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System Unit

System Unit. CS 104. Inside the System Unit. Computer Hardware Looking under the hood How computers represent data The Computer’s Brain : CPU Microprocessors : Computers on a Chip Bus : Freeway for Data Comparing CPUs Memory : Electronic Scratchpad. Computer Hardware. CPU Buses

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System Unit

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  1. System Unit CS 104

  2. Inside the System Unit • Computer Hardware • Looking under the hood • How computers represent data • The Computer’s Brain : CPU • Microprocessors : Computers on a Chip • Bus : Freeway for Data • Comparing CPUs • Memory : Electronic Scratchpad

  3. Computer Hardware CPU Buses Memory Keyboard Screen Printer

  4. How Computers Represent Data • Digital versus Analog Representation • Digital : High and Low Power Signals • Analog : Continuous variable scale • Numbering Systems • Every numbering system has a base • Regular (Decimal) is base 10 (0,1,2,….9) • Binary (Computers) is base 2 (0, 1)

  5. Binary Numbers • A binary number is called a binary digit or a bit • There are only 2 values for a bit, namely 0 and 1 • Every decimal number has a corresponding binary representation • Other common systems are base 16 (hexadecimal) and base 8 (octal)

  6. Decimal - Binary

  7. Data Representation in Computers • ASCII • American Standard Code for Information Interchange • EBCDIC • Extended Binary Coded Decimal Interchange Code • currently both are eight bit codes (byte) • representations are different

  8. ASCII and EBCDIC • Originally used a total of 7 bits • Encoded a total of 128 characters • Included letters, numbers & punctuation • Looking for a wider market • IBM and Apple expanded to 8 bits • Extended character sets are not standardized • Macintosh and PC versions differ

  9. Representing Data • Unicode • Expanded to 16 bits (65000 characters) • Can represent most languages and scripts • Parity • Extra bit added to coding systems • Used to ensure code is stored correctly • Odd and even parity

  10. Parity • Used when communicating across computers - extra bit is used if there has been a character transmission error • even parity - set the bit if the number of 1s is odd • odd parity - set the bit if the number of 1s is even

  11. Representing Digital Images

  12. A General Computer System

  13. The Computer’s Brain • CPU : Central Processing Unit • CPU is the brain of the computer • CPU = ALU + CU • ALU = Arithmetic and Logical Unit • CU = Control Unit • CPU co-ordinates and does all the work in a computer

  14. The Microprocessor • Contains the CPU • missing is memory, which usually comes on its own chips • needs customized software • US remains dominant • approaching limit of size • new area is 3-dimensional chips

  15. The Microprocessor • Data Bus • System Clock • Address Bus • CISC and RISC • Numeric Coprocessor

  16. Bus • Freeway for Data • Many of these are in the computer • Circuit that carries data from one component to another • The wider the bus, the more quickly the data can flow

  17. Data Bus • Path from the CPU to/from memory • internal - inside the CPU • external - to disk drives, etc • open bus - slots inside the PC • closed bus - ports

  18. Data Bus • 8088- 16-bit internal bus , 8-bit external • 80386SX - 32-bit internal bus, 16-bit external • 80386DX - 32-bit on both • 80486DX- 32-bit on both • 80486SX- 32-bit internal bus, 16-bit external • 80586 (Pentium) 64-bit on both

  19. System Clock • Device which emits a pulse at regular intervals • clock speed - # of times the clock “ticks” in one second • times is measured in megahertz (MHz) 1 million pulses

  20. Address Bus • Address - every storage location in computer memory has an address • set of wires connecting memory to the CPU is the address bus • size of bus determines the maximum address (storage) • maximum # of storage locations = width of address bus • 640K upper limit on RAM = 16 bit address bus

  21. Instruction Sets • Complex Instruction Set Computer (CISC) - Intel Pentium • Reduced Instruction Set Computer (RISC) - PowerPC • first computers were all hardwired - fast but hard to change • IBM devised microcode - simple software stored on the chip from which processors obtained instructions

  22. Instruction Sets • the extra HEFTY chunk of built in instructions in CISC is rarely used • RISC as the stripped down instruction set zips through programs • you can get speeds of four to ten times better on the RISC

  23. MMX • Set of 57 new instructions that apply primarily to multimedia programming • most popular set of instructions is the x86 but this may soon disappear with Intel’s new IA-64 instruction set architecture. (64-bit Merced(P7) processor) hopefully the new P7 will include complete support of x86

  24. Other Design Features • superscalar architecture (more than one instruction at a time), pipelining (simultaneous pathways), branch prediction, numeric coprocessor

  25. Numeric Coprocessor • Usually part of microprocessor design • speeds up numerical calculations

  26. CPU Compatibility • Compatibility • A program that can run on a computer • Downwardly Compatible • Runs programs designed for earlier chips • CPU sockets • Physically hold chips on motherboard • Established electrical connections

  27. Compatibility • program executability • programs are written for a specific processor • normally programs written for one processor will not execute on another • software emulator - program designed to emulate another environment • downwardly compatibility - old software can run on newer models

  28. Comparing CPUs • Data Bus Width and Word Size • Number of bits in bus determines word size • 16-bit CPU works with 16 bit word size • CISC (Complex Instruction Set Computer) • Many instructions & special purpose circuits • RISC (Reduced Instruction Set Computer) • Bare-bones instruction set

  29. Comparing CPUs • Multitasking • Processor runs more than one program • Pentium MMX • Contains 57 new instructions for multimedia • More quickly run games and multimedia • Benchmarks • Provides basis of comparison

  30. Questions ????

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