Need some advice on RAM upgrade please.

[Apollo]

OK so I've finally realised that my 1.7GHz Celeron running WinXP is labouring with 128MB RAM ( actually I realised as soon as I bought the PC ). so it's time to upgrade.
I'm going to buy 512MB RAM but I'm confused.
I have 128MB PC2100 DDR SDRAM but when I go on line to buy new RAM there is also a MHz rating, seems to go from 100MHz up to 400MHz. How do I know what to buy. What does the MHz rating mean?
Sorry to be such a noob but hey some of us just love arcade machines we're not all PC literate, lol.

[Goz]

Here's a breakdown of RAM and frequency

DDR Memory Clock Speeds/Ratings:

Double Data Rate (DDR) memory transfers data at double the rate of your FSB. The PCxxxx rating tells you the maximum megabytes per second that the memory can transfer at the given frequency (FSB). Where xxxx = MB/s. For example PC2100 memory has a bandwidth of 2100MB/s (2.1 GB/s). When talking about FSB I will refer to the actual frequency; not the DDR FSB, which is also referred to as the

[GGKoul]

Another thing, your Motherboard can only accept one type of ram.  I mean, the 133/100mhz ram has different notches on the bottom of it then a PC3200+  stick of ram.  

So you have to purchase a 133mhz ram for your motherboard.  As you cannot purchase higher mhz ram for motherboard, since your motherboard probably won't accept it.

[_Iz-]

Another thing, your Motherboard can only accept one type of ram.  I mean, the 133/100mhz ram has different notches on the bottom of it then a PC3200+  stick of ram.  

So you have to purchase a 133mhz ram for your motherboard.  As you cannot purchase higher mhz ram for motherboard, since your motherboard probably won't accept it.

Not true. The notches are only different between sdram and ddr ram.

You can buy pc3200 and it will run in a board that only needs pc2100.

[GGKoul]

Not true. The notches are only different between sdram and ddr ram.
You can buy pc3200 and it will run in a board that only needs pc2100.

Really??  I was unaware of that.  

[pointdablame]

_Iz- is correct.  You can run any type of DDR in a DDR motherboard.  It won't necessarily run at the rated speed, however.  If you were to put in a 512mb stick of 3200 plus the 128mb stick of 2100 you already have, that 3200 would run at 2100 speeds.  It may also, depending on mobo and ram, cause some troubles.

Chances are it will work just fine, but it may be worth it to stick with one speed and one speed only.

Older SDRAM only ran at either 100mhz or 133mhz I believe, and they are the sticks that will have different notches.  DDR SDRAM motherboards will physically accept any DDR sticks, regardless of speed.

[Apollo]

Cool thanks all, very helpful.

[greywolf22]

Hey Apollo,

One thing you can do is go to www.crucial.com

put in your motherboard manufacturer and model and it will give you a list of memory that will run in your system (granted it's crucial memory, but if your not interested in buying your memory from them its a quick way to see what speeds and type of memory will run on your board)