There are three commonly used computer memories:
184-pin DDR-SDRAM operates at speeds from 200 to 400 Mhz used in older personal computers.
240-pin DDR2-SDRAM operates at speeds from 400 to 800 Mhz most commonly used memory these days.
240-pin DDR3-SDRAM operates at speeds from 1066 to 1333 Mhz which is the latest technology that will replace the DDR2 memory.
Modern type of memory being used is DDR. It's subdivided into 3-tiers which are DDR, DDR2, and DDR3. DDR being the slowest and DDR3 the fastest. Chances a new computer will have DDR3, the main important factor is picking a computer that hold a high maximum amount RAM onboard.
different type computer memory is temporary storage memories like RAM, ROM, CPU cache and permanent storage memories like Hard Drive, Pen drive, Optical storage(CD), floppy, tape drive etc
