COMPUTER ARCHITECTURES
Himansu Shekhar Pradhan
1
WHAT IS COMPUTER ARCHITECTURE?
Computer architecture refers to those parameters of a computer system that
are visible to a programmer
Or those parameters that have a direct impact on the logical execution of a
program.
Example: Instruction set, the number of bits used to represent different data
types, I/O mechanisms and techniques for addressing memory.
Technology
Hardware Organization
Parallelism
Computer
Architecture
Execution &
Evaluation
PL
Interface
Interface Design
OS
2
HISTORY OF COMPUTER EVOLUTION
Before VLSI technology (1945-1978)
ENIAC
IAS
IBM
PDP-8
After VLSI technology (1979-till date)
Microprocessors!!!!
3
EVOLUTION OF COMPUTER
FIRST GENERATION (1945-1954)
Program and data reside in the same memory (stored program
concepts – John von Neumann)
ALP was made used to write programs
Vacuum tubes were used to implement the functions (ALU & CU
design)
Magnetic core and magnetic tape storage devices are used
4
EVOLUTION OF COMPUTER
SECOND GENERATION (1955-1964)
Transistor were used to design ALU & CU
HLL was used (FORTRAN)
To convert HLL to MLL compilers were used
Separate I/O processors were developed to operate in parallel
with CPU, thus improving the performance
Invention of the transistor which was found so that it required
considerably less power to operate
5
EVOLUTION OF COMPUTER
THIRD GENERATION (1965-1974)
IC technology improved
Improved IC technology helped in designing low cost, high speed processor
and memory modules
Multiprogramming, pipelining concepts were incorporated
DOS allowed efficient and coordinate operation of computer system with
multiple users
Cache and virtual memory concepts were developed
More than one circuit on a single silicon chip became available
6
EVOLUTION OF COMPUTER
FOURTH GENERATION (1975-1984)
CPU – Termed as microprocessor
INTEL, MOTOROLA, TEXAS, NATIONAL semiconductors started
developing microprocessor
Workstations, microprocessor (PC) & Notebook computers were
developed
Interconnection of different computer for better communication
LAN,MAN,WAN
Computational speed increased by 1000 times
Specialized processors like Digital Signal Processor were also
developed
7
EVOLUTION OF COMPUTER
BEYOND FOURH GENERATION (1985 TO TILL DATE)
E‐Commerce, E‐ banking, home office
ARM, AMD, INTEL, MOTOROLA
High speed processor ‐ GHz speed
Because of submicron IC technology lot of added features in
small size
8
TYPES OF COMPUTERS
Computers are classified based on the following
parameters
Speed of operation
Cost
Computational power
Type of application
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TYPE OF COMPUTERS
DESKTOP
NOTEBOOK
WORK STATIONS
ENTERPRISE SYSTEM (MAINFRAME)
SERVER SYSTEM
SUPER COMPUTERS
HANDHELD
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DESKTOP COMPUTER
Processing &storage units, visual display &
audio units, keyboards
Storage media‐Hard disks, CD‐ROMs
Personal computers which is used in homes and
offices
Advantage: Cost effective, easy to operate,
suitable for general purpose educational or
business application
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NOTEBOOK COMPUTER
Compact form of personal computer
(laptop)
Advantage is portability (Types of
application)
12
WORKSTATIONS
More computational power than PC
Costlier
Used to solve complex problems which
arises in engineering application (graphics,
CAD/CAM etc)
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ENTERPRISE SYSTEM (MAINFRAME)
More computational power
Larger storage capacity
Used for business data processing in large
organization
Sometimes it can be used as servers or
super computers
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SERVER SYSTEM
Supports large volumes of data
which frequently need to be accessed
or to be modified (Types of
application)
Supports request response operation
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SUPER COMPUTERS
Faster than mainframes
Helps in calculating large scale
numerical and algorithm calculation in
short span of time
Used for aircraft design and testing,
military application and weather
forecasting etc.
16
HANDHELD
Also called a PDA (Personal Digital Assistant)
A computer that fits into a pocket, runs on batteries,
and is used while holding the unit in your hand
Typically used as an appointment book, address book,
calculator, and notepad (Types of application)
Can be synchronized with a personal microcomputer
as a backup
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BASIC TERMINOLOGY
Input
–
Whatever is put into a computer system.
Data
–
Refers to the symbols that represent facts, objects, or ideas.
Information
–
The results of the computer storing data as bits and bytes, the words,
numbers, sounds, and graphics.
Output
–
Consists of the processing results produced by a computer.
Processing
–
Manipulation of the data in many ways.
Memory
–
Area of the computer that temporarily holds data waiting to be
processed, stored, or output.
Storage
–
Area of the computer that holds data on a permanent basis when it is not
immediately needed for processing.
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BASIC TERMINOLOGY CONT.
Assembly language program (ALP) – Programs are
written using mnemonics
Mnemonic – Instruction will be in the form of English
Assembler – is a software which converts ALP to MLL
(Machine Level Language)
HLL (High Level Language) – Programs are written
using English like statements
Compiler- Convert HLL to MLL, does this job by
reading source program at once
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BASIC TERMINOLOGY CONT.
Interpreter – Converts HLL to MLL, does this job
statement by statement
System software – Program routines which aid the user
in the execution of programs eg: Assemblers,
Compilers
Operating system – Collection of routines responsible
for controlling and coordinating all the activities in a
computer system
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COMPUTING SYSTEMS
Computers have two kinds of components:
Hardware, consisting of its physical devices
(CPU, memory, bus, storage devices etc.)
Software, consisting of the programs it has
(Operating system, applications, utilities
etc.)
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FUNCTION
IMPORTANT SLIDE !
The most important functions of computers are:
Data PROCESSING
Data STORAGE
Data=Information
Data MOVEMENT
CONTROL
Co-ordinate how the
operations have been done
NOTHING ELSE!!!!!
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BASIC COMPUTER MODEL
The model of a computer can be described by four basic units in
high level abstraction.
These basic units are:
Central Processor Unit
Input Unit
I/O
Output Unit
Devices
Memory Unit
CPU
O/P
Devices
Memory
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CENTRAL PROCESSOR UNIT (CPU)
Central processor unit consists of two basic blocks :
The program control unit has a set of registers and
control circuit to generate control signals
The execution unit or data processing unit contains
a set of registers for storing data and an
Arithmetic and Logic Unit (ALU) for execution of
arithmetic and logical operations
In addition, CPU may have some additional
registers for temporary storage of data
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INPUT UNIT
Data from outside can be supplied to the
computer with the help of input unit
Program or data is read into main storage or
secondary storage from input device under the
control of CPU input instruction
Example of input devices: Keyboard, Mouse, Hard
disk, Floppy disk, CD-ROM drive etc.
25
OUTPUT UNIT
Computer results can be provided to the user or it
can be stored in storage device permanently for
future use with the help of output unit
Output data from main storage go to output
device under the control of CPU output instructions
Example of output devices: Printer, Monitor, Hard
Disk, Floppy Disk etc.
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MEMORY UNIT
Memory unit is used to store the data and program
CPU can work with the information stored in memory
unit
This memory unit is termed as primary memory or
main memory module
These are basically semi conductor memories
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MEMORY UNIT CONT.
There are two types of semiconductor memories
Volatile Memory:
RAM (Random Access Memory)
Non-Volatile Memory:
ROM (Read only Memory)
PROM (Programmable ROM)
EPROM (Erasable PROM)
EEPROM (Electrically Erasable PROM)
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MEMORY UNIT CONT.
Secondary Memory:
Secondary memories are non-volatile memory
it is used for permanent storage of data and program
Example of secondary memories:
Hard Disk, Floppy Disk, Magnetic Tape ------ These are
magnetic devices
CD-ROM ------ is optical device
Thumb drive (or pen drive) ------ is semiconductor
memory
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MEMORY
MEMORY HIERARCHY
The memory unit is an essential component in any digital
computer since it is needed for storing programs and
data.
Not all accumulated information is needed by the CPU at
the same time
Therefore, it is more economical to use low-cost storage
devices to serve as a backup for storing the information
that is not currently used by CPU
MEMORY HIERARCHY
Memory Hierarchy is a pyramid structure that is commonly used
to illustrate the significant differences among memory types
The memory unit that directly communicate with CPU is called
the main memory
Devices that provide backup storage are called auxiliary
memory
The memory hierarchy system consists of all storage devices
employed in a computer system
Slow but high-capacity----Auxiliary memory
A relatively faster----Main memory
A faster and smaller----Cache memory
MEMORY HIERARCHY
MAIN MEMORY
Main memory in a general purpose computer is referred as
RAM integrated circuits chips
However, a portion of the memory may be constructed with
ROM chips
RAM– Random Access memory
RAMs are available in two possible operating modes i.e.
Static and Dynamic
ROM– Read Only memory
RAM
A RAM chip has one or more control inputs that select
the chip when needed Read/write memory
The memory system used to store data at various
locations and retrieve it later from these locations
It has bidirectional data pins (data can flow into or
out of the chip via these pins), unlike to ROM that it
has output only
It loses its data once the power is removed therefore,
it is a volatile memory
RANDOM ACCESS MEMORY TYPES
Static RAM (SRAM)
 Each cell stores bit with a six-transistor circuit
 Retains value indefinitely, as long as it is kept powered
 Relatively insensitive to disturbances such as electrical
noise.
 Faster and more expensive than DRAM.
Dynamic RAM (DRAM)
 Each cell stores one bit with a capacitor and transistor.
 Value must be refreshed every 10-100 ms
 Sensitive to disturbances.
 Slower and cheaper than SRAM.
PO IN DYNAMIC RAM (DRAM)
PO IN DYNAMIC RAM (DRAM)
DRAM
Made with cells that store data as charge on
capacitors
Presence or absence of charge in a capacitor is
interpreted as a binary 1 or 0
Requires periodic charge refreshing to maintain
data storage
The term dynamic refers to tendency of the
stored charge to leak away, even with power
continuously applied
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PO IN STATIC RAM (SRAM)
PO IN STATIC RAM (SRAM)
SRAM
SRAMs are simply integrated circuits that are
memory arrays with (usually) a single access port
that can provide either a read or a write
SRAMs have a fixed access time to any datum,
though the read and write access times may differ
SRAMs don’t need to refresh and so the access
time is very close to the cycle time
SRAM needs only minimal power to retain the
charge in standby mode
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SRAM VERSUS DRAM
Both volatile
 Power must be continuously supplied to the memory to preserve the
bit values
Dynamic cell
 Simpler to build and smaller
 More dense (smaller cells = more cells per unit area)
 Less expensive
 Requires the supporting refresh circuitry
 Tend to be favoured for large memory requirements
 Used for main memory
Static
 Faster
 Used for cache memory (both on and off chip)
ROM
ROM is used for storing programs that are
PERMANENTLY resident in the computer
The tables of constant do not change it’s value
once the production of the computer is
completed
The ROM portion of main memory is needed
for storing an initial program called bootstrap
loader
Which is used to start the computer software
operating when power is turned off
ROM TYPES
Masked ROM – programmed with its data when the chip is
fabricated
PROM – Programmable Read Only Memory: it can be
programmed once as per user requirements
EPROM – Erasable Programmable Read Only Memory: the
contents of the memory can be erased and store new data
into the memory. In this case, we have to erase whole
information.
EEPROM – Electrically Erasable Programmable Read Only
Memory: in this type of memory the contents of a particular
location can be changed without affecting the contents of
other location.
PHYSICAL MEMORY TYPES
Memory Type
Random-access
memory (RAM)
Read-only
memory (ROM)
Programmable
ROM (PROM)
Category
Read-write
memory
Read-only
memory
Erasable PROM
(EPROM)
Electrically
Erasable PROM
(EEPROM)
Flash memory
Erasure
Electrically,
byte-level
Write
Mechanism
Electrically
Volatile
Masks
Not possible
UV light, chiplevel
Read-mostly
memory
Volatility
Electrically,
byte-level
Electrically,
block-level
Nonvolatile
Electrically
PROGRAMMABLE ROM (PROM)
Less expensive alternative
Nonvolatile and may be written into only once
Writing process may be performed by
supplier or customer at a time later than the
original chip fabrication
Special equipment is required for the writing
process
Provides flexibility and convenience
Attractive for high volume production runs
READ-MOSTLY MEMORY
EPROM
EEPROM
Erasable programmable
read-only memory
Electrically erasable
programmable readonly memory
Erasure process can be
performed repeatedly
More expensive than
PROM but it has the
advantage of the multiple
update capability
Can be written into at
any time without
erasing prior contents
Combines the advantage
of non-volatility with the
flexibility of being
updatable in place
More expensive than
EPROM
Flash
Memory
Intermediate between
EPROM and EEPROM in
both cost and
functionality
Uses an electrical
erasing technology,
does not provide bytelevel erasure
Microchip is organized so
that a section of memory
cells are erased in a
single action or “flash”
WHY CACHE MEMORY?
Analysis of large number of programs has shown that a
number of instructions are executed repeatedly
This may be in the form of simple loops, nested loops, or a
few procedures that repeatedly call each other
Many instructions in each of a few localized areas of the
program are repeatedly executed, while the other area of
the program is accessed relatively less
This phenomenon is referred to as locality of reference
47
WHY CACHE MEMORY?
CPU is a faster device and memory is a relatively
slower device
Memory access is the main bottleneck for the
performance efficiency
To make this arrangement effective, the cache must be
considerably faster than the main memory
Typically it is 5 to 10 time faster than the main
memory
This approach is more economical than the use of fast
memory device to implement the entire main memory
This is also a feasible due to the locality of reference
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CACHE MEMORY
❑Cache memory is a small, high-speed RAM buffer located
between the CPU and main memory.
❑Cache memory holds a copy of the instructions (instruction
cache) or data (operand or data cache) currently being used
by the CPU.
❑The main purpose of a cache is to accelerate your computer
while keeping the price of the computer low.
PLACEMENT OF CACHE IN COMPUTER
OPERATION OF CACHE MEMORY
The memory control circuitry is designed to take advantage
of the property of locality of reference
Some assumptions are made while designing the memory
control circuitry:
1. The CPU does not need to know explicitly about the
existence of the cache.
2. The CPU simply makes Read and Write request. The
nature of these two operations is same whether cache is
present or not
3. The address generated by the CPU always refers to
location of main memory.
4. The memory access control circuitry determines whether
or not the requested word currently exists in the cache.
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OPERATION OF CACHE MEMORY
When a Read request is received from the CPU, the
contents of a block of memory words containing the
location specified are transferred into the cache
When any of the locations in this block is
referenced by the program, its contents are read
directly from the cache
The cache memory can store a number of such
blocks at any given time
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OPERATION OF CACHE MEMORY
When a write request is received from the CPU,
there is a way that the system can proceed
In this process, the cache location and the main
memory location are updated simultaneously
The correspondence between the Main Memory
Blocks and those in the cache is specified by
means of a mapping function
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TYPES OF CACHE MAPPING
Direct mapping:
A particular block of main memory can be brought to a
particular block of cache memory. So, it is not flexible.
Associative mapping:
In this mapping function, any block of Main memory can
potentially reside in any cache block position. This is much more
flexible mapping method.
Block-set-associative mapping:
In this method, blocks of cache are grouped into sets, and the
mapping allows a block of main memory to reside in any block
of a specific set. From the flexibility point of view, it is in between
to the other two methods.
DIRECT MAPPING
The direct mapping technique is simple and inexpensive to
implement.
When the CPU wants to access data from memory, it places a
address.
The index field of CPU address is used to access address.
The tag field of CPU address is compared with the associated
tag in the word read from the cache.
If the tag-bits of CPU address is matched with the tag-bits of
cache, then there is a hit and the required data word is read
from cache.
If there is no match, then there is a miss and the required data
word is stored in main memory. It is then transferred from main
memory to cache memory with the new tag.
DIRECT MAPPING
Example:
Consider a cache of 4096 (4K) words with a block size of
32 words. Therefore, the cache is organized as 128 blocks.
For 4K words, required address lines are 12 bits.
To select one of the blocks out of 128 blocks, we need 7
bits of address lines and to select one word out of 32
words, we need 5 bits of address lines.
So the total 12 bits of address is divided for two groups,
lower 5 bits are used to select a word within a block, and
higher 7 bits of address are used to select any block of
cache memory.
56
DIRECT MAPPING
Example:
Let us consider a main memory system consisting 64K words.
The size of address bus=16 bits
Since the block size of cache is 32 words, so the main memory
is also organized as block size of 32 words
Therefore, the total number of blocks in main memory is 2048
(2K x 32 words = 64K words)
To identify any one block of 2K blocks, we need 11 address
lines
Out of 16 address lines of main memory, lower 5 bits are used
to select a word within a block and higher 11 bits are used to
select a block out of 2048 blocks
57
DIRECT MAPPING
DIRECT MAPPING