Discussion on memory hierarchy, including registers, cache memory, main memory, USB/flash memory, hard disk, and magnetic tapes. Emphasis on size and access time as major factors, and the concept of hierarchy to balance cost and access time. Registers are small (8/16/32 bit) and associated directly with the CPU. Cache memory is measured in KB/MB, main memory (RAM) in GB. USB/flash memory like pen drives or SSDs are popular for their speed.