Computer Systems Mr. McCullough AP Computer Science August 7, 2012 Quoth the College Board . . . A working knowledge of the major hardware and software components of computer systems is necessary for the study of computer science as is the importance of considering the ethical and social implications of computing systems . . . Section VI, AP Computer Science Outline Go to the College Board Website Major components of a computer • Central Processing Unit • Memory • Peripheral devices The central processing unit or microprocessor • Locates and executes program instructions • Carries out simple arithmetic • Retrieves data from storage and input/ output devices The Pentium 4 microprocessor Speed • Speed measured in Hz • Fastest Desktop? • The fastest computer in the world The price of speed . . . Dell IBM Apple Faster than a speeding bullet? Um, faster, actually . . . Storage • To manipulate stored data within a computer system, we must have a way of storing and retrieving it • Two types: – Primary – Secondary Primary Storage • RAM (Random Access Memory), • Data can be accessed in any “random” order • Holds the program code and data during execution Primary storage is electronic storage • No moving parts very fast! • Volatility Secondary storage – Includes magnetic tape and disks – More permanent More Secondary Storage Magnetic Tape A Hard Disk Pack DVDs ROM and ROM-BIOS • Read-Only Memory • Non-volatile • BIOS (Basic Input/ Output System) Loads operating System into RAM Some Peripheral Devices • Keyboard • Monitor • Speakers • Printer • Fax/modem • Mouse • Microphone And some more . . . Data Representation Data can be represented in two different forms • Analog: Represents continuously variable quantities that can fall anywhere on a continuum. • Digital: Can only represent a finite number of times. Digitalization and binary code • Computers are digital machines • Bits: fundamental units of information – Short for “binary digit” – “on” or “off” status Evolution of binary representation • Vacuum tubes • Transistors • Integrated Circuits • Microprocessors Stage I: Vacuum Tubes 1939-1954 First electronic “switches” Eniac, one of the world’s first computers Generation I: Vacuum Tubes Vacuum tube assembly The first computer bug. Generation II: Transistors 1954-1959 RCA transistor ad, from Fortune 1953/03 Generation III: Integrated Circuits 1959-1971 Integrated circuits placed all compon ents in one chip, drastically reducing Calculator, 1972 the size of the circuit and its components. Generation IV: The Microprocessor 1971-present • For more than 30 years, since the 1960's, the number of transistors per unit area has been doubling every 1.5 years. • Moore's law, after Gordon Moore, The Intel 4004 How is “on” or “off” represented? • In RAM: presence or absence of electrical charge • Disk: Magnetic arrangement of surface coating • CDs and CD-ROMS: Microscopic pits • Fiber optic cable: Pulses of light Binary representation and int How many possibilities can be conveyed? How about now? Binary representation and int How about now? Binary representation and int How about now? Bits and bytes • Bits are combined in an encoding system to represent letters • 8 bits in a byte • How many numbers < p> can be represented by one byte? Java and the 4-byte int Other “primitive” data types • double: 8 byte floating point number. • boolean: has only two possible values: true and false. • char: 2 bytes, stores a No offense. single character.
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