Overview of Computer Architecture and Organization Module I Overview of Computer Architecture and Organization

Structure of IAS Computer

UQ: Explain the role of different registers like IR,PC,SP,AC,MAR,MDR used in Von Neumann Model [5]

Functions of different registers Memory Buffer Register (MBR) (Data Register) Store any 40-bit word Used to store operand of an instruction It contains a word to be stored in memory or sent to I/O unit or it is used to receive a word from memory or I/O unit

Functions of different registers Memory Address Register(MAR)/ Address Register(AR) 12 bit register Specify the address of the memory location to be written into or read from MBR

Functions of different registers Instruction Register(IR) Holds the opcode of currently executing instruction Instruction Buffer Register(IBR) Since 2 instructions are fetched simultaneously, the opcode of the second instruction is stored in IBR Program Counter(PC) Store address of the next instruction pair to be executed Also referred as Instruction Address Register

Functions of different registers Accumulator (AC) and Multiplier Quotient (MQ) 40 bit register Used for the temporary storage of operands and results of the ALU operation E.g. result of multiplication of two 40 bit numbers are stored as Most Significant : AC Least Significant : MQ

Instruction Cycle of IAS It consist Fetch Cycle Execute Cycle

Fetch Cycle Opcode of next instruction is loaded into IR and address portion into MAR This instruction may be taken from IBR or loaded from memory by loading a word into the MBR and then down to IBR,IR and MAR.

Execute Cycle Once opcode reaches IR execution begins Control circuitry interprets opcode and executes instruction using control signals and ALU

Quiz Which is not a function of computer ? Data Processing Data Packing Data Storage Data Movement

Quiz Which is not a structural component of computer ? CPU Main Memory Operating System System Interconnections

Quiz Which is the first type of Programming Language ? Assembly Level Machine Level High Level

Quiz ENIAC stands for Electronic Numeric Integrator and Computer Electronic Numeric Integrator and Calculator Electric Numeric Integrator and Computer Electric Numeric Integrator and Calculator

Performance Measurements

Clock Speed Operations of Processor is governed by System clock Speed of the processor is dictated by pulse frequency of clock Clock signals are generated by a quartz crystal which generates a constant signal wave when power is applied. This wave is converted to digital voltage and is given to processor

Clock Speed Rate of pulses is clock rate or clock speed One increment of clock is clock cycle Time between pulses is cycle time Multiple instructions may get executed simultaneously, hence clock speed alone cannot define performance