memory and storage
DESCRIPTION
- Sheetal Gosrani. Memory and Storage. Overview. Memory Hierarchy RAM Memory Chip Organization ROM Flash Memory. Memory Hierarchy. Increasing performance and increasing cost. Slow and inexpensive. Registers top in the hierarchy - PowerPoint PPT PresentationTRANSCRIPT
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Memory and Storage
- Sheetal Gosrani
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Overview
Memory Hierarchy
RAM
Memory Chip Organization
ROM
Flash Memory
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Memory Hierarchy
Slow and inexpensive
Increasing performance and
increasing cost
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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
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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
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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
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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
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Memory Chip organization
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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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RAM Grid
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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
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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
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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
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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
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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
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Thank you