On Thu, 10 Nov 2011 18:52:41 -0600, Karl Townsend wrote:

I'm trying to run another app on my shop 'puter...

Its an HP D530 P4 with 512 memory. Lots more specs he
http://h18000.www1.hp.com/products/q.../11632_na.html

When it boots it says DDR 266 and runs up to 512 on the memory test. I
pulled the stick and all it says is DDR 266, no other labels.

On New Egg, this is the closest I can find:
http://www.newegg.com/Product/Produc...20266%20pc2700

Will this work? Do different size sticks work together?

From specs, it looks like that memory part will work. (Spec says: "It is
not necessary to add memory in pairs. Memory upgrades are accomplished by
adding single or multiple DIMMs of the same or varied sizes. ... the 865G
chipset supports non-ECC 266MHz (PC2100), 333MHz (PC2700) and 400MHz
(PC3200) DDR memory. For best performance, add in pairs, add in same
channel, and do not mix speeds. For dual-channel performance, DIMMs
must be same size, same DRAM technology, same DRAM bus width, and
either all single-sided or double-sided DIMMs. Brand and timing specs
are not an issue. If speeds are mixed, default will default to the
slowest DIMM.")

In other words, different sizes work together ok, but may run slower
because dual-channel access won't work with different sizes lined up.
(See http://en.wikipedia.org/wiki/Multi-channel_memory_architecture
picture of two yellow and two orange slots, one of each per channel.
You didn't say if you have Minitower D530, which has 2 channels and
4 DIMM slots, or Ultraslim Desktop D530, which has 1 channel and 2
DIMM slots. With only one channel, "dual-channel performance" isn't
possible anyway.) If you are running low-end apps on small data sets
on an obsolete computer, dual-channel performance probably won't matter.

32-bit MS Windows XP maxes out using 3GB even if your computer has
4GB RAM installed. It might not be worth the money to get 4GB but
http://www.ebay.com/itm/2GB-DDR-SDRAM-PC3200-2-GB-PC-3200-DDR400-2X-1GB-Memory-/130468032164?pt=LH_DefaultDomain_0&hash=item1e6080 2ea4
for $22.35 or
http://www.newegg.com/Product/Product.aspx?Item=N82E16820161161 or
http://www.newegg.com/Product/Product.aspx?Item=N82E16820146366
for about $45 would get you up to 2GB (or 2.5GB if you have 4 slots),
which helps XP run faster and more reliably.

SDRAM comes in 168-Pin single data rate, 184-Pin DDR, 240-Pin DDR2,
and 240-Pin DDR3. For a comparison of DDR with DDR2 and DDR3 parts see
http://en.wikipedia.org/wiki/Fileesktop_DDR_Memory_Comparison.svg
from http://en.wikipedia.org/wiki/DDR2_SDRAM. Per picture, the DDR
notch is at about 73mm from one end of stick, if you want to double-check
what you have.

--
jiw