Memory Hierarchy

• Registers

—   In CPU

• Internal or Main memory

—   May include one or more levels of cache

—   “RAM”

• External memory

—   Backing store

Memory Hierarchy - Diagram

Performance

• Access time

—   Time between presenting the address and getting the valid data

• Memory Cycle time

—   Time may be required for the memory to “recover” before next access

—   Cycle time is access + recovery

• Transfer Rate

—   Rate at which data can be moved

Physical Types

• Semiconductor

—   RAM

• Magnetic

—   Disk & Tape

• Optical

—   CD & DVD

• Others

—   Bubble

—   Hologram

Physical Characteristics

• Decay


• Volatility


• Erasable


• Power consumption

Organisation

• Physical arrangement of bits into words


• Not always obvious


• e.g. interleaved