ?



Regards


Steve

 

[Paul]

Hi, Is it a BIOS restriction that prevents you using larger capacity
Memory cards on the Asus P2B m/b ? I've got the beta 1014 release and
can only use a max mem. module of 256MB, the 512MB Modules register as
128MB ! If it is a BIOS restriction... has anyone revised it to handle
512MB cards ? If not, anyone in Asus willing to give out the source, or
take the challenge ?

Regards

Steve

It is a hardware restriction. It is how the Northbridge addresses
the memory that places this limitation on memory type. A BIOS
isn't going to fix it. (If you Google for other brands of
motherboards that use the 440BX chipset, you'll see they have
exactly the same problem.)

I've used 4x256MB on my P2B-S (at 100MHz) and that works fine.
I got my 256MB modules from crucial.com, as they have the right
type for the job. There are "high density" 256MB modules and
"low density" 256MB modules, and the difference between them
is the size of the memory array (in rows and columns).

To illustrate the concept, say you wanted to make an array of
16 million objects. You could arrange them 4096x4096 or
8192x2048 and so on. If representing those numbers in binary
arithmetic, 4096x4096 takes 12 bits for each number. The
8192x2048 case takes 13 bits for the first number, and 11 bits
for the second number.

Now, say you had a piece of hardware with just 12 output lines
on it. The 12 output lines could be used to successfully access
all 16 million locations of our 4096x4096 test array. If
we connect our 8192x2048 array to the 12 lines, one of the wires
on the 8192 side of the array is unconnected, because it has
13 inputs. That causes half of the locations in the array to
be inaccessable.

That is what is happening to your 512MB DIMM. Not enough
address bits to drive all of the memory array. A similar
problem can even happen if you use a "high density" 256MB array.
If buying 256MB sticks, you should ask your vendor if they
understand this issue, and whether the sticks they are
selling are the correct type.

This is all explained in one of Roland's FAQs. See, for example,
"What module sizes are supported on my bx-based board?"

http://homepage.hispeed.ch/rscheidegger/ram_bx_faq.html

The FAQ says 16 ram chips, each chip organized as 16Mx8, is
the correct type for a 256MB module.

If you look on the Crucial web page, there are no 512MB modules
listed for the P2B. Crucial does carry 512MB modules, but won't
list them for a 440BX based motherboard.

http://www.crucial.com/store/listpa...erboards&mfr=ASUS&cat=RAM&model=P2B&submit=Go

HTH,
Paul

 

[Rick]

Hi, Is it a BIOS restriction that prevents you using larger capacity
Memory cards on the Asus P2B m/b ? I've got the beta 1014 release and
can only use a max mem. module of 256MB, the 512MB Modules register as
128MB ! If it is a BIOS restriction... has anyone revised it to handle
512MB cards ? If not, anyone in Asus willing to give out the source, or
take the challenge ?

It's a chipset limitation, not a bios restriction. The BX chipset
can see a max of 128MB per logical bank, and each dimm
slot is limited to two banks (therefore a max of 256MB for
each dimm).

 

[gerry]

Hi, Is it a BIOS restriction that prevents you using larger capacity
Memory cards on the Asus P2B m/b ? I've got the beta 1014 release and
can only use a max mem. module of 256MB, the 512MB Modules register as
128MB ! If it is a BIOS restriction... has anyone revised it to handle
512MB cards ? If not, anyone in Asus willing to give out the source, or
take the challenge ?

I've got a gig on a newer box and it doesn't get used much. The 512M
I've got on my P2b seems to get the job done

If you need more than 512M on a P2B, you probably really need a newer
box as the BX memory bus is soooo slow.

Building my new box last year, I realized it was long overdue to put
the sacred cow out to newsgroup/email pasture.

 

[ares]

I recently got a decent deal from KomUSA on a 256 mb low density chip that
actually works(most seem a bid pricey); got one once for $20 that wasn't the
right density and it would only read as a 128 mb.
ares

 

[Montana Pete]

It's the architecture of the simm. Some will read one side so you only
get 256MB, but I have never seen a 512 read 128. Anyhow, you need low
density simms. Now I suppose you could decompile the bios, rewrite the
code, and reflash the bios, and if there is no hardware restriction
then with only $1000 worth of effort you can save spending $25 for a
low density 256MB simm. While you're at it there is a 750MB
restriction on the memory capacity so you might want to change that
too.

 

[ares]

Yep, I know the 750 max; how can something like that be changed? I meant
also that my 256 mb read as a 128.
ares

 

[Steve]

I've finally got the full complement of 768 MB of memory, 256 MB x 3.

Getting there however wasn't quite as painless as I'd thought it would be.
After the failure with the 512MB module, I then decided to just stick to
256MB modules, I and purchased Samaung 256MB modules ( M377S3320BT3-C1H )
bad news, they didn't work. I think the reason was the revision of SPD used
since they were of type PC100-322-622R whereas the Asus board only seems to
handle PC100-322-620R - well thats' the type that worked - having tried one
I pulled from another machine... finally bought a couple of Compaq 256MB
modules with PC100-322-620R stamped on them, I found to my delight that they
worked.

The following link explains (briefly) the PC100-343-620R code:

http://www.sisoftware.co.uk/?dir=qa&location=det_mem&langx=en&a=