Memory
Farhana Rahman
December 7th , 2004
CS147, SECTION 3
Outline
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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.
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.
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
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:
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Implied addressing
Immediate addressing
Register Addressing
Direct Addressing
Register indirect addressing
Implied register indirect addressing
Indexed addressing
Basic Addressing Modes
Immediate addressing (microcomputers)
Implied addressing
PC
(implied)
IR
OPR
M
IR
OPCODE
OPR
MDR
Immediate addressing (large computers)
PC
IR
OPCODE
OPR
OPCODE
OPR
Basic Addressing Modes
Register addressing
Direct addressing (large computers)
M
Reg.# 1
IR
Reg.# 2
PC
Reg.# 2 (OPR)
OPCODE
Reg.# 3
OPR
Reg.# 4
Direct addressing (microcomputers)
M
PC
OPCODE
ADDR
OPR
MAR
ADDR
Basic Addressing Modes
Register indirect addressing
IR OPCODE
Reg. #2
Reg. # 1
M
Reg. # 2
OPR
Reg. # 3
Implied register indirect addressing
M
IR
OPCODE
(implied)
Reg. # 2
OPR
Indexed addressing
Reg. # 2
M
IR
OPCODE
Reg. # 2
Index
Reg. # 3
OPR
Reg. # 2
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:
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Relative addressing
Base addressing
Page addressing
Indirect addressing
Special Addressing Modes
Relative addressing
PC
M
IR
OPCODE
offset
OPR
offset
Base addressing
Specified address
M
OPR
Base register
Special Addressing Modes
Page addressing
M
Page
EA
OPR
Page register
Indirect addressing
M
EA
ADDR
OPR
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 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.
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 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.
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 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.
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.
Read-Only Memory
 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/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.
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.
References
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.