This document defines and describes different types of computer memory. It explains that computer memory can be either primary/main memory, which is volatile and allows direct CPU access, or secondary memory, which is non-volatile storage like hard disks. The document details different types of primary memory including RAM and ROM. It also covers various forms of secondary memory such as hard disks, CDs, DVDs, USB drives, and Blu-ray discs. Memory is measured in bits, bytes, kilobytes, megabytes, gigabytes, and terabytes.