Memory

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Memory

• Farhana Rahman
• December 7th , 2004
• CS147, SECTION 3

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Outline

• Memory Hierarchy
• Addressing Modes
• Architecture
• Types of Memory

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Memory Hierarchy

• Memory refers to any storage medium used for
  storing information. Since there are many
  different kinds of storage media , we can
  categorize them according to the memory speed.The
  memory hierarchy is as follows
• Cache Memory
• Secondary memory
• Main (primary) memory
• Archival memory

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Memory Characteristics
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Definition

• Cache Memory The cache memory is a small section
  of memory that is usually placed between the
  processor and the main memory and is used when
  the main memory speed is much slower than the
  processor speed.
• Main (Primary) Memory The main memory contains
  the primary storage space, which is randomly
  accessible by the processor.The primary function
  of the main memory is to store the instructions
  and data necessary for the current execution of
  the processor.

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Definition

• Secondary Memory The information stored in the
  main memory is not easily accessible to the
  programmer and is not suited for storing a lot of
  information. Secondary storage media are useful
  for this purpose.
• Archival Memory Archival memory refers to
  permanent storage media.This include media such
  as cards and paper printouts. Their use is
  strictly for the programmer to store computation
  results.

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Addressing Modes

• In order to access the memory, an address must
  be provided.The manner in which the address is
  specified in an instruction is called the
  addressing mode. Addressing modes can be
  categorized into
• Basic addressing modes
• Special addressing modes

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Basic Addressing Modes

• Most computer systems use a number of basic
  addressing modes to obtain operands from memory
  many high performance processors include
  additional addressing modes consistent with the
  design philosophies of the processor. Basic
  addressing modes include
• Implied addressing
• Immediate addressing
• Register Addressing
• Direct Addressing
• Register indirect addressing
• Implied register indirect addressing
• Indexed addressing

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Basic Addressing Modes
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Basic Addressing Modes
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Basic Addressing Modes
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Special Addressing Modes

• Many processors have additional or special
  addressing modes that facilitate ease
  implementing language constructs and primitives
  often used in operating systems and other systems
  programming environments. Special addressing
  modes include
• Relative addressing
• Base addressing
• Page addressing
• Indirect addressing

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Special Addressing Modes
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Special Addressing Modes
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Virtual Memory
In some computer systems it is convenient for the
user to be able to specify a memory space that is
larger than the actual installed memory space.
This is called virtual memory.The operation of a
virtual memory system uses the concept of memory
segmentation. The users entire virtual memory
space is segmented into pages of segments and is
stored as pages or segments in secondary memory.
A page is a fixed block of memory, whereas a
segment is a variable-size block of memory.
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Memory System Architecture

• The main elements of the memory system
  architecture are
• Memory Cells
• Memory Organization
• Bit-Slice Organization
• Memory Segmentation
• Board/Bank Segmentation
• Memory Access Time

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Memory Cells

• The memory cell is a simple flip-flop or a
  bistable multivibrator that can be found in one
  of two stable states an ON state and an OFF
  state.
• Memory components are composed of three major
  parts the memory cells, the row decoder, and the
  column decoder.

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Memory Organization

• Memory organization is usually given in terms of
  the number of individually accessible or
  addressable words in the chip and the word
  length.
• Bit Slice Organization The concept of
  bit-slice organization is to have many chips
  operating together in parallel, each responsible
  for the operations within a thin slice (a few
  bits) of the word.

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Memory Organization

• Memory Segmentation Although the bit-slice
  organization technique provides the necessary
  tools for the design of a memory system with any
  width, the memory segmentation technique gives
  the necessary tools for the design of a memory
  system with any depth. In memory segmentation,
  many memory chips are connected together to form
  the complete memory system.

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Memory Organization

• Board/Bank Segmentation Often only a fixed
  number of memory chips can fit into a specific
  size of circuit board. If more memory is
  required, multiple memory boards are used. The
  portion Of memory located on a particular board
  is called a memory bank. The total memory is
  composed of many memory banks. All banks are
  usually connected to a motherboard.

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Memory Access Time

• Memory Access Time This is an important
  performance parameter for memory chips.
• Maximum Access Time This is the delay time the
  chip requires to search through the memory cells
  for the addressed word. The output can be read
  after this time. A slightly longer time is
  sometimes required to write data into memory.

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Memory Types

• Memory components are extremely useful for many
  purposes in addition to storage. There are two
  basic types of memory
• Read-only memory (ROM)
• Read/write memory (RAM)
• Read-Only Memory (ROM)
• It is read only it can be read from but not
  written to.
• It is not volatile Its contents are not lost
  when power is off.

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Read-Only Memory

• Applications of ROM There are many applications
  of ROMs, some of which include
• Permanent information storage
• Code conversion
• Multiple output function generation

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Read-Only Memory

• Types of Rom
• ROM
• PROM (Programmable read-only memory) An
  example of a PROM is the P2764A production EPROM
  chip.
• EPROM (Erasable programmable read-only memory)
  More versatile and popular type of ROM .EPROMs
  are ideal for experimentation and development
  when the final edition of the program is not yet
  available.
• EEPROM (Electrically erasable programmable
  read-only memory) Information can be directly
  and dynamically erased electrically under program
  control.

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Read/Write Memory
These are volatile memories, because they store
information only as long as power is applied. The
primary use of RAMs is temporary data storage ,
often called scratchpad memory, because the RAM
can be written into and later read by the user.
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RAM Types

• Static Memory For static memory, the memory
  cells are simple flip-flops or bistable
  multivibrator with two stable states so that the
  cells can hold their state permanently as long as
  the power is applied.
• Dynamic Memory (DRAM) DRAM chips have much
  simpler memory cells in which the state of the
  memory cell is indicated by the presence or
  absence of stored charge in a capacitor.As time
  passes, charge leakage occurs and the information
  is lost even if power is left on.
• Pseudo-static Memory These chips are actually
  dynamic memory. They act like static memory
  because the refresh circuitry is provided inside
  the chip.

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References

• John Y.Cheung, and Jon G.Bedeson , Modern
  Digital Systems Design. New York West
  Publishing Company, 1990.
• Anthony J. Dos Reis , Assembly Language And
  Computer Architecture Using C and Java. United
  States Thomson Course Technology, 2004.