A computer is used to store data in memory and we have found that there are such a large variety of storage devices available for storing data in the computer system. the primary reason is that the cost per byte of storage and access time of the memory. and it also depends that whether storage is volatile or not.

Computer Memory Hierarchy and Characteristics

In a computer, the memory system is organized as a hierarchy consisting of a number of levels. at the top of the level, the computer uses cache memory that has high speed, low capacity, and volatile memory. and at the bottom level computer uses the high speed, slow access, and nonvolatile memory to store the data.

Another thing is that the semiconductor memories that use high-speed transistor flip flops also know as cache memories are most expensive and also work in the fast mode. you can see the capacity, access time, and cost per byte for the memories shown below.

Cache Memory

  • Average capacity - 16 MB
  • Technology - High speed integrated circuits
  • 0.5 ns average time to access a byte
  • Instructions and data to be immediately used
  • 10 units cost per byte

Main memory

  • Average capacity - 512 MB
  • Technology - Integrated circuits(DRAM)
  • 5 ns average time to access a byte
  • Used by the programs and data
  • 1 unit cost per byte

Disk memory(Hard Disk)

  • Average capacity - 750 MB
  • Technology - Magnetic surfaces on the hard disk
  • 8 ms average time to access a byte
  • Used for large data files and for program overflow from main memory
  • 1/100 units cost per byte

Flash memory(EEPROM)

  • Average capacity - 32 GB
  • Technology - Integrated circuit
  • 1 us average time to access a byte
  • used to store personal program and data files and backup of data files
  • 1/1000 units cost per byte

LTO-6

  • Average capacity - 6.25 TB
  • Technology - Long 1/2'' tape wound on cartridge
  • Used to store history files and backup for the disk. data program exchange between installations.
  • 1/1000 units cost per byte

CDROM

  • Average capacity - 600MB
  • Technology - Laser disk
  • 500 ms average time to access a byte
  • Used to store video files
  • 1/100000 units cost per byte

Blu-ray disc

  • Average capacity - 50 G
  • Technology - Laser disk
  • 500 ms average time to access a byte
  • Used to store video files
  • 1/10000 units cost per byte

To get the best result while in terms of storage we need to use a combination of all these types of storage devices. cache memory is used to store the data that needs to be accessed immediately. and the random access memory is used to store the programs that currently executing. the files that need in the future stores in the disk. and the magnetic tape storage device is used to store the data that used rarely.