A7A266: Mixing memory sizes?

[Paul Moloney]

My PC uses a A7A266 motherboard, which has two slots for DDR memory.
Currently it
has the following memory configuration:

512MB of memory (2 x 256MB) DDR SDRAM non-EEC 184 pin PC2100

The manual says:

"Install memory in any combination as follows".

Does this mean I can mix memory sizes? I'd like to replace one of the
memory sticks with a 512MB or 1GB stick, giving me either 768MB or
1280MB of memory, rather than having to replace both sticks.

Does this work? Has anyone else tried this configuration successfully?

Thanks,

P.
--
-pm

http://oceanclub.blogspot.com

"The sea was angry that day, my friends. Like an old man trying
to send back soup in a deli."

 

[Paul]

My PC uses a A7A266 motherboard, which has two slots for DDR memory.
Currently it
has the following memory configuration:

512MB of memory (2 x 256MB) DDR SDRAM non-EEC 184 pin PC2100

The manual says:

"Install memory in any combination as follows".

Does this mean I can mix memory sizes? I'd like to replace one of the
memory sticks with a 512MB or 1GB stick, giving me either 768MB or
1280MB of memory, rather than having to replace both sticks.

Does this work? Has anyone else tried this configuration successfully?

Thanks,

P.

Yes, it means you can mix memory sizes. The important thing is
to use all the same type of RAM. You probably know you cannot put
SDRAM and DDR RAM in the board at the same time. The manual
also mentions unbuffered and registered memory, and you cannot
mix those types either.

Have a look through Google, for comments about brand specific
issues, or problems with the board in general. A couple of posters
mentioned Micron chips didn't work well - but much has changed
over the last four years, in terms of chip characteristics.
(Different silicon die versions from every manufacturer...)

The cheapest combo you could get, is a couple of 512MB sticks.
At the 1GB size, there are the cheap "stacked" unbuffered 1GB
DDR DIMMS, and the more expensive proper unbuffered 1GB DDR
DIMMs based on 64Mx8 chips. The "stacked" ones place twice the
loading of an ordinary module, on the memory bus - that means
with a few exceptions, the memory controller will not be happy
driving them. If you buy your 1GB DIMMs from a name brand source
(Kingston, Crucial, CorsairMicro.com) chances are you'll get
a proper module - the generic unbranded stuff is the stuff to
watch out for.

You could buy some 512MB PC3200 CAS3 memory, and it is backward
compatible with PC2100. At PC2100 speeds, the memory will run
at CAS2, which is as good as you can do. The reason I mention
this, is PC3200 is much more common, and potentially cheaper
than some old PC2100 that has been sitting on some vendor's
shelf for a few years.

Also, if you are using Win98, you know about 512MB being the
largest totally trouble free memory size ? Between 512MB and
1GB, you have to mod a file to make it work (didn't work
stable for me until I dropped back to 512MB - it works
for some people). Using more than 1GB on Win98 won't work.

BTW - Does your AGP card work ? There was a poster "Dr Teeth"
looking for help a few days ago. If your AGP slot is really
working (texture transfer and all), perhaps you could give
him a few words of advice.

Paul

 

[Paul Moloney]

Yes, it means you can mix memory sizes. The important thing is
to use all the same type of RAM. You probably know you cannot put
SDRAM and DDR RAM in the board at the same time.

Yup, got that bit.

The manual
also mentions unbuffered and registered memory, and you cannot
mix those types either.

Not sure which mine is; hopefully it's labelled on the module.

The cheapest combo you could get, is a couple of 512MB sticks.

I was thinking of getting a 1GB module, and combining it
with one of my existing 256MB module (ensuring that everything
bar the size is compatible). Would 2 x 512MB be cheaper, or just
an option that's more likely to be compatible?

Cheers,

P.

 

[Paul]

Yup, got that bit.


Not sure which mine is; hopefully it's labelled on the module.


I was thinking of getting a 1GB module, and combining it
with one of my existing 256MB module (ensuring that everything
bar the size is compatible). Would 2 x 512MB be cheaper, or just
an option that's more likely to be compatible?

Cheers,

P.

To choose a name brand example:

http://www.ec.kingston.com/ecom/con...A266+Motherboard&distributor=0&submit1=Search

1GB PC2100 CAS2.5 $107..$180 (four stores)
512MB PC2100 CAS2.5 $ 48..$ 76 (five stores - one is OEM and warranty
will differ)

There is a Corsair Value Select 1GB for $90.
http://www.zipzoomfly.com/jsp/ProductDetail.jsp?ProductCode=80098-34

You'll notice on some of the descriptions on Pricewatch, that
128Mx4 chips are used on some of these cheap ($57) 1GB modules.
The $57 modules are not the ones I'd want to buy. The chips on a
1GB module should be 64Mx8 chips (see if your vendor even knows
how the modules are constructed - if there are heat spreaders
on the modules, you may get some kind of story that they
"don't know", which is not the right answer).

http://www.pricewatch.com/prc.aspx?i=33&a=5025

This is how a proper 1GB module is constructed. Sixteen chips
of type 64Mx8, eight per side of module:

http://www.valueram.com/datasheets/KVR266X64C25_1G.pdf

If I was going to buy a 1GB module, I'd want the ability
to return the module for a couple of 512MB modules, if
the 1GB module doesn't work out (plus whatever the difference
in price that exists on the day you do the swap). At these
prices, a restocking fee wouldn't be too much of an issue.

I guess my main reason for recommending 2x512MB is there is
just less risk in the transaction. If you actually know a
shop owner you trust, that may change the equation for you.
I've been burned a couple of times buying generic RAM that
went bad about a year later, so now I only buy name brand
stuff (last two orders were Crucial). There aren't enough
entries in Google, to make brand recommendations.

Paul

 

[Paul Moloney]

Paul wrote:
[...]

Phew! Thanks for all that, it's an education. Just one thing
I missed earlier - is memory _always_ backwards
compatiable? For example, is PC3200 compatiable with PC3000,
PC2700 , PC2400 and PC2100? Or is it only compatible
when explicitly stated?

Cheers,

P.
--
-pm

http://oceanclub.blogspot.com

"The sea was angry that day, my friends. Like an old man trying
to send back soup in a deli."

 

[Paul]

Paul wrote:
[...]

Phew! Thanks for all that, it's an education. Just one thing
I missed earlier - is memory _always_ backwards
compatiable? For example, is PC3200 compatiable with PC3000,
PC2700 , PC2400 and PC2100? Or is it only compatible
when explicitly stated?

Cheers,

P.

I have looked at the datasheets for the individual RAM chips,
and the specified clock goes all the way down to handle PC1600
rates. So, the answer is yes, they are backward compatible.
Without any statement from the vendor. At least, I haven't found
a datasheet yet that said otherwise.

The only time it is necessary to buy a specific speed of RAM,
is if you have a brain-dead BIOS design. There are some BIOS
setup screens, that have absolutely no options for controlling
memory. For some of those, you buy a PC2700 DIMM if you want to
force such a stupid motherboard to run at DDR333. In other
words, the SPD on the DIMM is used to "steer" the motherboard
where you want it to go, as the motheboard is permanently in
"Auto" mode. Which is a pretty pathetic way to do things, but
necessary for some of the microATX boards.

Paul

 

[Paul Moloney]

I have looked at the datasheets for the individual RAM chips,
and the specified clock goes all the way down to handle PC1600
rates. So, the answer is yes, they are backward compatible.

Cheers; in the end, I went for the following:

http://www.dabs.com/uk/channels/components/memoryandaccessories/productView.htm?quicklinx=30R1

1GB 184Pin DIMM PC3200 DDR Non-Parity CL2.5 memory

It's Kingston; judging from reviews is good quality and compatible
with my motherboard. If it doesn't work out in a 1GB + 256MB configuration,
I'l return it and go for 2 x 512MB. Ta for your help,

--
-pm

http://oceanclub.blogspot.com

"The sea was angry that day, my friends. Like an old man trying
to send back soup in a deli."