I need to interface some sort of RAM with an ARM processor for my embedded project. Around 128 MB to be exact. I found a computer RAM which claims to be DDR and 1 GB. As I only need 128 MB of RAM for my project, can I just get those individual chips from the RAM and use it in my project? Or is some sort of external circuitry a must? I want to access it through the address and the data bus.
The individual chips are 128M × 4 bits, so the number of chips you need would depend on how wide you want your data bus to be. For example, if you want an 8-bit data bus, you'd need 2 chips.
If you want a full 32-bit data bus, you'll need 8 chips — half the chips on the module — so you might as well just get a module socket and plug the whole thing in.
You can get SDRAM chips that are up to 16 bits wide; you'd only need two of those to fill up the width of a 32-bit bus.