Memory Hierarchy

memory hierarchy

Memory Hierarchy is a modification used in computer system design to better organise memory and reduce access times.

The following diagram exemplifies many memory hierarchy types:

  1. CPU Registers
  2. Cache Memory
  3. Main Memory
  4. Magnetic Disk
  5. Magnetic Tapes/Tape Drives

1) Registers

  • Directly Communicate with CPU
  • It is a static RAM in computer processor
  • CISC have many register for accepting main memory
  • RISC have more registers
  • Assigned a memory address or instruction or any data

2) Cache Memory

  • Static RAM
  • It may be an IC Separated into levels
  • Holds chunk of data which are frequently used from main memory

3) Main Memory

  • Dynamic RAM/ROM
  • Fast & Large
  • Store data throughout the operation
  • Stores programs & data when they are processed
  • Nothing permanently kept here
  • Every program we execute & every file we access must be copied from storage into main memory.
  • Mainly read/write is done
  • Provide Multiprocessing environment

4) Magnetic Disks

  • Write/Rewrite/Access data
  • Entire disk is divided into platters, each consists of circles called tracks.
  • Each track divided into sectors(ie smallest division in disk)

5) Magnetic Tape

  • Magnetic tape refers to a normal magnetic recording designed with a slender magnetizable overlay that covers an extended, thin strip of plastic film.
  • It is used mainly to back up huge chunks of data. When a computer needs to access a strip, it will first mount it to access the information.
  • Once the information is allowed, it will then be unmounted.
  • The actual access time of a computer memory would be slower within a magnetic strip, and it will take a few minutes for us to access a strip.

Auxillary Memory

  • It is non volatile
  • Lowest cost, highest capacity & slowest access storage
  • Program & Data kept for long time
  • Example Magnetic Tapes & Disks, Papertapes
  • Has Data Stability
  • Work like ROM

Associative Memory

  • Data cannot be identified by address or memory location
  • Also called Content Addressable Memory(CAM) ie. its data is only identified by the content of data itself.

Virtual Memory

  • Uses hardware or software to allow a computer to compensate for physical memory storage by temporarily transferring data from RAM to Disk.
  • Used when computer memory(RAM) run out of storage. It uses a section of hard drive.
  • It is managed by memory management unit(MMU)

Memory Management Hardware

  • Resides in hardware, in operating system & program & applies
  • Involves RAM, memory caches, Flash based SSD
  • Involves allocation of specific memory blocks to individual program as user demands change


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