Unit-1

An overview of Computer System

Anatomy of a digital ComputerDefinition 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.

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Block Diagram of Digital Computer

Random-access memory(RAM)

Central processing unit(CPU)

Input-output processor(IOP)

Inputdevices

Outputdevices

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.

• 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!!!

Generations of Computers

Major Hardware Components of a Computer System

• 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

SemiconductorMemory

SemiconductorMemory

MagneticDisks

Floppy DiskHard Disk, RAID

MagneticDisks

Floppy DiskHard Disk, RAID

Magnetic TapeMagnetic Tape

Optical DisksCD-ROM, CD-R

CD-RWDVD

Optical DisksCD-ROM, CD-R

CD-RWDVD

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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 ..cntd

• 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 are used to take output from computer system. These are as followsMonitorPrinterPlotter

Output Devices