Overview

• RAM (Random Access Memory)
  • Dynamic RAM (DRAM): based on capacitors
  • Static RAM (SRAM): based on transistors
• ROM (Read-Only Memory)
  • Programmable ROM (PROM)
  • Erasable Programmable ROM (EPROM)
  • Electronically Erasable Programmable ROM (EEPROM)

Memory Cell

• Select: select cell for read / write operations
• Control: to write or to read
• Data: the bit

Implementation

RAM

Dynamic RAM (DRAM)

• Based on capacitors
• Data stored as the charge of capacitors (high level - 1, low level - 0)
• Requires periodic charge refreshing to maintain data storage

Static RAM (SRAM)

• Based on transistors
• Binary bit stored using transistors (as switches) and voltage
• No need to refresh, holds data as long as power is supplied

Comparison

• DRAM: simpler, smaller, denser, less expensive; requires refresh circuitry
• SRAM: faster, more expensive, less dense