Newsgroup: it.comp.hardware.cpu
Titolo: Trying to figure out what  RAM I should get

Bought Acer Aspire T180-I97Z. As the dealer offered a bundle deal with
additional 512mb ram at discount opted for it. When the RAM arrived it
was total mismatch int tems of module fitting in the socket.
Looked up Kingston website to decide which one to buy as Acer help was
going round and round about it without saying which one.
Kingston gives
D6464G50 512MB DDR2-800 DIMM
&
D12864G50 1GB DDR2-800 DIMM
I believe the significant here is DDR2-800 DIMM. This must match the
sockets in the PC.
What puzzels me is "Comments : MODULES MUST BE ORDERED AND INSTALLED
IN PAIRS for Dual Channel mode".
Does it mean that if I have 512mb RAM I need to buy another 512mb RAM
before going for 1GB RAM?
And even then I need to put 2 additional 1GB RAM? Making it a total of
3gb RAM?

 wrote in message 
news:1175196819....@n59g2000hsh.googlegroups.com...
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Look it up on 
www.crucial.com

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The T180 looks to be some kind of desktop. The info here shows four slots.
http://www.crucial.com/store/listparts.aspx?model=Aspire+T180
Memory matching can be at two levels. You would need to know more
about the chipset, to know what options might be supported.
The tightest matching, is matching the pairs of DIMMs. For example,
if you wanted a total of 1GB of memory, you would buy two 512MB DIMMs.
The DIMMs in that case, have to match "rows, columns, banks, and ranks".
In terms of memory chips, each memory chip has a size, like 32M x 8, and
in that 32M address space, it takes a certain number of row and column address
bits, to address the memory. Inside the RAM chip, there are multiple
"slabs" of equal size, stacked along the Z axis, and that third dimension of
addressing is called banks. Finally, at the DIMM level, there are ranks (and
to save time, a sloppy incorrect definition would be single and double
sided DIMMs are single rank and double rank respectively).
So, if the chipset was an older one, and needed matching at that level,
you don't have to match the DDR2-800 or the 5-5-5 part, but if the
existing module was 512MB and single sided (8 chips), you'd want the
second DIMM to be 512MB and single sided (8 chips) as well. When there are
timing differences, like one stick is DDR2-533 4-4-4-12 and the second stick is
DDR2-800 5-5-5-12, the BIOS picks the highest common denominator for the
sticks, so the pair would both run at DDR2-533 4-4-4-12 perhaps. The extra
speed of the DDR2-800 stick might not get used, because the DDR2-533 might
hold it back, practically speaking.
Newer chipsets try to match the quantity of RAM on a per channel basis. For
example, you could have a 512MB and a 256MB on one channel, and a 256MB and
a 512MB on the other channel. The "DIMMs across from one another" are not
matched. What the chipset does in that case, is feed the channels independent
commands, or else it disables certain interleaving or page opening/closing
options, to make it work. Generally speaking, this doesn't really influence
the end user's RAM selection process that much, because for the most part,
it still means at least matching the sticks on a size basis. But what it
could mean, which is significant, is you could mix a 512MB single sided DIMM
with a 512MB double sided DIMM, and the chipset could still run in dual
channel mode.
Finally, if you fail to match the sticks well enough to enable dual channel
mode, all is not lost. Most modern chipsets will run in virtual single channel
mode, accessing one stick at a time. The user still sees the same total amount
of memory, and the only impact, is a reduction in memory bandwidth. Some
people, who did a poor job selecting memory, are blissfully unaware they even
made a mistake. So if you get it wrong, the operation of the computer is
seamless, and the computer won't make a big stink about it.
There are some older chipsets, where the motherboard will be quite upset
if the DIMMs don't match, and the computer may fail to post. But it sounds
like your computer is pretty new, so I'm guessing that is not going to happen.
So to know exactly how picky the computer is going to be, you'd want
to find out what chipset is used. You could use a utility like CPUZ,
or Everest, to list the chipset number. Based on the number, then you
could look for more info. Some chipsets have more info available for
them than others - and in a pinch, you can always track down a retail
motherboard's downloadable user manual, to get more help with how to
match memory.
But at the very least, even without any more info about the computer,
I'd try to match the sides and number of chips on the module. If the
existing DDR2 stick is 512MB and double sided, I'd try to find
another double sided DIMM with the same number of chips on it,
as a partner for the existing DIMM. Then pray that the BIOS does
not have a problem handling the selection of a compromise clock
speed and timings. That is because, it might be a lot of work, to find
a stick that matches size and ranks, as well as clocks and timings.
I'm really surprised the user manual for the computer, doesn't say
a few words about the memory. Many motherboard manuals usually
have a short sparse section on population rules for memory.
HTH,
      Paul

 a few words about the memory
Ditto.  BTW, Paul, thanks for a useful post.

 wrote in message 
news:1175196819....@n59g2000hsh.googlegroups.com...
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 Yes.
Wrong as usual.
Running in dual-channel mode may help performance, but it's not required.
How many pieces of memory are in the unit right now?
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jos...@gmail.com
 wrote:
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question how mush ram do you need?

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Doing a little checking, as near as I can tell, the T180 has a
Sempron processor, and is likely socket AM2.
The Acer site doesn't have a downloadable manual for the T180 yet,
so I cannot look at that.
The Sempron processor has the memory controller inside the processor.
Which means the chipset used on the Acer motherboard is irrelevant
to the behavior of the memory.
If I try and track down the info on the AMD site, the 32559.pdf
document "BIOS and Kernel Developers Guide" has some info on
how the memory map corresponds to the chip select signals on the
processor. What is missing though, is doc 31117.pdf, which would
have given a pinout of the processor, and allowed figuring out
what signals were actually available on the processor. That document
is apparently only available under NDA, which is stupid seeing as
previous S939 and S754 processors were downloadable.
So the only other thing I have to go on, is an Asus M2NPV-VM motherboard
manual. (I think M2NPV-VM uses the same chipset as the Acer T180, which
is why I selected that manual.) That manual claims, for socket AM2, that
the less strict matching rules apply.
    "Memory configurations
     You may install 256MB, 512MB, 1GB, and 2GB unbuffered ECC/non-ECC
     DDR2 DIMMs into the DIMM sockets.
     - For dual-channel configuration, the total size of memory module(s)
       installed per channel must be the same (DIMM_A1 + DIMM_A2 = DIMM_B1
       + DIMM_B2).
     - Always install DIMMs with the same CAS latency. For optimum
       compatibility, we recommend that you obtain memory modules from
       the same vendor.
     - Due to chipset resource allocation, the system may detect less than
       8 GB system memory when you installed four 2GB DDR2 memory modules.
     - This motherboard does not support memory modules made up of
       128Mbit chips or double sided memory modules using x16 chips."
Now, of that information, I don't know if Sempron supports ECC or not,
or Sempron supports 2GB modules. (The Crucial site lists max memory as
4GB, or 1GB per slot for the T180.) With the lack of info on the AMD site,
it is pretty hard to verify that part. There is a good chance that the
"less strict" matching rules mentioned above, would still apply to
Sempron.
I don't know what to make of the suggestion that the modules should have
the same CAS latency. The BIOS should just use the slowest timing of
the lot.
So, if you currently own 512MB, you could buy another 512MB module so
both channels have the same amount of memory. If you wanted even more
memory, you could purchase 2 x 1GB more memory, for a total of 3GB.
You would install 512MB + 1GB on one channel and 512MB + 1GB on the other
channel, and as long as the total memory was the same, chances
are it would still work in dual channel mode.
If the new 512MB module you purchased, had the same number of chips as
the original one, I would think, so much the better.
If it was my machine, I'd probably just pull the 512MB stick, and
install 2 x 1GB. And not bother buying a matching stick for the
existing 512MB one. I guess it all depends on how much money you
have to spend on this project, as to whether you go with 2x512MB,
2x1GB, or (2x512 + 2x1GB). With an OS like Vista, more is better,
at least according to this:
http://www.anandtech.com/showdoc.aspx?i=2917&p=3
    Paul

 How many pieces of memory are in the unit right now?
One 512mb piece.
Having read Paul's advice I shall try to get another piece exactly
same.
I believe though different mnufacturer should not pose any problem.

     Paul
A slightly different issue.
On a machine with Gigabyte GA-686BX motherboard I bought
http://www.crucial.com/uk/store/partspecs.aspx?imodule=CT64M64S4D7E
At the time of buying it I only thought of it fitting in the socket.
Few days back Crucial Support wrote to me that I had not bought wrong
memory.
When I look closely at the motherboard specification
http://www.giga-byte.co.uk/Products/Motherboard/Products_Spec.aspx?ProductID=1453
maximum capacity it supports is 256mb piece.
So it looks I was wrong in getting 512mb piece.

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If you look here, the largest stick listed is 256MB. That is the same
size that I used on my 440BX board (P2B-S).
http://www.crucial.com/store/listparts.aspx?model=GA%2D6BX+%28686BX%29
And the 256MB module has to be carefully selected. It has to have
16 chips (that kind of 256MB is termed "low density"). There are also
sticks for sale, 256MB in size, but they have only 8 chips on them.
They are called "high density". A stick with 8 chips, would not work
properly on the GA-686BX or on my 440BX motherboard either.
Actually, I've noticed a strange problem on my P2B-S. If I install three
or four of the 256MB low density sticks, my computer will freeze. If I
install two of the 256MB sticks, it seems to run fine. I've tested with
Win98 and with Linux, and the problem can be reproduced with both
operating systems. It seems to be related to the AGP slot somehow.
I haven't tried modifying the board, to see if the problem is in fact,
one of the known problems for 440BX boards. The 512MB I can use on the
machine, is a good fit for use with Win98. And the machine is quite stable
with the two sticks - it has passed 16 hours of Prime95.
    Paul

 I believe though different mnufacturer should not pose any problem.
So you currently are not running in dual channel mode. If you can get 
another 512mb piece you'll enjoy a slight performance boost as far as memory 
access goes. Adding a single 1gig piece might get you more performance since 
you'll be swapping to the hard drive less often.
It's definately wise to try and match the specs of the new memory to the 
old.

     Paul-
Machine with Gigabyte GA-686BX motherboard  was running with two 128mb
memory strips. They as well as 512mb strip I bought both have same
number of chips, number 16 is made up by counting chips on both sides
of strips.
Gigabyte GA-686BX motherboard issue now is taken out of my hand so I
need not worry anymore.
Thanks Paul for your time.

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I looked at the price aspect.
If I install 3 additional 512mb strips it will cost me about £60 in
total to get 2gb RAM in total, if I want 3gb RAM total cost goes up to
£110. Two 512mb strips cost less than one 1gb strip. That is a bit
strange to me. Situation appears to be similar as in prices of
different capacity of hard drives.

 or Sempron supports 2GB modules. (TheCrucialsite lists max memory as
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