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Unit-1
An overview of Computer
System
Anatomy of a digital Computer
Definition of Computer
• A device that accepts data, processes
the data in accordance with a stored
program, generates results, and usually
consists of input, output, storage,
arithmetic, logic, and control units.
• A machine for manipulating data
according to a list of instructions
known as a program.
…cntd
Block Diagram of Digital Computer
Random-access memory
(RAM)
Central processing unit
(CPU)
Input
devices
Input-output processor
(IOP)
Output
devices
Block diagram of a digital computer
Block Diagram of Digital Computer
• A digital computer consists of a number of
processors interconnected with memory and
Input/Output devices
• A Processor or CPU (Central Processing
Unit) fetches instructions from memory, and
executes them one after another
• A Memory is where programs and data are
stored
• I/O devices allow for interaction between
users and computer (printers, keyboard,
mice… )
Generations of Computers
• First generation: Vacuum tube
computers (1940s - 1950s)
• First Generation Electronic
Computers used Vacuum Tubes
• Vacuum tubes are glass tubes with
circuits inside.
• Vacuum tubes have no air inside
of them, which protects the
circuitry.
Generations of Computers
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Second generation (1950s): Transistors
Uses Silicon
developed in 1948
won a Nobel prize
on-off switch
Second Generation Computers used
Transistors, starting in 1956
• Replaced vacuum tubes with Transistors
Generations of Computers
• Third generation (1960s and 1970s): Integrated
circuits
• Third Generation Computers used Integrated
Circuits (chips).
• Integrated Circuits are transistors, resistors, and
capacitors integrated together into a single “chip”
• Operating System
• Software – Instructions for Computer
• Operating system is set of instructions loaded each
time a computer is started
• Program is instructions loaded when needed
Generations of Computers
• Fourth generation (late 1970s through
present): LSI and VLSI
– Personal computers, computer networks,
WWW, etc.
• The First Microprocessor – 1971-Intel
4004 Microprocessor
• The 4004 had 2,250 transistors
• 108Khz
• Called “Microchip”
Generations of Computers
• Very Large Scale Integrated Circuit
(VLSIC)
– Transistors, resistors, and capacitors
• 4004 had 2,250 transistors where
• Pentium IV has 42 MILLION transistors
Generations of Computers
• Fifth generation- 21st Century Computing
• Great increases in speed, storage, and
memory
• Increased networking, speed in Internet
• PDAs
• Cell Phone/PDA
• WIRELESS!!!
Major Hardware Components of a
Computer System
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CPU
Main Memory
Secondary Memory
Input Devices
Output Devices
Central Processing Unit
• Control Unit: works with the operating system to
move data between auxiliary storage and main
memory; and between main memory and the ALU
• Arithmetic/Logic Unit (ALU): processes data
arithmetically (addition, subtraction, multiplication,
division) or logically (greater than, less than, equal
to)
• Main Memory: contains both program instructions
and the data that is required.
• A single machine can have multiple CPUs to share
processing tasks (co-processors, multiprocessing),
but each CPU can execute only a single task.
Inside the System Unit
• Main component: motherboard
– Circuit board that “houses” integrated
circuits (microscopic elements … wires,
transistors, etc…) required to make the
digital pulse flow inside of the computer.
Pulses flow from component to
component via the “bus”
Motherboard (cont.)
– Attachments to the motherboard include:
• Main Memory: types of main memory include:
– RAM - temporary (includes virtual memory
storage). Include RAM cache
– ROM - permanent
– When add main memory, make sure add-on chips
are compatible
• Real time clock (current date and time)
• Microprocessor or CPU (central processing unit)
– Control Unit: traffic cop portion of the CPU
– ALU: arithmetic logic unit processes all math and
logical operations performed by the computer
Primary & Secondary Storage Media
Semiconductor
Memory
Magnetic
Disks
Floppy Disk
Hard Disk, RAID
Magnetic Tape
Optical Disks
CD-ROM, CD-R
CD-RW
DVD
Direct
Access
Sequential
Access
Direct
Access
Memory Units- a unit for measuring computer
memory
• Unit - any division of quantity accepted as a
standard of measurement or exchange; "the dollar is
the United States unit of currency"; "change per unit
volume"
• Nibble - a small byte
• Byte - a sequence of 8 bits (enough to represent one
character of alphanumeric data) processed as a
single unit of information
Memory Units
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• Sector - the minimum track length that can
be assigned to store information; unless
otherwise specified a sector of data consists
of 512 bytes
• Block - a sector or group of sectors that
function as the smallest data unit permitted;
"since blocks are often defined as a single
sector, the terms `block' and `sector' are
sometimes used interchangeably"
Main Memory
• Stores Instructions and Data
– Stored Program Concept
• Random Access Memory (RAM): allows data and
instructions to be accessed randomly from any memory
location (address). Primary storage.
– Volatile - lost when power is turned off
• Read Only Memory (ROM): usually contains programs that
help the computer system operate:
– can only be read: cannot be written to or altered by the
user (usually)
– ROM is not volatile
Main Memory
• Data and instructions are stored as BITS (binary digits).
Everything from our world is translated into a computer
recognizable format called binary (zeros or ones)
– The combination of binary digits represents our letters or
numbers. One character represented is equal to a byte.
• Memory capacity is measured in bytes. Today’s most
common measurement is megabytes
Kilo = 1,000 (KB) Thousand
Mega = 1,000,000 (MB) Million
Giga = 1,000,000,000 (GB) Billion
• Bytes are composed using either the ASCII coding system
(7 bits = character) or EBCDIC (8 bits = character)
Input Devices
• Input Devices are used to input the data to
computer system. These are as follows

Keyboard

Mouse

Trackball

Touch Screen

Optical Character Recognition

MICR

Scanners etc.
Output Devices
• Output Devices are used to take output
from computer system. These are as follows
Monitor
Printer
Plotter