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Computer Organization(CS 221) Þ Computer Organization, Computer Architecture, Differences Þ Von-Neumann Architecture Þ Register Transfer Language Þ Register Transfer Þ Bus and Memory Transfers Isha Padhy, Department of CSE, CBIT, Hyderabad 1

Computer organization

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Computer Organization

Computer Organization(CS 221)Computer Organization, Computer Architecture, DifferencesVon-Neumann ArchitectureRegister Transfer LanguageRegister TransferBus and Memory TransfersIsha Padhy, Department of CSE, CBIT, Hyderabad1

What is a computer?A computer is a genera lpurpose programmable electronic machine, having 2 principal characteristics:Responds to a specific set of coded instructions in a well defined manner.It can execute a list of instructions termed as program.What is the difference between computers in starting days and now?

Isha Padhy, Department of CSE, CBIT, Hyderabad2

How a computer perform a task?Instruction Set Architecture(ISA)Applications/AppsProgram(Java, C++)Operating System(Android, Mac OS, Windows)Micro- architecture(Implementation of ISA)Digital Logic CircuitsElectrical signalsIsha Padhy, Department of CSE, CBIT, Hyderabad3

Computer organization and architectureArchitecture describeswhatthe computer does and organization describeshowit does it.A computer'sarchitectureis its abstract model and is the programmer's view in terms of instructions, addressing modes and registers. A computer'sorganisationexpresses the realization of the architecture.Architecture and organisation are independent; you can change the organisation of a computer without changing its architecture.Computer organizationDescribes the function and the way computer components are operated and the way they are connected together to form the computer system.Computer architecture - the structure and behavior of computer as seen by the user. - instruction formats, the instruction set and techniques for addressing memory.

Isha Padhy, Department of CSE, CBIT, Hyderabad4

Some questionsWhy has the speed of computer performance increased so much since 1970?Is the gear lever in a car part of its architecture or organization?Can u change the organization without changing the architecture?

Isha Padhy, Department of CSE, CBIT, Hyderabad5

Von Neumann architectureThevon Neumann architecture, which is also known as thevon Neumann modelandPrinceton architecture, is acomputer architecturebased on that described in 1945 by the mathematician and physicistJohn von Neumann.AvonNeumannmachinehas:-A Central processing Unit(CPU)withone ormoreregistersthatholddatathatarebeingoperatedon.TheCPUcaninterpretthecontentsofmemoryeitherasinstructionsoras dataaccordingtothefetch-execute cycle.Execution occurs in a sequential fashion from one instruction to the next, unless explicitly modified.Random Access Memory(RAM)whichmeansthateach successiveoperationcanreadorwriteanymemorylocation,independentof thelocationaccessedbythepreviousoperation.The contents of this memory are addressable by location without regarding to the type of data contained there.Control unit, which interprets and executes the instructions in memory.Input/Outputunit, operated by the control unit.

Isha Padhy, Department of CSE, CBIT, Hyderabad6

Isha Padhy, Department of CSE, CBIT, Hyderabad7

Registers in CPU

Isha Padhy, Department of CSE, CBIT, Hyderabad8- The registers are temporary storage locations to quickly store and transfer the data and instructions being used. - As the registers are often on the same chip and directly connected to the CU, the registers have faster access time than memory. Therefore, using registers both as the source of operands and as the destination of results will improve the performance.

Memory unitThe function of the memory is to store programs and data.There are two classes of storage, called primary and secondary.- Primary storage is a fast memory that operates at electronic speeds. Programs must stay in memory while they are being executed. The memory contains a large number of semiconductor storage cells, each capable of storing one bit of information.Random access memory: Memory in which any location can be reached in a short and fixed amount of time after specifying its address is called random access memory (RAM).- Secondary storage:Although primary storage is essential, it tends to be expensive.Thus additional, cheaper, secondary storage is used when large amounts of data and many programs have to be stored, particularly for information that is accessed infrequently. A wide selection of secondary storage devices is available, including magnetic disks,tapes and optical disks (CD-ROMs)Isha Padhy, Department of CSE, CBIT, Hyderabad9

Isha Padhy, Department of CSE, CBIT, Hyderabad10

In a computer, theMemory Address Register(MAR) is the CPUregisterthat either stores thememory addressfrom which data will be fetched to the CPU or the addressto which data will be sent and stored.The MAR can hold two different kinds of addresses. Either it stores the address of an instruction, or it stores the address of data.This register has its output hooked up to the address bus.TheMemory Data Register(MDR) orMemoryBufferRegister(MBR) is the registerof a computer's control unit that contains thedatato be stored in the computer storage (e.g. RAM), or thedataafter a fetch from the computer storage.It is used with the data busIsha Padhy, Department of CSE, CBIT, Hyderabad11

Arithmetic and logic unit (ALU)Most computer operations are executed in the arithmetic and logic unit (ALU) of the processor.Performs arithmetic operations(+,-,/,*) and logical operations(AND,OR,NOT)

For example, Suppose two numbers are to be added. They are brought into the processor, and the actual addition is carried out by the ALU.

The sum may then be stored in the memory or retained in the processor for immediate use.

When operands are brought into the processor, they are stored in high-speed storage elements called registers.Isha Padhy, Department of CSE, CBIT, Hyderabad12

Control Unit

Isha Padhy, Department of CSE, CBIT, Hyderabad

Control unit determines the order in which instructions should be executed and controls the retrieval of the proper operands. It interprets the instructions of the machine.


MARMDR500LDA 700501ADD 701502STO 702...7002770135

500LDA 70027500LDA 700Isha Padhy, Department of CSE, CBIT, Hyderabad14123455

Complete Figure

Isha Padhy, Department of CSE, CBIT, Hyderabad15

Register Transfer LanguageThe hardware organization of a digital computer is defined by specifying: The set of register it contains and their function.The sequence of micro- operations performed on the binary information stored in the registers.The control that initiates the sequence of micro-operations

A computer system is made of different digital modules which are designed using registers, decoders, control logics.Every module has a set of registers and some operations are done on data in these registers. RTL is the symbolic notation used to describe the micro-operation transfers among registers.Micro-operations are elementary operations performed on the information stored in one or more registers.An instruction is fetched from memory, decoded and executed by performing a sequence of micro-operations.The micro-operations only specify which data transfers may occur , they dont specify when or how they may occur.

Isha Padhy, Department of CSE, CBIT, Hyderabad16

Register TransferRegisters are denoted by capital letters and are sometimes followed by numeralsRegister are notated by a name of choice. Ex A, R3 or pre-described names like PC, MAR.The most sig. bit of an n-bit register is bit n-1; the least sig. is bit 0.Copying all the contents of one register to another is a register transfer.Indicated as R2r1.All RTL instruction take one clock cycle to complete. Isha Padhy, Department of CSE, CBIT, Hyderabad17


Isha Padhy, Department of CSE, CBIT, Hyderabad18R101011101












Isha Padhy, Department of CSE, CBIT, Hyderabad19

RTL symbols

Isha Padhy, Department of CSE, CBIT, Hyderabad20SymbolDescriptionExamplesAlpha-numericsRegister NamesMAR, R2,AParentheses()Portions of registersR3(0-7),R1(L), MBR(8-15)Arrow