Computer

?What is a Computer？

a device that accepts input, processes data, stores data, and produces output, all according to a series of stored instructions

–Input includes words and symbols, numbers, pictures, audio signals, instructions, and so on. –Data refers to the symbols that represent facts, objects, and ideas.

–Computers manipulate data in many ways, and this manipulation is called processing.

–Most computers have more than one location for storing data.

?Memory is an area that temporarily holds data that is waiting to be processed, stored, or output.

?Storage is the area that permanently holds data that is not immediately needed for processing. –Output is the result produced by a computer, for example reports, documents, music, graphs, pictures, and so on.

–The series of instructions that tells a computer how to carry out processing tasks is referred to as a computer program.

? The Evolution of Computer

–The first electronic computer was the Electronic Numerical Integrator And Computer

(ENIAC). –It became operational in 1946.

–It contained 18,000 light-bulb-size electronic vacuum tubes.

–It weighed 30 tons and occupied about 1800 square feet of floor space. –It could perform 5000 additions per second.

?First Generation (1946---1958)

?Main memory was almost made up of hundreds of vacuum tubes. ?Most input and output media were punched cards and magnetic tape.

?Second Generation(1959---1963)

?Transistors and some other solid-state devices were being used for the computer circuitry. (A transistor is an electronic switch that alternately allows or does not allow electronic signals to pass.)

?Magnetic cores became the most widely used type of main memory.

?Removable magnetic disk packs, stacks of disks connected by a common spindle were introduced as storage devices.

?High-level languages were available for use.

?Third Generation(1964---1970)

?The integrated circuit (IC) replaced traditional transistorized circuitry.

(IC is a complete electronic circuit that packages transistors and other electronic components on a small silicon chip.)

?The use of magnetic disks for secondary data became widespread.

?Computers began to support multiprogramming (processing several programs at the same time).

?Fourth Generation(1971---Now)

?Large-scale integrated (LSI) and very-large-scale integrated (VLSI) circuits were developed.

(contained hundreds to millions of transistors on a tiny chip) ?In 1971 the microprocessor was developed, which

packaged an entire CPU, complete with memory, logic, and control circuits, on a single chip.

?Computer’s main memory capacity increased, and its cost decreased.

?Computer Categories

–Supercomputers www.top500.org ? the fastest and highest-capacity computers

? have hundreds to thousands of processors

? can perform trillions of calculations per second

–Mainframe computers

? fast, mid- to large-size, large-capacity

? simultaneously processing data for hundreds or thousands of user

? main processing circuitry is housed in a closet-sized cabinet and have many processors

–Workstations

?tackle tasks that require a lot of processing speed ?some contain more than one microprocessor

?most have circuitry specially designed for creating and displaying three-dimensional and

animated graphics –Server

?serve the computers on a network by supplying them with data ?especially suited for storing and distributing data on a network

–Microcomputers (Personal Computers, PC)

?designed to meet the computing needs of an individual

?provides access to a wide variety of computing applications, such as word processing ?desktop computer and notebook computer

?Computer System –Hardware

the electronic and electromechanical parts consists of the following:

? Input Keyboard, Mouse, Scanner ? Memory and Storage

? Processing CPU (Central Processing Unit) ? Output Monitor, Printer

–Software

the instructions that tell the hardware how to perform a task ; a set of computer programs Without software, the hardware is useless. ? System Software

designed to allow the computer to manage its own resources and run the hardware and basic operations

? Application Software

performs tasks to directly benefit or assist the user

–Data and Information

?The primary purpose of computer systems in most businesses today is to transform data into

information that can be used by people. ?Data is used by computer.

information is used by humans. Data Representation

?Binary Number System

–Most computers are digital devices. A digital device works with discrete data. –The binary system has only two digits: 0 and 1 –bit (binary digit) each 0 and 1 is called a bit.

–Bits can be grouped in various combinations to represent data, such as numbers, letters,

punctuation marks, music, pictures, and videos.

?Represent numbers

–In binary, you run out of digits after you count to 1. To get to the next number, you have to use

the 0 as a place holder and the 1 indicates one group of 2s. –Octal and Hexadecimal number system

–Convert decimal numbers into binary numbers

divided by 2 until quotient becomes 0, all remainders are combined from the bottom up

–Convert binary numbers into decimal numbers

multiply the place value by each binary digit, form the sum of all digits In the binary number system the place values are powers of 2

?Represent characters (Binary Coding Schemes)

–ASCII (American Standard Code for Information Interchange)

? uses 7 bits for each character

? provides codes for 128 (27) characters

? the most widely used code with non-IBM mainframes and virtually all microcomputers ?Extended ASCII uses 8 bits

–EBCDIC (Extended Binary-Coded Decimal Interchange Code)

? 8-bit code, can represent 256 (28) characters ? used by IBM mainframe computers

–Unicode

? uses 16 bits for each character

? provides codes for 65536(216) characters

? can represent the alphabets of multiple languages, such as Chinese

?Represent sounds and pictures

–A computer must digitize colors, notes, and instrument sounds into 1s and 0s.

–Computers convert colors and sounds into numbers, which can be represented by bits.

?Terms

?bit (b): the smallest unit

transmission speeds are expressed in bits ?byte (B): 8 bits

storage space is usually expressed in bytes

10

?kilobyte (KB): =1024 B =2B

20

?megabyte (MB): =1024 KB =2B

30

?gigabyte (GB): =1024 MB =2B

40

?terabyte (TB): =1024GB =2B

Computer Hardware Hardware System

System Unit System board

–Some chips are permanently soldered in place. Other chips are plugged into special sockets and connectors.

–When multiple chips are required for a single function, the chips might be gathered together on a separate small circuit board, which can be plugged into a special slot-like connector. Microprocessor ?Basics

–A microprocessor is an integrated circuit designed to process instructions.

–The processor circuitry is etched on a thumbnail-size or slightly larger chip of silicon. The chip is mounted on a carrier with metal pins, on the bottom that plug into the computer’s motherboard.

–The processor consists of two parts: ? Arithmetic Logic Unit ? Control Unit

–The ALU performs arithmetic operations and logical operations.

?Arithmetic operations are the fundamental math operations: addition, subtraction, multiplication, and division.

?Logical operations are comparisons. The ALU compares two pieces of data to see whether one is “equal to” (=), “greater than” (>), or “less than” (<) the other.

–The control unit tells the rest of the computer system how to carry out a program’s instructions.

?It directs the movement of electronic signals between main memory and the ALU.

?It also directs these electronic signals between main memory and the input and output devices.

?Performance Factors –Processing Speed

?Every computer contains a system clock---an internal timing device that sets the pace for executing instructions.

?A machine cycle is the smallest unit of time in a microprocessor’s universe. Every action that a