ram help.

i am buying another stick of ram i was wondering if it would be
compatible with the ram i currently have. this is the ram i currently
have http://support.gateway.com/s/PC/R/5876/5876sp3.shtml and i am
wanting to get another one from this list but i cant choose one cause
i have no clue what i need exactly
http://www.newegg.com/Product/Produc...ubCategory=147.

if anyone could suggest one that would be compatible with my memory i
would be very grateful.

wakka wrote:
> i am buying another stick of ram i was wondering if it would be
> compatible with the ram i currently have. this is the ram i currently
> have http://support.gateway.com/s/PC/R/5876/5876sp3.shtml and i am
> wanting to get another one from this list but i cant choose one cause
> i have no clue what i need exactly
> http://www.newegg.com/Product/Produc...ubCategory=147.
>
> if anyone could suggest one that would be compatible with my memory i
> would be very grateful.
>

Crucial says your motherboard has four slots.

http://www.crucial.com/store/listpar...+Center+GT5028

You currently have 2x512MB, which preferably are installed in slots
selected for dual channel operation. With one pair of DIMMs, you
might expect DDR400 operation, with Command Rate 1T (the fastest).

1) If you pull the 2x512MB sticks out, and put 2x1GB as their replacement,
you get to keep the DDR400 operation, with Command Rate 1T operation.

Installed - 2x1GB = 2GB total Fastest

2. If you add a matched pair of 512MB DIMMs, using the two empty slots,
you also get 2GB total, just as in the (1). But the memory speed
will either be DDR400 Command Rate 2T or DDR333 Command Rate 1T. A
command rate of 2T, is about the same magnitude of penalty, as
dropping the memory speed from DDR400 to DDR333. DDR400 2T is slightly
faster, of the two cases.

Installed - 4x512MB = 2GB total 20% slower

3. If you add a matched pair of 1GB DIMMs, using the two empty slots,
you get a total of 3GB. Speed is same as (2). An added penalty, is
the memory controller can no longer interleave at the page level,
as all banks are not identically dimensioned.

Installed - 2x512MB + 2x1GB = 3GB total 20+ % slower

4. If you put three DIMMs total in the computer, that really slows
things down. On the modern Athlon64 processors, they use virtual
single channel operating mode. To add insult to injury, since one
channel will have two DIMMs on it, that channel forces the speed
down, in the same way as (2) or (3). So it is single channel,
with a slower clock or command rate.

Installed - 2x512MB + 1x1GB = 2GB total A lot slower

So that is the range of upgrade strategies for your S939
motherboard with four memory slots. If it was my board, I would
go with two matched 1GB DIMMs, and sell the 2x512MB DIMMs, once
you've proved the new DIMMs work, using tools like memtest86+ and
Prime95 torture test option.

Note - the above rating system ("20% slower") is the raw memory
bandwidth. Divide by 3 to get the application level penalty. In other
words, roughly speaking, 20% less bandwidth would be about 6% slower
application execution. (I made up this rule of thumb, and others
are free to disagree with it.) Photoshop users see more impact
than the average application the above rule of thumb applies to.

If your BIOS has user adjustable memory settings, you can simulate
the performance of most of the above configurations. You can set the
memory to DDR333, for example, to simulate case (2). You can move
the DIMMs around so that both 512MB DIMMs are on the same channel.
That would simulate virtual single channel mode, and with two loads
on the same channel, you would get a representative amount of
bus loading. So you can test the impact of case (2) or case (4)
with the RAM you already own. By doing your own testing first,
that will help you decide whether the impact of a sub optimal
memory configuration is acceptable or not.

HTH,
Paul