unit-1 an overview of computer system. anatomy of a digital computer definition of computer a device...
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Unit-1
An overview of Computer System
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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.
…cntd
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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
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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… )
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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.
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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
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• 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
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• 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
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• 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
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• 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
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Major Hardware Components of a Computer System
• CPU
• Main Memory
• Secondary Memory
• Input Devices
• Output Devices
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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.
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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”
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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
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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
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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"
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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
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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)
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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.
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• Output Devices are used to take output from computer system. These are as followsMonitorPrinterPlotter
Output Devices