What type of memory is needed?
 

I have found the following for:

hardware profiler:

sudo lshw

and

BIOS & MOBO profiler:

sudo dmidecode

But they do not show the vernacular in use when one orders memory, e.g.
"PC 3200 DDR400" or "PC5400 DDR2 667MHz"

in my computer, sudo dmidecode yields:

Memory Device
Array Handle: 0x001B
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 1024 MB
Form Factor: DIMM
Set: None
Locator: A2
Bank Locator: Bank4/5
Type: Unknown
Type Detail: None
Speed: 800 MHz (1.2 ns)
Manufacturer:
Serial Number:
Asset Tag:
Part Number:

If I understand the above, this would translate into "DDR800", yes?

But how does one determine the "PCabcd" part of the description and whether DDR or DDR2? Thanks.

If you know which mother board your computer uses, you can go to the mobo manufacturer's web site and download the manual for it and it will tell you exactly which type/types, and configurations you can use for different types if it can handle more than one type.
Sometimes you can find out which mobo you have through the computer manufacturer's web site. I use a utility called Everest ultimate edition to get all hardware information on computers I repair form within Windows. There are many utilities available that will tell you this information, but they are mostly ported to Windows. You can also open the case and look at it, it may be written right on it, usually between the PCI slots.

I don't know how to interpret the output of dmidecode, but if you have a dual channel capable mobo, you would put 400MHz memory in each channel to get 800MHz, which is capable of feeding an 800MHz FSB on a processor. Your best bet is to go straight to the manufacturer for precise answers.
One thing I did notice is this:
Most mobos require you to use the first in line banks, dmicode may not be interpreting the information correctly.

Or you could get a screwdriver, open the case and see what the little sticker on the ram says.

http://www.crucial.com/
http://www.crucial.com/systemscanner/index.aspx

Steve, thanks for the suggestion. Opening the case is easy. Getting the case out to open it is another thing entirely.

teckk, the d/l is an .exe file. Will this run in Linux?

I would recommend you look up your motherboard and see what it supports.

However, you can find more information by running 'dmidecode' as root.

TexMex,

I have the original manual that came with the mobo and have downloaded the pdf. Neither specify the RAM except that it is DDR2 and will support 1066/800/667 MHz memory modules.

The demidecode output is shown in the first post in this thread.

the PCabcd part is just another way of naming the memory speed.
If dmidecode says it's 800Mhz (DDR), then this means they are talking about PC6400 memory (6400MB/s throughput).

Here you have a summary:

Starting PC-3500, it is assumed that it's DDR2 memory.

Ok then, then the board supports DDR2 RAM running at 1066, 800, or 667 MHz. From the dmidecode output, which you should look more closely at, you only posted a small part that doesn't include much useful info, you are currently using a DDR2 800 MHz. So if you want to stay with this speed simply buy another of this type. The marketing name for these is:

PC2-6400 = 800 MHz data & strobe / 400 MHz clock for address and control

see the wiki:
http://en.wikipedia.org/wiki/DIMM