I recently purchased some new memory; will it work with my old RAM?
Short answer: In most cases, YES.
Long answer: There are several factors in determining whether your old memory will be compatible with new memory. These are the things you will need to check:
Do you have empty slots?
Do you need to install in pairs?
Do you have ECC/ECR memory?
Is your new memory the same speed, type, size?
In most cases you can mix memory speeds and sizes; so you can put a 512mb pc2700 with your old 256mb pc2100. In the case of mixed speeds the faster stick will clock down to the slower speed, so the pc2700 will run as pc2100.
If you have purchased ECC/ECR memory you will need to check that your old memory is also ECC/ECR otherwise it will not work. You cannot mix ECC/ECR and non-ECC/ECR, you can, however mix ECR and ECC, though the registered function of the ECR will be disabled.
Something else to remember- your slot max is your total max divided by the number of slots. So your total max is 2GB and you have 4 slots, you can ONLY purchase, at most, 512MB RAM, otherwise it will not read.