• One Memory Word – Each memory location 
  • Word length – no. of bits in each location
  • Word Size – 8bits/16 bits/ 32 bits
  • Memory capacity – total no. of locations in a memory 
  • To compare memory capacity – know word size & no. of location 
  • Unique address – Each memory location is identified
  • No. of bits to specify address depends on capacity of memory 

If n address bits -> address complete range of memory with 2n location / words 

Eg: If 10 address bits – max memory size 1024 location 

1 kilo =1024

Start address 000…00

End address 111…11 

Memory Types

  • Older Days – magnetic core – non-volatile
  • Current Days – semiconductor – volatile

Semiconductor types

  • Static RAM 
    • preserves content of all location as long as power supply
    • uses flip flop   

  • Dynamic RAM 

    • Retains content of any location only for few ms. 

    • Refreshing 

      • With in that period,  each location must be written again with same content

    • uses transistors & capacitors

Random Access & Sequential Access memories

Random Access 

  • Access time is the same for all locations
  • Any location can be accessed without any other relation to other
  • Core & semiconductors are RAM

Sequential Access memories

  • In sequential memory – read & write access are sequential 

  • Read/Write mechanism encounters location physically one by one

  • Time for 1st location – shortest & last is the longest
  • Thus access time varies
  • Eg: magnetic tape

Sequential + Random Access – Floppy & Hard disks

RAM & ROM

  • RAM - Random Access Memory -  volatile
  • ROM – Read Only Memory – non-volatile

Semi-conductor memory used for 2 different applications

  • Read/ Write Memory (RWM)
  • Read Only Memory (ROM)

Technically RWM denotes ROM & RAM. In industry practice – RWM denotes RAM.