The Central Processing Unit: What Goes on Inside the Computer


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The Central Processing Unit: What Goes on Inside the Computer

  1. 1. The Central Processing Unit: What Goes on Inside the Computer Chapter 4
  2. 2. Objectives <ul><li>Identify the components of the central processing unit and how they work together and interact with memory </li></ul><ul><li>Describe how program instructions are executed by the computer </li></ul><ul><li>Explain how data is represented in the computer </li></ul><ul><li>Describe how the computer finds instructions and data </li></ul><ul><li>Describe the components of a microcomputer system unit’s motherboard </li></ul><ul><li>List the measures of computer processing speed and explain the approaches that increase speed </li></ul>
  3. 3. Contents <ul><li>The CPU </li></ul><ul><li>Types of Storage </li></ul><ul><li>Executing Programs </li></ul><ul><li>Finding Data in Memory </li></ul><ul><li>The System Unit </li></ul><ul><li>Microprocessor </li></ul><ul><li>Semiconductor Memory </li></ul><ul><li>Bus Line </li></ul><ul><li>Speed and Power </li></ul>
  4. 4. The CPU
  5. 5. The CPU <ul><li>Converts data into information </li></ul><ul><li>Control center </li></ul><ul><li>Set of electronic circuitry that executes stored program instructions </li></ul><ul><li>Two parts </li></ul><ul><ul><li>Control Unit (CU) </li></ul></ul><ul><ul><li>Arithmetic Logic Unit (ALU) </li></ul></ul>
  6. 6. Control Unit CU <ul><li>Part of the hardware that is in-charge </li></ul><ul><li>Directs the computer system to execute stored program instructions </li></ul><ul><li>Communicates with other parts of the hardware </li></ul>
  7. 7. Arithmetic / Logic Unit ALU <ul><li>Performs arithmetic operations </li></ul><ul><li>Performs logical operations </li></ul>
  8. 8. Arithmetic Operations <ul><li>Addition </li></ul><ul><li>Subtraction </li></ul><ul><li>Multiplication </li></ul><ul><li>Division </li></ul>+ - * /
  9. 9. Logical Operations <ul><li>Evaluates conditions </li></ul><ul><li>Makes comparisons </li></ul><ul><li>Can compare </li></ul><ul><ul><li>Numbers </li></ul></ul><ul><ul><li>Letters </li></ul></ul><ul><ul><li>Special characters </li></ul></ul>NOT AND OR > < >= <= = < >
  10. 10. Registers <ul><li>Special-purpose </li></ul><ul><li>High-speed </li></ul><ul><li>Temporary storage </li></ul><ul><li>Located inside CPU </li></ul>Instruction register Holds instruction currently being executed Data register Holds data waiting to be processed Holds results from processing
  11. 11. Types of Storage <ul><li>Secondary </li></ul><ul><ul><li>Data that will eventually be used </li></ul></ul><ul><ul><li>Long-term </li></ul></ul><ul><li>Memory </li></ul><ul><ul><li>Data that will be used in the near future </li></ul></ul><ul><ul><li>Temporary </li></ul></ul><ul><ul><li>Faster access than storage </li></ul></ul><ul><li>Registers </li></ul><ul><ul><li>Data immediately related to the operation being executed </li></ul></ul><ul><ul><li>Faster access than memory </li></ul></ul>
  12. 12. Measuring Storage Capacity <ul><li>KB – kilobyte </li></ul><ul><ul><li>1024 bytes </li></ul></ul><ul><ul><li>Some diskettes </li></ul></ul><ul><ul><li>Cache memory </li></ul></ul><ul><li>MB – megabyte </li></ul><ul><ul><li>Million bytes </li></ul></ul><ul><ul><li>RAM </li></ul></ul><ul><li>GB – gigabyte </li></ul><ul><ul><li>Billion bytes </li></ul></ul><ul><ul><li>Hard disks </li></ul></ul><ul><ul><li>CDs and DVDs </li></ul></ul><ul><li>TB – terabytes </li></ul><ul><ul><li>Trillion bytes </li></ul></ul><ul><ul><li>Large hard disks </li></ul></ul>
  13. 13. Memory Many Names <ul><li>Primary storage </li></ul><ul><li>Primary memory </li></ul><ul><li>Main storage </li></ul><ul><li>Internal storage </li></ul><ul><li>Main memory </li></ul>
  14. 14. Main Types of Memory <ul><li>RAM </li></ul><ul><li>Random Access Memory </li></ul><ul><li>ROM </li></ul><ul><li>Read Only Memory </li></ul>
  15. 15. RAM <ul><li>Requires current to retain values </li></ul><ul><li>Volatile </li></ul><ul><li>Data and instructions can be read and modified </li></ul><ul><li>Users typically refer to this type of memory </li></ul>
  16. 16. What’s in RAM? <ul><li>Operating System </li></ul><ul><li>Program currently running </li></ul><ul><li>Data needed by the program </li></ul><ul><li>Intermediate results waiting to be output </li></ul>
  17. 17. ROM <ul><li>Non-volatile </li></ul><ul><li>Instructions for booting the computer </li></ul><ul><li>Data and instructions can be read, but not modified </li></ul><ul><li>Instructions are typically recorded at factory </li></ul>
  18. 18. Executing Programs <ul><li>CU gets an instruction and places it in memory </li></ul><ul><li>CU decodes the instruction </li></ul><ul><li>CU notifies the appropriate part of hardware to take action </li></ul><ul><li>Control is transferred to the appropriate part of hardware </li></ul><ul><li>Task is performed </li></ul><ul><li>Control is returned to the CU </li></ul>
  19. 19. Machine Cycle <ul><li>I-time </li></ul><ul><li>CU fetches an instruction from memory and puts it into a register </li></ul><ul><li>CU decodes the instruction and determines the memory location of the data required </li></ul>
  20. 20. Machine Cycle <ul><li>E-time </li></ul><ul><li>Execution </li></ul><ul><ul><li>CU moves the data from memory to registers in the ALU </li></ul></ul><ul><ul><li>ALU is given control and executes the instruction </li></ul></ul><ul><ul><li>Control returns to the CU </li></ul></ul><ul><li>CU stores the result of the operation in memory or in a register </li></ul>
  21. 21. System Clock <ul><li>System clock produces pulses at a fixed rate </li></ul><ul><li>Each pulse is one Machine Cycle </li></ul><ul><li>One program instruction may actually be several instructions to the CPU </li></ul><ul><li>Each CPU instruction will take one pulse </li></ul><ul><li>CPU has an instruction set – instructions that it can understand and process </li></ul>
  22. 22. Finding Data in Memory <ul><li>Each location in memory has a unique address </li></ul><ul><ul><li>Address never changes </li></ul></ul><ul><ul><li>Contents may change </li></ul></ul><ul><li>Memory location can hold one instruction or piece of data </li></ul><ul><li>Programmers use symbolic names </li></ul>
  23. 23. Data Representation On/Off <ul><li>Binary number system is used to represent the state of the circuit </li></ul>1 0 ON OFF
  24. 24. Bits, Bytes, Words <ul><li>BIT </li></ul><ul><ul><li>B inary Dig IT </li></ul></ul><ul><ul><li>On/off circuit </li></ul></ul><ul><ul><li>1 or 0 </li></ul></ul><ul><li>BYTE </li></ul><ul><ul><li>8 bits </li></ul></ul><ul><ul><li>Store one alphanumeric character </li></ul></ul><ul><li>WORD </li></ul><ul><ul><li>Size of the register </li></ul></ul><ul><ul><li>Number of BITS that the CPU processes as a unit </li></ul></ul>
  25. 25. Coding Schemes <ul><li>ASCII </li></ul><ul><ul><li>Uses one 8 bit byte </li></ul></ul><ul><ul><li>2 8 = 256 possible combinations or characters </li></ul></ul><ul><ul><li>Virtually all PCs and many larger computers </li></ul></ul><ul><li>EBCDIC </li></ul><ul><ul><li>Uses one 8 bit byte </li></ul></ul><ul><ul><li>28 =256 possible combinations or characters </li></ul></ul><ul><ul><li>Used primarily on IBM-compatible mainframes </li></ul></ul><ul><li>Unicode </li></ul><ul><ul><li>Uses two 8 bit bytes (16 bits) </li></ul></ul><ul><ul><li>216 = 65,536 possible combinations or characters </li></ul></ul><ul><ul><li>Supports characters for all the world’s languages </li></ul></ul><ul><ul><li>Downward-compatible with ASCII </li></ul></ul>
  26. 26. The System Unit The Black Box <ul><li>Houses electronic components </li></ul><ul><ul><li>Motherboard </li></ul></ul><ul><ul><li>Storage devices </li></ul></ul><ul><ul><li>Connections </li></ul></ul><ul><li>Some Apple Macintosh models have system unit inside monitor </li></ul>
  27. 27. The System Unit The Black Box <ul><li>Motherboard </li></ul><ul><li>Microprocessor chip </li></ul><ul><li>Memory chips </li></ul><ul><li>Connections to other parts of the hardware </li></ul><ul><li>Additional chips may be added – math coprocessor </li></ul>
  28. 28. The System Unit The Black Box <ul><li>Storage Devices </li></ul><ul><li>Hard drive </li></ul><ul><li>Floppy drive </li></ul><ul><li>CD-ROM drive </li></ul><ul><li>DVD-ROM drive </li></ul>
  29. 29. Microprocessor <ul><li>CPU etched on a chip </li></ul><ul><li>Chip size is ¼ x ¼ inch </li></ul><ul><li>Composed of silicon </li></ul><ul><li>Contains millions of transistors </li></ul><ul><ul><li>Electronic switches that can allow current to pass through </li></ul></ul>
  30. 30. Microprocessor Components <ul><li>Control Unit – CU </li></ul><ul><li>Arithmetic / Logic Unit – ALU </li></ul><ul><li>Registers </li></ul><ul><li>System clock </li></ul>
  31. 31. Building a Better Microprocessor <ul><li>Computers imprint circuitry onto microchips </li></ul><ul><ul><li>Cheaper </li></ul></ul><ul><ul><li>Faster </li></ul></ul><ul><li>Perform functions of other hardware </li></ul><ul><ul><li>Math coprocessor is now part of microprocessor </li></ul></ul><ul><ul><li>Multimedia instructions are now part of microprocessor </li></ul></ul>
  32. 32. Building a Better Microprocessor <ul><li>The faster the computer runs </li></ul><ul><li>The cheaper it is to make </li></ul><ul><li>The more reliable it is </li></ul>The more functions that are combined on a microprocessor:
  33. 33. Types of Microprocessors <ul><li>Intel </li></ul><ul><li>Pentium </li></ul><ul><li>Celeron </li></ul><ul><li>Xeon and Itanium </li></ul><ul><li>Intel-compatible </li></ul><ul><li>Cyrix </li></ul><ul><li>AMD </li></ul>
  34. 34. Types of Microprocessors <ul><li>PowerPC </li></ul><ul><ul><li>Cooperative efforts of Apple, IBM, and Motorola </li></ul></ul><ul><ul><li>Used in Apple Macintosh family of PCs </li></ul></ul><ul><ul><li>Found in servers and embedded systems </li></ul></ul><ul><li>Alpha </li></ul><ul><ul><li>Manufactured by Compaq </li></ul></ul><ul><ul><li>High-end servers and workstations </li></ul></ul>
  35. 35. Semiconductor Memory <ul><li>Reliable </li></ul><ul><li>Compact </li></ul><ul><li>Low cost </li></ul><ul><li>Low power usage </li></ul><ul><li>Mass-produced economically </li></ul><ul><li>Volatile </li></ul><ul><li>Monolithic </li></ul><ul><ul><li>All circuits together constitute an inseparable unit of storage </li></ul></ul>
  36. 36. Semiconductor Memory CMOS <ul><li>Complementary metal oxide semiconductor </li></ul><ul><li>Uses little electricity </li></ul><ul><li>Used in PC to store hardware settings that are needed to boot the computer </li></ul><ul><li>Retains information with current from battery </li></ul>
  37. 37. RAM <ul><li>Keeps the instructions and data for current program </li></ul><ul><li>Data in memory can be accessed randomly </li></ul><ul><li>Easy and speedy access </li></ul><ul><li>Volatile </li></ul><ul><li>Erased </li></ul><ul><li>Written over </li></ul>
  38. 38. Types of RAM <ul><li>SRAM </li></ul><ul><li>Retains contents as long as power is maintained </li></ul><ul><li>Faster than DRAM </li></ul>
  39. 39. Types of RAM <ul><li>DRAM </li></ul><ul><li>Must be constantly refreshed </li></ul><ul><li>Used for most PC memory because of size and cost </li></ul><ul><li>SDRAM </li></ul><ul><ul><li>faster type of DRAM </li></ul></ul><ul><li>Rambus DRAM </li></ul><ul><ul><li>Faster than SDRAM </li></ul></ul><ul><ul><li>Expensive </li></ul></ul>
  40. 40. Adding RAM <ul><li>Purchase memory modules that are packaged on circuit boards </li></ul><ul><li>SIMMS – Chips on one side </li></ul><ul><li>DIMMS – Chips on both sides </li></ul><ul><li>Maximum amount of RAM that can be installed is based upon the motherboard design </li></ul>
  41. 41. ROM <ul><li>Programs and data that are permanently recorded at the factory </li></ul><ul><li>Read </li></ul><ul><li>Use </li></ul><ul><li>Cannot be changed by the user </li></ul><ul><li>Stores boot routine that is activated when computer is turned on </li></ul><ul><li>Nonvolatile </li></ul>
  42. 42. PROM <ul><li>Programmable ROM </li></ul><ul><li>ROM burner can change instructions on some ROM chips </li></ul>
  43. 43. Bus Line <ul><li>Paths that transport electrical signals </li></ul><ul><li>System bus </li></ul><ul><ul><li>Transports data between the CPU and memory </li></ul></ul><ul><li>Bus width </li></ul><ul><ul><li>Number of bits of data that can be carried at a time </li></ul></ul><ul><ul><li>Normally the same as the CPUs word size </li></ul></ul><ul><li>Speed measured in MHz </li></ul>
  44. 44. Bus Line <ul><li>CPU can support a greater number and variety of instructions </li></ul>More memory available = CPU can reference larger memory addresses Faster computer = CPU can transfer more data at a time More powerful computer = Larger bus width
  45. 45. Expansion Buses <ul><li>Connect the motherboard to expansion slots </li></ul><ul><li>Plug expansion boards into slots </li></ul><ul><ul><li>interface cards </li></ul></ul><ul><ul><li>adapter cards </li></ul></ul><ul><li>Provides for external connectors / ports </li></ul><ul><ul><li>Serial </li></ul></ul><ul><ul><li>Parallel </li></ul></ul>
  46. 46. Expansion Buses
  47. 47. PC Buses and Ports Credit card sized PC card devices normally found on laptops PC Card High-speed bus connecting video equipment to the computer IEEE 1394 (FireWire) Supports “daisy-chaining” eliminating the need for multiple expansion cards; hot-swappable USB Connects memory and graphics card for faster video performance AGP High-speed devices like hard disks and network cards PCI Slow-speed devices like mouse, modem ISA
  48. 48. Speed and Power <ul><li>What makes a computer fast? </li></ul><ul><li>Microprocessor speed </li></ul><ul><li>Bus line size </li></ul><ul><li>Availability of cache </li></ul><ul><li>Flash memory </li></ul><ul><li>RISC computers </li></ul><ul><li>Parallel processing </li></ul>
  49. 49. Computer Processing Speed <ul><li>Time to execute an instruction </li></ul><ul><li>Millisecond </li></ul><ul><li>Microsecond </li></ul><ul><li>Nanosecond </li></ul><ul><ul><li>Modern computers </li></ul></ul><ul><li>Picosecond </li></ul><ul><ul><li>In the future </li></ul></ul>
  50. 50. Microprocessor Speed <ul><li>Clock speed </li></ul><ul><ul><li>Megahertz (MHz) </li></ul></ul><ul><ul><li>Gigahertz (GHz) </li></ul></ul><ul><li>Number of instructions per second </li></ul><ul><ul><li>Millions of Instructions Per Second (MIPS) </li></ul></ul><ul><li>Performance of complex mathematical operations </li></ul><ul><ul><li>One million floating-point operations per second (Megaflop ) </li></ul></ul>
  51. 51. Cache <ul><li>Small block of very fast temporary memory </li></ul><ul><li>Speed up data transfer </li></ul><ul><li>Instructions and data used most frequently or most recently </li></ul>
  52. 52. Cache Step 1 Processor requests data or instructions <ul><ul><li>Step 2 </li></ul></ul><ul><ul><li>Go to address in main memory and read </li></ul></ul>Step 3 Transfer to main CPU and cache <ul><li>Next processor request </li></ul><ul><li>Look first at cache </li></ul><ul><li>Go to memory </li></ul>P R O C E S S O R R A M Cache
  53. 53. Types of Cache <ul><li>Internal cache </li></ul><ul><ul><li>Level 1 (L1) </li></ul></ul><ul><ul><li>Built into microprocessor </li></ul></ul><ul><ul><li>Up to 128KB </li></ul></ul><ul><li>External cache </li></ul><ul><ul><li>Level 2 (L2) </li></ul></ul><ul><ul><li>Separate chips </li></ul></ul><ul><ul><li>256KB or 512 KB </li></ul></ul><ul><ul><li>SRAM technology </li></ul></ul><ul><ul><li>Cheaper and slower than L1 </li></ul></ul><ul><ul><li>Faster and more expensive than memory </li></ul></ul>
  54. 54. Flash Memory <ul><li>Nonvolatile RAM </li></ul><ul><li>Used in </li></ul><ul><ul><li>Cellular phones </li></ul></ul><ul><ul><li>Digital cameras </li></ul></ul><ul><ul><li>Digital music recorders </li></ul></ul><ul><ul><li>PDAs </li></ul></ul>
  55. 55. Instruction Sets <ul><li>CISC Technology </li></ul><ul><ul><li>Complex Instruction Set Computing </li></ul></ul><ul><ul><li>Conventional computers </li></ul></ul><ul><ul><li>Many of the instructions are not used </li></ul></ul><ul><li>RISC Technology </li></ul><ul><ul><li>Reduced Instruction Set Computing </li></ul></ul><ul><ul><li>Small subset of instructions </li></ul></ul><ul><ul><li>Increases speed </li></ul></ul><ul><ul><li>Programs with few complex instructions </li></ul></ul><ul><ul><ul><li>Graphics </li></ul></ul></ul><ul><ul><ul><li>Engineering </li></ul></ul></ul>
  56. 56. Types of Processing <ul><li>Serial processing </li></ul><ul><ul><li>Execute one instruction at a time </li></ul></ul><ul><ul><li>Fetch, decode, execute, store </li></ul></ul><ul><li>Parallel Processing </li></ul><ul><ul><li>Multiple processors used at the same time </li></ul></ul><ul><ul><li>Can perform trillions of floating-point instructions per second (teraflops) </li></ul></ul><ul><ul><li>Ex: network servers, supercomputers </li></ul></ul>
  57. 57. Types of Processing <ul><li>Pipelining </li></ul><ul><ul><li>Instruction’s action need not be complete before the next begins </li></ul></ul><ul><ul><li>Fetch instruction 1, begin to decode and fetch instruction 2 </li></ul></ul>