Memory Unit

Used to represent the data size. A bit is the smallest unit size. The data is stored in binary value of 0 or 1. Computer memory is stored into smaller parts called as cells which has unique address in between 0 and it's size - 1.
bit 0 or 1
1 nibble 4 bits
1 byte 8 bits
1 kilobyte 1024 bytes
1 megabyte 1024 kb
1 gigabyte 1024 mb
1 terabyte 1024 gb
1 petabyte 1024 tb
1 exabyte 1024 pb
1 zettabyte 1024 eb
1 yottabyte 1024 zb

Types of memory

Based on location, it is of 4 types.
  1. Register memory
  2. Cache memory
  3. Primary memory
    1. RAM - Volatile
      1. DRAM - dynamic
      2. SRAM - static
    2. ROM - Nonvolatile
      1. PROM
      2. EPROM
      3. EEPROM
  4. Secondary memory
    1. Fixed storage
      1. HDD - Hard Disk Drive
      2. SSD - Solid State Disk
      3. Internal flash memory
    2. Removable storage
      1. Optical disks
      2. Memory cards
      3. Pendrives
      4. Floppy disks
      5. Magnetic tapes

1. Register memory

  • Smallest and fastest memory in computer.
  • It is in the form of registers reside inside CPU.
  • Temporarily stores the data for faster access by CPU.

2. Cache memory

  • Small and faster than primary memory.
  • It stores the frequently used data or instructions by CPU.

3. Primary memory

  • It is the part of the computer unlike secondary memory.

3.A. RAM (Random Access Memory)

  • It is volatile memory means that it stores data or instructions temporarily.
  • It loses all data when we shut down the computer.
  • It system's RAM is more, it works faster.

3.A.I. DRAM (Dynamic RAM)

  • It refreshes it's memory constantly.

3.A.II. SRAM (Static RAM)

  • It doesn't need to refresh so much constantly unlike DRAM.
  • As it acts like system cache it works faster than DRAM.

3.B. ROM (Read Only Memory)

  • It is nonvolatile memory means that it stores data or instructions permanently.
  • It doesn't loose data when we shut down and helps in getting instructions for booting process.

3.B.I. PROM (Programmable ROM)

  • Once program is written in PROM, it remains there forever.

3.B.II. EPROM (Erasable Programmable ROM)

  • Until the memory is exposed to ultraviolet light, the content will be there forever.

3.B.III. EEPROM (Electrically Erasable Programmable ROM)

  • Until the memory is exposed to electric charge, the content will be there forever.

4. Secondary memory

  • It is connected to the computer externally to add additional functionality.