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ECS154A-L28

2 min read

📗 -> 03/18/25: ECS154A-L28

❗ Unit and Larger Context

Small summary

✒️ -> Scratch Notes

Key Characteristics of a memory system

  • Location:
    • CPU: Registers, cache, etc.
    • Internal: Main mem.
    • External: Disks, tapes, etc.
  • Capacity:
    • Word size (WS):
      • Bytes are a fixed 8 bits
      • Word size however varies from machine to machine. Usually the size of an internal register.
  • Unit of transfer:
    - Number of bytes transferred to/from memory per cycle
    - Related to addressable unit
    • Word
    • Sub-word
    • Block (cache line ex)
      • Line size worth of data
  • Access methods:
    • Sequential
      • Scan through memory until you hit target.
      • Data laid out sequentially
      • Tape drives!
        • Slow but very dense, make great backups
      • CD more like this
    • Direct
      • Go directly to area, then sequential
      • What a regular disk drive does
    • Random
      • Go directly to the place that you want.
      • RANDOM access memory (RAM)
    • Associative
      • Access based on contents
      • Content Addressable Memories (CAM)
      • Associative Caches, TLBs, etc.
  • Performance:
    • Access time: time to do a read or write
    • Cycle time: time between operations
    • Transfer rate: rate at which data can be transferred in/out of memory. Bandwidth ex.
  • Physical Type
    • Need 2 (or more) distinct states
    • Semiconductor memory (flip flops / capacitors / etc.)
      • Flash (floating gate)
    • Magnetic surface (tape drives)
    • Optical (optical CDs)
      • Magneto-optical storage?
  • Physical Chars
    • Volatile (flip flops / capacitors)
    • Non-volatile (Most of the above) - Maintaining memory without power

8x4 Memory Chip:

Transclude of ECS154A-L28-2025-03-18-22.13.32.excalidraw

  • 32x8 is shown on the left. We are combining 32x4s to make a 32x8
  • Building a 64x8 memory on th

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