How to know what RAM type and correct amount to buy to upgrade PC.

i usually go to Kingston.com or crucial.com and you just put in the manufactuer and model of your pc and it will tell you what you  need.

Look inside your motherboard manual. You can find it online if you dont have it.  It will tell you the MAX amount and MAX speed of what type of ram you need.  

if this is a prebuilt pc like a dell or hp etc. those two sites also tell you the max your system can take.

If you are in doubt as to what motherboard or type of ram that is inside your coputer, try this simple program called CPUz which can give you all that info.
http://www.softpedia.com/progDownload/CPU-Z-Download-6980.html

This is my RAM type:

512 MB
DDR PC2100
 EMPTY
 EMPTY
 EMPTY

Maximum Memory Capacity:  1048576 MB
Currently Installed Memory:  512 MB
Available Memory Slots:  3
Number of Banks:  4
Dual Channel Support:   N.A.
CPU Manufacturer:  AuthenticAMD
CPU Family:  AMD Athlon(tm) XP 1800+ Model 6, Stepping 2
CPU Speed:  1533 MHz
 

I want to order another 2GB, probably one stick.  Do I need to order the PC2100 type or does it matter (i.e. can I just order the DDR type and not worry about the number (PC2100))?

Where is the best and cheapest place to order?

Can anyone please assist with this question so I can then close.

Thanks.

Can you identify the motherboard model as that would make it infinitely easier to give you direction.
The mainboard tab in CPUz will give this info.

But without referring to the motherboard do I have to the specific PC2100 RAM or will any DDR RAM do?

It depends on the motherboard as it will determine what is compatible. You might be able to mix and match the PC 2100 with faster ram like PC2700 , PC3200 and they will clock down to the PC2100 speed, BUT that depends on the motherboard. Some will and some won't. We can't tell you for sure without the model of the motherboard.

Where is the cheapest place to buy RAM?

Hello can someone please answer this before I close this?

Thanks