The Central Processing Unit:What Goes on Inside the ComputerObjectivesThe CPUThe CPUControl Unit: CUArithmetic Logic UnitData Storage and the CPUThe CPU and MemoryRegistersMemoryMemory AddressesData RepresentationRepresenting DataBitByteWordStorage SizesExecuting ProgramsHow the CPU Executes InstructionsThe Machine CycleInstruction TimeExecution TimeMachine Cycle - ExampleSystem ClockExampleCoding SchemesASCIIEBCDICUnicodeThe System UnitMotherboardStorage DevicesMicroprocessorTransistorsTypes of ChipsMemory ComponentsSemiconductor MemoryRandom Access MemoryStatic RAMDynamic RAMRead-Only MemoryFlash MemoryThe System BusBus WidthBus SpeedExpansion BusesExpansion BoardsPortsCommon Expansion Buses and PortsComputer Processing SpeedsMicroprocessor SpeedsOther Performance MeasuresCacheMemory CacheProcessor CacheRISC TechnologyParallel Processing and PipeliningPipeliningParallel ProcessingMemory: Many NamesThe Central Processing Unit:What Goes on Inside the ComputerChapter 4January 23, 2003 2Objectives Identify the components of the central processing unit and how they work together and interact with memory Describe how program instructions are executed by the computer Explain how data is represented in the computer Describe how the computer finds instructions and data Describe the components of a microcomputer system unit’s motherboard List the measures of computer processing speed and explain the approaches that increase speedJanuary 23, 2003 3The CPUJanuary 23, 2003 4The CPU Complex set of electronic circuitry Control center Set of electronic circuitry that executes stored program instructions Two parts Control Unit (CU) Arithmetic Logic Unit (ALU)January 23, 2003 5Control Unit: CU Part of the hardware that is in-charge Directs the computer system to execute stored program instructions Must communicate with memory and ALU Sends data and instructions from secondary storage to memory as neededJanuary 23, 2003 6Arithmetic Logic Unit Executes all arithmetic and logical operations Arithmetic operations Addition, subtraction, multiplication, division Logical operations Compare numbers, letters, or special characters Tests for one of three conditions Equal-to condition Less-than condition Greater-than conditionJanuary 23, 2003 7Data Storage and the CPU Two types of storage: Primary storage (memory) Stores data temporarily CPU refers to it for both program instructions and data Secondary storage Long-term storage Stored on external medium, such as a diskJanuary 23, 2003 8The CPU and Memory CPU cannot process data from disk or input device It must first reside in memory Control unit retrieves data from disk and moves it into memory Items sent to ALU for processing Control unit sends items to ALU, then sends back to memory after processing Data and instructions held in memory until sent to an output or storage device or program is shut downJanuary 23, 2003 9RegistersSpecial-purposeHigh-speedTemporary storageLocated inside CPUInstruction registerHolds instruction currently being executedStatus RegisterHolds status of ALU operationsData registerHolds data waiting to be processedHolds results from processingJanuary 23, 2003 10Memory Also known as primary storage and main memory Often expressed as random-access memory (RAM) Not part of the CPU Holds data and instructions for processing Stores information only as long as the program is in operationJanuary 23, 2003 11Memory Addresses Each memory location has an address A unique number, much like a mailbox May contain only one instruction or piece of data When data is written back to memory, previous contents of that address are destroyed Referred to by number Programming languages use a symbolic (named) address, such as Hours or SalaryJanuary 23, 2003 12Data Representation Computers understand two things: on and off Data represented in binary form Binary (base 2) number system Contains only two digits, 0 and 1 Corresponds to two states, on and offJanuary 23, 2003 13Representing Data Bit Byte WordJanuary 23, 2003 14Bit Short for binary digit Two possible values: 0 and 1 Can never be empty Basic unit for storing data 0 means off, 1 means onJanuary 23, 2003 15Byte A group of 8 bits Each byte has 256 (28) possible values For text, stores one character Can be letter, digit, or special character Memory and storage devices measured in number of bytesJanuary 23, 2003 16Word The number of bits the CPU processes as a unit Typically a whole number of bytes The larger the word, the more powerful the computer Personal computers typically 32 or 64 bits in lengthJanuary 23, 2003 17Storage Sizes Kilobyte: 1024 (210) bytes Memory capacity of older personal computers Megabyte: roughly one million (220) bytes Personal computer memory  Portable storage devices (diskette, CD-ROM) Gigabyte: roughly one billion (230) bytes Storage devices (hard drives) Mainframe and network server memory Terabyte: roughly one trillion (240) bytes Storage devices on very large systemsJanuary 23, 2003 18Executing Programs Fetch CU gets an instruction  Decode CU decodes the instruction Execute CU notifies the appropriate part of hardware to take action Control is transferred to the appropriate part of hardware Task is performed Store  Control is returned to the CUJanuary 23, 2003 19How the CPU Executes Instructions Four steps performed for each instruction Machine cycle: the amount of time needed to execute an instruction Personal computers execute in less than one millionth of a second Supercomputers execute in less than one trillionth of a second Each CPU has its own instruction set those instructions that CPU can understand and executeJanuary 23, 2003 20The Machine Cycle The time required to retrieve, execute, and store an operation Components Instruction time Execution time System clock synchronizes operationsJanuary 23, 2003 21Instruction Time Also called I-time Control unit gets instruction from memory and puts it into a register Control unit decodes instruction and determines the memory location of needed dataJanuary 23, 2003 22Execution Time Control unit moves data from memory to registers in ALU ALU executes instruction on the data Control unit stores result of