Rahman

Memory

Farhana Rahman

December 7th , 2004

CS147, SECTION 3

Outline

Memory Hierarchy

Addressing Modes

Architecture

Types of Memory

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

Memory Characteristics

Memory Type

Cache Main Secondary Archival

Technology TTL MOS Magnetic Paper

Speed

(access time)

10^1 ns 10^2 ns 10^3 ns 10^5 ns

Size

(capacity)

Small,< 8K Medium,

64K-8M

Large,

300K-1G

Very large,

Usage Processor,

Data Buffer

On-line, Dynamic,

Temporary Storage

On-line,

Bulk storage

Archival, Off-line,

permanent storage

Representative

Example

TTL

memories

Semiconductor

Memories

Floppy disk,

Hard disk,tape

Paper

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.

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.

Definition

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

Addressing Modes

Basic Addressing ModesMost 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

OPR

OPCODE

MPC

MDR

IR

Immediate addressing (microcomputers)

Basic Addressing Modes

OPCODE OPR OPCODE OPR

PC

Immediate addressing (large computers)

IR

IR OPR

Implied addressing

(implied)


Reg.# 2IR Reg.# 2 (OPR)

Reg.# 1

Reg.# 3

Reg.# 4

Register addressing

OPCODE ADDR

OPR

M

PC

Direct addressing (large computers)

OPCODE

ADDR

OPR

MMAR

PC

Direct addressing (microcomputers)


Reg. # 1

Reg. # 2

Reg. # 3

OPR

M

OPCODE Reg. #2IR

Register indirect addressing

Reg. # 2 OPR

M

OPCODEIR(implied)

Implied register indirect addressing

OPCODE Reg. # 2

Index

Reg. # 3

Reg. # 2

Reg. # 2

OPR

M

IR

Indexed addressing

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


OPCODE offset

PC

offset

OPR

MIR

Relative addressing

Specified address

Base register

OPR

M

Base addressing


Page EA OPR

M

Page addressing

Page register

ADDR

OPR

M

EA

Indirect addressing

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 user’s 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.

Virtual Memory

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

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.

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.

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.

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.

Memory Organization

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.

Memory Access Time

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.

Memory Types

Applications of ROM: There are many

applications of ROMs, some of which include:

1. Permanent information storage

2. Code conversion

3. Multiple output function generation

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.

Read-Only 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.

Read/Write Memory

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.

RAM Types

1. John Y.Cheung, and Jon G.Bedeson , Modern Digital Systems

Design. New York : West Publishing Company, 1990.

2. Anthony J. Dos Reis , Assembly Language And Computer

Architecture Using C++ and Java. United States : Thomson

Course Technology, 2004.

References

Education

Rahman