I just removed my xubuntu 11.10 32 bit, and installed xubuntu 11.10 64 bit. So far I've found it's fantastic, and now want to increase my RAM from 2GB to 4GB.
If someone could help me find out what chips I need, and also if I would need to install something when I change it.
More info below:

sudo dmidecode --type 17

# dmidecode 2.9
SMBIOS 2.5 present.

Handle 0x000F, DMI type 17, 27 bytes
Memory Device
Array Handle: 0x000E
Error Information Handle: No Error
Total Width: 64 bits
Data Width: 64 bits
Size: 2048 MB
Form Factor: SODIMM
Set: 1
Locator: M1
Bank Locator: Bank 0
Type: DDR2
Type Detail: Synchronous
Speed: 667 MHz (1.5 ns)
Manufacturer: Mfg 0
Serial Number: 1234-B0
Asset Tag: Not Specified
Part Number: SODIMM000

Handle 0x0010, DMI type 17, 27 bytes
Memory Device
Array Handle: 0x000E
Error Information Handle: No Error
Total Width: Unknown
Data Width: Unknown
Size: No Module Installed
Form Factor: SODIMM
Set: 1
Locator: M2
Bank Locator: Bank 1
Type: DDR2
Type Detail: Synchronous
Speed: 667 MHz (1.5 ns)
Manufacturer: Mfg 1
Serial Number: 1234-B1
Asset Tag: Not Specified
Part Number: SODIMM001

I believe the "SODIMM" indicates this is the laptop form factor for DDR2 667 as opposed to the desktop form factor.

I'm not sure what other constraints there might be.

I just did a search at newegg for SO-DIMM DDR2 667 and that seems to narrow down everything but size and brand. So I'm moderately confident there isn't another detail of type information needed.

Your laptop apparently has an empty socket for a second SO-DIMM. That doesn't 100% guarantee that it really supports 4GB or that an unmatched pair of SO-DIMMs will play together well. But my best guess is adding a second 2GB SO-DIMM DDR2 667 should work.

Note some of those say "200-pin" and others don't. That isn't a difference, all SO-DIMM DDR2 is 200-pin. Some of those say "unbuffered" and others don't say. I'm pretty sure not saying that is the same as saying "unbuffered". If it were "buffered" or "registered" it would always say that, and I'm nearly sure unbuffered (or not saying whether it is buffered) is what you want.

You mean install software to enable the added ram?? No, the BIOS should recognize the change in ram size on reboot (might ask you to confirm that in BIOS setup on that first reboot). Linux will recognize the new ram once the BIOS does.

Do NOT trust DMIdecode outputs to get I.D. exactly what RAM type you are running.

The easier way to know for sure what RAM you are running is to check the installed RAM and slots. Remove and check an installed and running RAM stick for the type (they almost always have a sticker on the side of the stick with the RAM specs). If you want to upgrade you RAM, you'll have to find the RAM slots anyway. (Unless its a laptop with 2 different sets of RAM slots that does happen).

Its best to do that, not only so you get the right RAM, but also so you dont go buying RAM sticks for a system that always has all its RAM slots filled.

You can also check by getting some model number (easy with the motherboard model number, harder but possible with the full 'system' model number that manufacturers like dell use).

@ johnsfine- SODIMM is 'small outline dual in-line memory module'. Its typically used in all laptops (so is some ways it is 'laptop RAM') but there are quite a few newer SFF systems using SODIMM, some printers and routers. Besides speed ('DDR2-677', 'DDR3-1066' etc) there is also CAS (latency), voltage, and size.

Most SODIMM DDR2 should be using the same size. There might be rare examples that only take 1/2 hieght DDR2 SODIMMs. Voltage, its almost all 1.8v, and even if someone installed 1.8v rated DDR2 SODIMM in the system with 1.6-1.7v sticks it _should_ run OK (but the system will use more power, and could be more unstable). CAS will vary a lot (the RAM will run at the CAS rating of the 'slowest' (in CAS and MHz) RAM).

BTW, 'buffered', 'registered' (etc) RAM is normally only found on severs. But just to make life complicated, yes, there is buffered etc. SODIMMs.

I have checked RAM sticks in a lot of computers when trying to figure out what upgrades might be compatible and almost never found useful information on that sticker. I have gotten much better info from DMIdecode.

In hindsight I think you're right. While I have mostly seen correct info from DMIdecode, the most common incorrect info I have seen is empty slots. The slots DMIdecode reports as filled, pretty reliably exist and contain what it says they contain. But the slots it reports as empty sometimes don't exist at all.

I knew all that. I was answering the question from the point of view of purchasing the ram sticks. At typical online vendors you will see this form factor described as "laptop DDR2" rather than described as "SODIMM DDR2".

Best thing to do is look at the manual and hopefully it will have a listing of compatible RAM sticks. If not, go to the store with the laptop and have them test RAM sticks on it. I had to do this with my netbook because many RAM sticks didn't work, it wouldn't boot. They were all the right frequency and DDR3, but they didn't work.

EDIT: Oh, and for my laptop I ordered RAM online ... bad idea. Although I can use one of the new RAM sticks, I can't use both at the same time. It's very strange. I have to keep one of the ancient $ony RAM sticks (the only good one) in there or it won't boot. I don't understand why, but I have tried all possible combinations, and the rule seems to be it must have a $ony RAM stick in there.

I completely agree. For my netbook, it lists the RAM as DDR2 at a low frequency (677 or 800), when in fact the RAM is DDR3 and high frequency (10600 or 13000). Don't trust it, take the RAM stick out and look at the label. However, I still recommend ether the manual or the store as I said above.