What is Memory in Information Technology (IT)

What is Memory in Information Technology (IT)

Memory :

Main memory consists of a number of storage locations, each of which is identified by a unique address.The ability of the CPU to identify each location is known as its addressability. Each location stores a word i.e. the number of bits that can be processed by the CPU in a single operation.  Word length may be typically 16, 24, 32 or as many as 64 bits. A large word length improves system performance, though may be less efficient on occasions when the full word length is not used.

Unit                        Description                              Approximate Size

1 bit                    1 binary digit

1 nibble                   4 bits

1 byte                     8 bits                                              1 character

1 kilobyte            1,024 bytes                            »1/2 page, double spaced

1 megabyte       1,048,576 bytes                               »500,000 pages

                           1 million bytes

1 gigabyte       1,073,741,824 bytes                          »5 million pages

                           1 billion bytes

1 terabyte          1 trillion bytes                                 »5 billion pages

Types of Ram

  1. Dynamic Random Access Memory (DRAM)
  • Contents are constantly refreshed 1000 times per second
  • Access time 60 – 70 nanoseconds

Note: a nanosecond is one billionth of a second!

**must be constantly refreshed by the CPU or it will loose its contents

  1. Synchronous Dynamic Random Access Memory (SDRAM)
  • Quicker than DRAM
  • Access time less than 60 nanoseconds
  1. Direct Rambus Dynamic Random Access Memory (DRDRAM)
  • New type of RAM architecture
  • Access time 20 times faster than DRAM
  • More expensive
  1. Static Random Access Memory (SRAM)
  • Doesn’t need refreshing
  • Retains contents as long as power applied to the chip
  • Access time around 10 nanoseconds
  • Used for cache memory
  • Also for date and time settings as powered by small battery
  1. Cache Memory
  • Small amount of memory typically 256 or 512 kilobytes
  • Temporary store for often used instructions
  • Level 1 cache is built within the CPU (internal)
  • Level 2 cache may be on chip or nearby (external)
  • Faster for CPU to access than main memory

 

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