Computer Architecture & Organization

Von Neumann Architecture 1Philip Jayson Cortez

Von Neumann Architecture

Objectives1. To define the basic components of a

Computer System2. To define the functions of Various

Components of a Computer3. To define the basic hardware

terminology

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The Stored Program Computer1943: ENIAC

Presper Eckert and John Mauchly -- first general electronic computer.Hard-wired program -- settings of dials and switches.

1944: Beginnings of EDVACamong other improvements, includes program stored in memory

1945: John von Neumannwrote a report on the stored program concept, known as the First Draft of a Report on EDVAC

The basic structure proposed in the draft became knownas the “von Neumann machine” (or model).

a memory, containing instructions and dataa processing unit, for performing arithmetic and logical operationsa control unit, for interpreting instructions

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What is a Computer?

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A general purpose programmable electronic machine having two principal characteristics:1. Responds to a specific set of coded instruction in a well-defined manner2. It can execute a pre-recorded list of instructions termed as Program

Von Neumann Architecture Philip Jayson Cortez

What is a Program?

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Basically a Set of

Instructions

Von Neumann Architecture Philip Jayson Cortez

What is an Instruction?

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A Binary Coded Command Designed for a specific task:

- Arithmetic and Logic Instructions- Looping and Decision Making- Transfer of Data- Transfer of Control

Execution of Instruction

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1. Get the instruction2. Decode the instruction3. Get the Operands4. Perform the desired operation5. Communicate the results back

Instruction Codes

Instruction Interpreter

Control Signals

Instruction ProcessorData

Result

Need of Memory

Von Neumann Architecture Philip Jayson Cortez

- Non-Linear Programming Paradigm

- An operation on data may require more than one data value in a predetermined sequence

- Speed of Input vs the Speed of Processing Unit

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Key Concepts:

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von Neumann Machine

- Data and Instructions in a Single Read-Write Memory

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Key Concepts:

von Neumann Machine

-the contents of the memory addressable by location irrespective of the type of data stored

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Key Concepts:

von Neumann Machine

-Sequential execution of Instruction unless explicitly modified by instruction

Von Neumann Architecture Philip Jayson Cortez

General Computer Structure

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1. Main Memory : for storing data and instruction

2. Central Processing Unit : - Arithmetic-Logic Unit (ALU)- Control Unit (CU)- Operational Registers

3. Input / Output System

Von Neumann Architecture Philip Jayson Cortez

Design of the von Neumann Architecture

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CPU Structure

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Arithmetic Logic Unit

Instruction Decoder

IR MAR PSW

MBR PC

MM

I/O

SYSTEM BUS

DR

AC MQ

Legend:

CONTROL UNIT:MAR: memory address registerIR: instruction registerMBR : memory buffer registerPSW: program status word

ALU UNIT:AC: accumulator registerDR: general purpose registerMQ: multiplier-quotient register

MM : Main Memory

Control Unit

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- coordinates and controls all hardware

- accomplished by using the contents of the instruction register to decide which circuits are to be activated

- responsible for fetching instructions from the main memory and decoding the instruction

Von Neumann Architecture Philip Jayson Cortez

Control Unit - directs the entire computer system to carry out

stored program instructions - must communicate with both the arithmetic logic unit

and main memory - uses the instruction contained in the Instruction Register

to decide which circuits need to be activated.

- instructs the arithmetic logic unit which arithmetic operations or logical operation is to be performed.

- the control unit is literally in control.

Control Unit

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MAR: memory address register

- a register located on the processing unit, w/c in turn, connected to the address lines of the system

- specifies the address in memory where information can be found- also used to point a memory location where information is to be stored

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Control Unit

IR: instruction register

- holds the contents of the last instruction fetched

- this instruction is now ready to be executed

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Control Unit

MBR: memory buffer register

- main purpose of this register is to act as an interface between the central processing unit and memory

- when the CU receives the appropriate signal, the memory location stored in the MAR is used to copy data from or to the memory buffer register

Von Neumann Architecture Philip Jayson Cortez

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Control Unit

PC: program counter

-contains the memory address of the next instruction to be executed

-contents of the PC are copied to the MAR before an instruction is fetched from memory

-at the completion of the fetched instruction, the CU updates the PC to point to the next instruction w/c is to be fetched

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Control Unit

PSW: program status word

- referred to as Status Register (SR)

- contains key information used by CPU to record exceptional conditions

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Arithmetic Logic Unit (ALU)

Von Neumann Architecture Philip Jayson Cortez

-executes arithmetic and logical operations- Arithmetic operations include addition, subtration,

multiplication and division. -Logical operations compare numbers, letters and special characters- Comparison operations test for three conditions: 

1. equal-to condition in which two values are the same 2. less-than condition in which one value is smaller than the other 3. greater-than condition in which one value is larger than the other

- Relational operations (=, <, >) are used to describe the comparison operations used by the arithmetic logic unit.

-The arithmetic logic unit performs logic functions such as AND, OR and NOT.

Arithmetic Logic Unit

AC : accumulator- is used to accumulate results. - it is the place where the answers from many operations

are stored temporarily before being put out to the computer's memory.

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Arithmetic Logic Unit

DR : general-purpose register

-hold data on which operations are to be performed by the arithmetic logic unit.

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Registers

- the smallest units of memory and are located internally w/in the CPU

- most often used to either temporarily store results or control information

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Registers

Two Basic functions:

1. User-Visible Registers-enables machines/assembly language programs to

minimize memory references

2. Control and Status Registers

- control the execution of programs

Von Neumann Architecture Philip Jayson Cortez

ReferencesCS212 Computer Architecture, Study Guidewww.geocites.com/cflerihttp://www.youtube.com/user/ignousocis

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