I know on a hard drive you can have bad clusters, but in RAM, can you have bad pages? And what's the main reason RAM goes bad? thanks.
I think when RAM goes bad, all of it is bad, rather then part of it. To be honest though, I have no idea ! One of the biggest causes of RAM failure is static electricity. RAM (just like the rest of your hardware) is very sensitive, and if you're not properly grounded, you are twice as likely to kill it!
Hard drives are more robust than RAM when it comes to damaged sectors. In HDs, if a sector is damages, it is marked bad and the FS doesn't use it to store data. In RAM however, it can cause all sorts of problems. I know of experience, and sometime its hard to reproduce or diagnose. Usually if the RAM is damaged, you'll experience crashes, system instability and random errors.