[OS]Main memory management

Memory Background

processor registers <-> (word) cache memory <-> main memory <-> (block) auxiliary storage(Disk)

• Block
  • Size: 1 ~ 4KB
• Word
  • Size: 16 ~ 64 bits

Address Binding

• Compile time binding
• Load time binding
• Run time binding

Dynamic Loading

• Save all routines to disk in replaceable form
• Efficient use of memory

Swapping

• Swap-out
• Swap-in

Memory Allocation

• Continuous Memory Allocation
  • Uni-programming
  • Multi-programming
    • Fixed partition (FPM)
    • Variable partition (VPM)
• Non-continuous Memory Allocation

Uni-Programming

• Multiprogramming degree = 1
• Problem
  • Program Size > Memory Size
  • Kernel Protection
  • Low system resource utilization
  • Low system performance
• Soultion
  • Overlay structure.
  • Use boundary register
  • Multi-programmin

Fixed Partition Multiprogramming

• Process : Partition = 1 : 1
• Multiprogramming degree = k
• Fragmentation
  • Internal fragmentation
  • External fragmentation

Variable Partition Multiprogramming

• No internal fragmentation
• External fragmentation issue
  • Coalescing holes
    • Low overhead
  • Storage Compaction
    • High overhead
• Placement strategies
  • First-fit
    • Simple and low overhead
  • Best-fit
  • Worst-fit
  • Next-fit
    • Low overhead

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Reference

Main memory management