Computer system architecture

Computer System Architecture
Unit-I
From : Hitesh Kumar Sharma
CIT, UPES

Evolution of computers
» Pre- first generation (mechanical /non-electronic
computers)
» Electronic computers

Evolution of computers
Generation

Technology

Software apps/
Representing systems

First Generation
(1945-54)

Vacuum
tubes, relays, ALU

Machine/assembly languages
ENIAC, IBM701

Second Generation
(1955-64)

Transistors,
memories, IO
processors

HLL, Batch processing
IBM7090

Third Generation
(1965-74)

IC s SSI , MSI,
Micro programming

Multiprogramming/Time
sharing OS, Intel 8008

Fourth Generation
(1975-84)

LSI & VLSI

Multiprocessor OS
IBM PC

Fifth Generation
(1984-90)

VLSI, ULSI
multiprocessors

Parallel computing
IBM PC AT, Intel 486

Sixth Generation
(1990 onwards)

ULSI, VHSIC, high
density packing,
scalable architecture

Massively parallel processing/
Pentium, Sun Ultra Workstation

Moore’s Law
Moore's law is the
observation that “number of
transistors per square inch
on integrated circuits had
doubled every 18months
since the integrated circuit
was invented”.
The period often quoted as
"18 months" is due to Intel
executive David House, who
predicted that period for a
doubling in chip performance
(being a combination of the
effect of more transistors and
their being faster).

The ENIAC computer required more than
17,000 vacuum tubes to perform ballistic
calculations in decimal (base-10) notation.
Although vacuum tubes were better than
electromechanical relays, the tubes overheated and needed frequent replacements.

Computers categories
 Computers for Individual Users (PC)






Desktop Computers
Notebook computers
Tablet computers
Handheld computers
Smart phones

 Computers for Organizations





Servers
Network servers
Mainframe computers
Super computers

Super Computer

The Blue Gene/P supercomputer at Argonne National Lab runs over 250,000
processors using normal data center air conditioning, grouped in 72 racks/cabinets
connected by a high-speed optical network[1]

Computer Components – looking inside
 Hardware
 Software
 Data

Hardware
 Processor - CPU
 Memory –
 RAM – Random Access Memory
 ROM - Read Only Memory
Memory Size measured in KB, MB, Kb, Mb, GB

 Input Devices
Keyboard, mouse, barcode readers
, touchscreens, microphone

 Output Devices
Monitor, display devices, printers, speakers,

 Storage (external memory)
Hard disk, CD, USB /pen drive, SD/micro memo
cards, memory tapes, zip drive

Computer interface with IO devices:
Ports

Communications and Ports
Computers are connected to external devices via I/O connectors at
the back of the computer. Depending on the device being
connected and the cable being used, the device may be connected
via a serial port (either 9 or 25 pin connector) or via a 25 pin parallel
port.

PS/2 Ports
Desktop computers often have two PS/2 connectors where the
keyboard and mouse are attached. The connectors are identical,
but often colour coded -- blue is keyboard and green is mouse. In
future, PS/2 ports are likely to be replaced by USB.

• VGA Port
A VGA port is used to connect a monitor to
a computer. On the back of the computer,
should be a female 15-pin connector.

• USB Ports
There are two Universal Serial Bus (USB) standards, USB 1.1
and USB 2.0. USB connectors and adapters allow the
connection of up to 127 peripheral devices. USB 1.1 can
transmit data at a rate of 12 Mbps. but USB 2.0 (sometimes
called High-speed USB) can transmit at 480 Mbps
Fire Wire Port
preferred standard for very high speed communications - the IEEE1394 standard. Data is transferred at speeds of
up to 400 Mbps (in IEEE 1394a standard) and 800 Mbps
(in IEEE 1394b standard). Fire wire allows up to 63
devices to be connected
Network Connection
A network jack is used to connect a computer's
network card to a cable modem or to the network.

Processor interaction with devices
• Device Addressing
 Memory mapped IO
 Port mapped IO

• Interrupts
• Device Drivers – OS

Storage= store data
Storage types based on Technology
I.
II.
III.

Semiconductor – (IC) – RAM, ROM, Flash
Magnetic – HD, Tape, Floppy
Optical - CD ROM, DVD ROM

Storage types based on Volatility
1. Volatile
2. Nonvolatile

Storage Types based on computer access
I.
II.

Primary – Main memory, RAM and ROM
Secondary – Hard disk, CD ROM

Primary Storage
– is also main memory or internal memory – is directly
accessible to CPU
– CPU stores instructions and executes in main memory
– Main memory is connected to CPU using memory bus.
Memory bus has 2 bus internally – address bus and
data bus
– RAM and ROM are main memories. RAM is temporary
or volatile data. ROM stores startup program (BIOS)
which is permanent and uses non-volatile technology.

Secondary Storage
– Also called as ‘auxiliary storage’ is memory that is
not directly accessible by CPU but a majority of
data and programs stored
– All storage that is not required in primary memory
is secondary storage
– Normally accessed by CPU using IO channels
– Eg. Hard disk, CD ROM

Volatility
• Non-volatile memory Will retain the stored information even if it is not
constantly supplied with electric power. It is suitable for long-term storage
of information.
• Volatile memory Requires constant power to maintain the stored
information. The fastest memory technologies of today are volatile ones
generally. Since primary storage is required to be very fast, it
predominantly uses volatile memory.
– Dynamic random-access memory: A form of volatile memory which also
requires the stored information to be periodically re-read and re-written, or
refreshed, otherwise it would vanish.
– Static random-access memory A form of volatile memory similar to DRAM
with the exception that it never needs to be refreshed as long as power is
applied. (It loses its content if power is removed).
Is BIOS volatile or nonvolatile ?

Storage Device characteristics
•
•
•
•
•

Volatility - Volatile or non-volatile
Accessibility – Sequential access or random access
Addressability – memory or file addressable
Capacity – size and density
Latency - Time taken to access data from particular location

Key Terms
•
•
•
•
•

RAM
ROM
Cache
Virtual Memory
Volatile and non-Volatile memory

CENTRAL PROCESSING UNIT (CPU)
• The central processing unit (CPU) is the portion of a
computer system that carries out the instructions of a
computer program, and is the primary element carrying
out the computer's functions.
• The form, design and implementation of CPUs have
changed dramatically since the earliest examples, but
their fundamental operation remains much the same.

Components of CPU
1.
2.
3.
4.
5.

ALU – Arithmetic Logic Unit
Registers
Control Unit
RAM
Buses
Instruction Register

Program Counter

Decoders
Multiplexor

RAM
ALU
Accumulator

Registers






Registers are memory
that are present within
CPU and can be
accessed very quickly
It’s content can be
easily and more
quickly accessed than
storage available
elsewhere.
Examples include the
instruction
register, flag
register, the program
counter and the
accumulator.

Control Unit
• A Control Unit is part
of the machinery
that controls its
operation.

• It Co-ordinates the
input and output
devices of a
computer system.

ALU
• ALU stands for
Arithmetic Logic
Unit.
• is a digital circuit that
performs arithmetic
and logical
operations.

Buses

• A bus is a subsystem that
transfers data between
computer components
• The buses are the
information highway for
the CPU.
• They are bundles of tiny
wires that carry data
between components.
• The three most important
buses are the
• address bus,
• data bus
• control buses.

Von Neumann architecture
Primary Memory

Input
Units

CPU
(Central Processing Unit)

Output
Units

– Programs and data are stored in the same
memory: primary memory.
– The computer can only perform one instruction
at a time.
– Most of modern and general purpose
computers/desktops follow this architecture

Computer system architecture

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Computer system architecture