the dangers in buying RAM without knowing the details

Recently I decided to upgrade my computer’s RAM. I have a Dell Inspiron 600m. I decided to be cheap (a bad idea), and look on ebay. I found a couple sellers with RAM guaranteed to work on my laptop, so I picked the cheapest one: 2 1/2gig modules for under $80. Wow! I thought I got a deal, since Dell’s website lists the same price for only 1 module.

Anyways, I installed it with no problems at all. But within a month, my Windows started to crash over & over again. I had been downloading various new software, so I thought that one of those may be the culprit (especially since a couple blue screens mentioned similar stuff), but then when the blue screens continued even after uninstalling random programs,
I began to think the new RAM was the problem. I didn’t do anything about it (I didn’t want to go back to half the amount of memory), and windows continued to suffer. (see previous post on this)

Now, though, it is time to delve deeper into this issue.

I see I used to have 2 256mb DDR RAM with 333MHz, or PC2700. (by Promos Technologies)
The new RAM is 2 512mb DDR RAM with 266MHz, or PC2100, by Samsung. (interestingly, this RAM, plus its ebay posting, did not show the frequency in MHz. I calculated that now (divide it by 8x) to get that number)
You see the difference? The main issue is the frequency, which dictates the bus speed, or how FAST the RAM can transfer data to the processor. (got this definition from a kid’s site online!)
On further research online, I found out how important it is to know all the details. Here I found more information on what to look out for when upgrading RAM, and here is some excellent detailed info on RAM frequency & latency.

I still do not know how downgrading my frequency while upgrading the amount of RAM memory really affected my computer, or if it was a very bad mistake or not, but I’m still using the new RAM, and so far I’ve been fine with my new Linux & Windows(restored) partitions.