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BASIC COMPUTER ARCHITECTURE THE REGISTER ARRAY

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					BASIC COMPUTER ARCHITECTURE


   HOW COMPUTER SYSTEMS WORK
                    A SIMPLE COMPUTER ARCHITECTURE
                   PC                            CONTROL UNIT         MAIN MEMORY
REGISTERS
                                  +1




                          IR
                                                    CONTROL SIGNALS

                                                          MBR


                               LATCH



            ALU                CONTROL SIGNALS




                                                 BUS 1



                  BUS 3                                  MAR
                          BASIC COMPUTER ARCHITECTURE
                                   THE REGISTER ARRAY



   All modern CPU’s have an array of registers
        usually at least 32 general purpose registers
        frequently some so-called gp registers have dedicated use
   Characteristics of registers
        usually contain one computer word
        can be accessed in one CPU cycle
   Functions of registers
        serve as source of operands
        serve as destination of results
        temporarily store intermediate results
        serve as index registers to access arrays
   Specialized registers
        floating point registers
        store constants ….frequently used values
                       BASIC COMPUTER ARCHITECTURE
                                  THE REGISTER ARRAY



   Other specialized registers
        program counter
        stack pointer
        frame pointer
        base register
        instruction register
        memory address register
        memory buffer register
        some systems use “general purpose” registers to perform some of
         these functions
   Consequences of the use of registers
        faster program execution
        shorter instruction formats
        address mode flexibility
                      BASIC COMPUTER ARCHITECTURE
                             THE PROGRAM COUNTER



   The program counter…..PC
       stores address of next instruction to execute
       must be incremented after each instruction
       may be changed by function call or jump
       controls flow of program execution
                       BASIC COMPUTER ARCHITECTURE
                            THE INSTRUCTION REGISTER



   The instruction register contains the currently executing instruction
        holds instruction while it is being decoded
        opcode field provides input to control system indicating operation to
         perform
        contains addresses of operands to be used in operation
        contains destination address of result
        contains information about addressing modes to be used
                      BASIC COMPUTER ARCHITECTURE
                          THE ARITHMETIC/LOGIC UNIT



   The arithmetic/logic unit….. ALU
       performs arithmetic and logical functions
       add, subtract, multiply, divide, complement, shift…etc.
       function performed is determined by the control signals received
       will have input and output latches to hold operands and results
                       BASIC COMPUTER ARCHITECTURE
                          THE MEMORY ADDRESS REGISTER



   The memory address register      MAR
        holds address of the location in memory to be accessed
        this may be the address of the next instruction to be fetched
        may be the address of an operand to be read from memory
        may be the address of information to be written to memory
                      BASIC COMPUTER ARCHITECTURE
                        THE MEMORY BUFFER REGISTER



   The memory buffer register      MBR
       holds values to be transferred between main memory and the CPU
       data or instructions read from memory
       values to be written to memory
       most modern machines are capable of transferring more than a single
        word
                          BASIC COMPUTER ARCHITECTURE
                                    THE CONTROL UNIT



   Control Unit
        provides control signals necessary to control the hardware of the CPU
        may be hardwired
             signals are generated by a combinational logic circuit
             faster
             less flexible
             harder to design and debug
        may be microprogrammed
             signals are stored in control memory
             slower than hardwired
             more flexible
             easier to design and debug
        control signals are needed to control functions of various hardware
         units and to direct the flow of information within the CPU
                         BASIC COMPUTER ARCHITECTURE
                                  THE MEMORY UNIT



   Main Memory
       used to store programs and data
       volatile
       usually uses DRAM…dynamic random access memory
            slower than static ram
            must be refreshed
            requires fewer transistors to implement
            improves packing density on IC…allowing larger, cheaper memories
       most memory is byte addressable
            retrieve a single byte per memory access
       can be organized to access a full word or even multiple words per
        access
       cache memory is a distinct memory positioned between the CPU and
        MM
            faster
            smaller
            more expensive
                         BASIC COMPUTER ARCHITECTURE
                                  THE BUS STRUCTURE



   CPU bus structure
       a bus is an “information path” connecting the various functional units
        within the CPU
       generally will be capable of transmitting one entire word in parallel
            will consist of one word length of “wires” or data paths
       the CPU will have multiple buses to improve the information transfer
        options within the CPU to maximize the flexibility and parallelism of
        the system

				
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posted:9/28/2012
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