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Memory and Storage

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Title: Memory and Storage


1
Memory and Storage
  • - Sheetal
    Gosrani

2
Overview
  • Memory Hierarchy
  • RAM
  • Memory Chip Organization
  • ROM
  • Flash Memory

3
Memory Hierarchy
Increasing performance and increasing cost
  • Slow and inexpensive

4
Memory Hierarchy (contd)?
  • Registers
  • top in the hierarchy
  • matched in speed to the CPU
  • but are large and consume significant power
  • number of registers in a processor are small
  • Secondary and off-line storage devices
  • at the bottom of the hierarchy
  • cost per stored bit small in terms of money and
    power
  • but access time is very long compared to
    registers

5
Random Access Memory(RAM)?
  • The term random means any memory location can
    be accessed in the same amount of time regardless
    of its position in the memory.
  • Volatile memory
  • Types of RAM
  • SRAM
  • DRAM

6
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7
Static RAM
  • Static RAM (SRAM) based on flip flops
  • Contents of each location persist as long as
    power is applied.
  • Fast but relatively large
  • Consume a lot of power
  • Used for memory applications that are small but
    fast

8
Dynamic RAM
  • Dynamic RAM (DRAM) employ capacitors
  • Capacitor stores electric charge whose level
    represents a 1 or 0
  • Capacitors dissipate with time and hence the
    charge must be restored frequently
  • DRAMs
  • smaller, slower than SRAMs
  • support low cost, low power and high density and
    hence used in main memory

9
Memory Chip organization
10
RAM chip
  • A0 Am-1 Address lines from 0 to m-1
  • CS Chip Select (CS 0, chip selected)?
  • WR ReadWrite (WR 0, write operation)?

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12
RAM Grid
13
RAM Grid
  • During read operation
  • Entire row is selected
  • It is fed into the column MUX
  • MUX selects a single bit for output
  • During write operation
  • Single bit to be written is distributed by the
    DEMUX to the target column
  • Row decoder selects the proper column to be
    written

14
Read Only Memory(ROM)?
  • Data stored in these chips is nonvolatile -- it
    is not lost when power is turned off.
  • On turn on, the computer loads BIOS from ROM
  • Data stored in these chips is either unchangeable
    or requires a special operation to change
  • Applications Videogames, calculators, microwave
    oven, etc

15
Read Only Memory(ROM) (contd)?
  • Lets see the circuit for a ROM that stores four
    four-bit words(0101, 1011, 1110, 0000)?
  • PROM burner allows contents of the ROM to be
    overwritten only once
  • EPROMs could be written several times
  • EEPROMs allow the content to be rewritten
    electrically

16
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17
Flash Memory
  • A section of memory cells can be erased in a
    single step, or 'flash', thus the name
  • Nonvolatile memory
  • Flash memory is used for easy and fast
    information storage in such devices as digital
    cameras, mobile, video game consoles

18
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19
References
  • Textbook Computer Organization and Architecture
  • Wiki pages
  • http//en.wikipedia.org/wiki/Computer_storage
  • http//en.wikipedia.org/wiki/Dynamic_random_access
    _memory
  • http//computer.howstuffworks.com/ram.htm
  • http//computer.howstuffworks.com/computer-memory1
    .htm

20
Thank you
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