prelims coe elec2

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Computer Systems Organization and Architecture

- A Review -

Miss Sheena I. Sapuay

Instructor, CoE Elec 2



ARCHITECTURE

± A general term referring to the structure of all or

part of a computer system.

± The term also covers the design of system

software, such as the operating system (the

program that controls the computer), as well as

referring to the combination of hardware and

basic software that links the machines on a

computer network.

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ARCHITECTURE cont.

Computer architecture refers to an entire structure and

to the details needed to make it functional.

Thus, computer architecture covers computer systems,

microprocessors, circuits, and system programs.

the term does not refer to application programs, such as

spreadsheets or word processing, which are required to

perform a task but not to make the system run.

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COMPUTER

Machine that performs tasks, such as

calculations or electronic communication,

under the control of a set of instructions

called a program.

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USES OF COMPUTER

In business, computers track inventories with bar codes

and scanners, check the credit status of customers, and

transfer funds electronically.

In homes, tiny computers embedded in the electroniccircuitry of most appliances control the indoor

temperature, operate home security systems, tell the

time, and turn videocassette recorders (VCRs) on and off.

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USES OF COMPUTER cont.

Computers in automobiles regulate the flow of fuel,

thereby increasing gas mileage.

Computers also entertain, creating digitized sound on

stereo systems or computer-animated features from adigitally encoded laser disc.

Educators use computers to track grades and

communicate with students (computer aided

instruction).

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Computers are used extensively in scientific

research to solve mathematical problems,

investigate complicated data, or model

systems that are too costly or impractical to

build, such as testing the air flow around the

next generation of aircraft.

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The military employs computers in

sophisticated communications to encode and

unscramble messages, and to keep track of

personnel and supplies.

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BASIC COMPUTER ORGANIZATION

The physical computer and its components are known ashardware.

Computer hardware includes: ± the memory that stores data and program instructions;

± the central processing unit (CPU) that carries out program instructions;

± the input devices, such as a keyboard or mouse, that allow the user tocommunicate with the computer;

± the output devices, such as printers and video display monitors, thatenable the computer to present information to the user;

± buses (hardware lines or wires) that connect these and other computercomponents.

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BASIC COMPUTER ORGANIZATION

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STORED PROGRAM ARCHITECTURE

one that keeps its programmed instructions,

as well as its data, in read-write, random-

access memory (RAM)

This architecture is implemented using Von

Neumann Architecture

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VON NEUMANN ARCHITECTURE

a design model for a stored-program digital

computer that uses a central processing unit

(CPU) and a single separate storage structure

("memory") to hold both instructions and

data.

It is named after the mathematician and early

computer scientist John von Neumann.

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All temporary computer designs are based on

this architecture

KEY CONCEPTS: ± Data & instructions are stored in a single read-

write memory

± Contents of memory are addressable by location

± Execution occurs in a sequential fashion

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VON NEUMANN BOTTLENECK

separation between the CPU and memory

± the limited throughput (data transfer rate)

between the CPU and memory compared to the

amount of memory

seriously limits the effective processing speed

when the CPU is required to perform minimal

processing on large amounts of data

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VON NEUMANN BOTTLENECK

The CPU is continuously forced to wait for

needed data to be transferred to or from

memory.

Since CPU speed and memory size have

increased much faster than the throughput

between them, the bottleneck has become

more of a problem, a problem whose severityincreases with every newer generation of CPU.

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CENTRAL PROCESSING UNIT

Otherwise known as processor

the portion of a computer system that carries

out the instructions of a computer program,and is the primary element carrying out the

computer's functions

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ACTIONS PERFORMED BY CPU

Processor Memory

± Data may be transferred from processor to

memory & vice versa

Processor I/O

± Data may be transferred to or from a peripheral

device by transferring bet. the processor and anI/O module




INSTRUCTION PROCESSING

Processor reads (fetch) instruction from

memory one at a time & executes each

instruction

PROGRAM EXECUTION:

± F ETCH CYCLE instruction & data is taken from

the memory

± EXECUTE CYCLE instruction is executed by the

processor




INSTRUCTION CYCLE

also called fetch-and-execute cycle or fetch-

decode-execute cycle

the time period during which a computerprocesses a machine language instruction

from its memory or the sequence of actions

that the central processing unit (CPU)

performs to execute each machine codeinstruction in a program




Basic Instruction Cycle




INSTRUCTION CYCLE

Fetch the instruction

± The CPU presents the value of the program

counter (PC) on the address bus.

± The CPU then fetches the instruction from main

memory via the data bus into the memory data

register (MDR).

±The value from the MDR is then placed into theinstruction register (IR).




INSTRUCTION CYCLE

Decode the instruction

± The instruction decoder interprets and

implements the instruction.

± The instruction register (IR) holds the current

instruction, while the program counter (PC) holds

the address in memory of the next instruction to

be executed. ± Fetch required data from main memory to be

processed and place it into data registers.




INSTRUCTION CYCLE

Execute the instruction

From the instruction register, the data forming theinstruction is decoded by the control unit.

It then passes the decoded information as asequence of control signals to the relevant functionunits of the CPU to perform the actions required bythe instruction such as reading values from

registers, passing them to the Arithmetic logic unit(ALU) to add them together and writing the resultback to a register.




PROGRAM COUNTER (PC)

Holds the address of the instruction to fetched

next

Unless told otherwise, the processor always

increment the PC after each instruction is fetched

EX. PC=300,

± The processor will the next instruction at location 300

±After fetching, PC is incremented the next value of PCis 301, then 302, 303, and so on.




INSTRUCTION REGISTER (IR)

Register inside the CPU where the fetched

instruction is loaded

a circuit that holds the instruction temporarilyso that it can be decoded and executed

INSTRUCTION

± Bits specifying the action of the processor to take




ILLUSTRATIVE EXAMPLE




Example of Program Execution(contents of memory and registers in hexadecimal)




INTERRUPTS & INSTRUCTION CYCLE

The processor can be engaged in executing

other instructions while an I/O operation is in

progress

An interruption of the normal sequence of

program execution

Execution resumes when interrupt processing

is completed




INTERRUPTS

Interrupt the normal sequencing of the

processor

Provided to improve processor utilization ± Most I/O devices are slower than the processor

± Processor must pause to wait for device




Transfer Control via Interrupt




CLASSES OF INTERRUPTS




INSTRUCTION CYCLE W/ & W/O INTERRUPTS




Instruction Cycle with Interrupts


HALT

Fetch Next

Instruction

Fetch Cycle Execute Cycle

Execute

Instruction

Check for

Interrupt;

Process

Interrupt

START

Interrupts

disabled

Interrupts

enabled

Interrupt Cycle



SIMPLE INTERRUPT PROCESSING




MULTIPLE INTERRUPT PROCESSING

Suppose an interrupt occurs while another

interrupt is being processed.

± E.g. printing data being received via

communications line.

Two approaches:

± Disable interrupts during interrupt processing

± Use a priority scheme.




THE MICROPROCESSOR

An electronic circuit that functions as thecentral processing unit (CPU) of a computer,providing computational control.

one type of ultra-large-scale integrated circuit.

Integrated circuits, also known as microchips orchips, are complex electronic circuits consisting

of extremely tiny components formed on asingle, thin, flat piece of material known as asemiconductor.




THE MICROPROCESSOR

Modern microprocessors incorporate

transistors (which act as electronic amplifiers,

oscillators, or, most commonly, switches), in

addition to other components such as

resistors, diodes, capacitors, and wires, all

packed into an area about the size of a

postage stamp.




THE MICROPRESSOR: SECTIONS

Arithmetic/Logic Unit (ALU)

performs calculations on numbers and makes logical

decisions

Registers

the registers are special memory locations for storing

temporary information much as a scratch pad does

Control Unit deciphers programs; logic which controls the data

paths




THE MICROPRESSOR: SECTIONS

Buses

± carry digital information throughout the chip and

computer

Cache memory

± Internal data storage

± speed up access to external data-storage devices




THE MICROPROCESSOR

Modern microprocessors operate with buswidths of 64 bits, meaning that 64 bits of datacan be transferred at the same time.

A crystal oscillator in the computer provides aclock signal to coordinate all activities of themicroprocessor.

The clock speed of microprocessors allowsbillions of computer instructions to beexecuted every second.




MACHINE INSTRUCTION

The operation of the CPU is determined by the

instructions it executes

Each CPU comprises an INSTRUCTION SET

± Collection of instructions that the CPU executes




ELEMENTS OF MACHINE INSTRUCTION

Each instruction must contain the information

required by the CPU for execution

OPERATION CODE specifies the operation to

be performed (ADD, MOV etc.), specified by a

binary code




ELEMENTS OF MACHINE INSTRUCTION

SOURCE OPERAND

± Operands that are input for the operation

RESULT OPERAND ± Operation may produce result

NEXT INSTRUCTION REFERENCE

± Tells the CPU where to fetch the next instruction.




INSTRUCTION REPRESENTATION

Each instruction is represented by a sequenceof bits

Ex.

OPCODES are represented by abbreviations calledmnemonics that indicate operations


OP CODE OPERAND REF OPERAND REF

4 bits 6 bits 6 bits

16 bits



INSTRUCTION TYPES

A high-level language expresses operation in a

concise algebraic form using variables

A machine language expresses operation in a

basic form involving movement of data to or

from registers




INSTRUCTION TYPES

Data Processing

± Arithmetic/logic instructions

Data Storage ± Memory instructions

Data Movement

± I/O instructions

Control

± Test and branch instructions




TYPES OF OPERANDS

Addresses

Numbers

±

Numeric data types (integer, float, decimal) Characters

± Text or character strings

Logical Data ± Boolean data




INSTRUCTION SET

a list of all the instructions, and all theirvariations, that a processor can execute

Instructions include:

Arithmetic such as add and subtract

Logic instructions such as and, or, and not

Data instructions such as move, input, output, load,

and store Control flow instructions such as goto, if ... goto, call,

and return.




INSTRUCTION SET ARCHITECTURE (ISA)

is the part of the computer architecture related

to programming, including the native data types,

instructions, registers, addressing modes,memory architecture, interrupt and exception

handling, and external I/O

An ISA includes a specification of the set of

OPCODES, the native commands implemented

by a particular processor.




CISC

stands for Complex Instruction Set Computer

Most PC's use CPU based on this architecture

Typically CISC chips have a large amount of different and complex instructions.




CISC

The philosophy behind this is hardware is

always faster than software, therefore one

should make a powerful instruction set, which

provides programmers with assembly

instructions to do a lot with short programs.




RISC

stands for Reduced Instruction Set Computer.

The philosophy behind it is that almost no one

uses complex assembly language instructions

as used by CISC, and people mostly use

compilers which never use complex

instructions.




RISC

fewer, simpler and faster instructions would be

better, than the large, complex and slower CISC

instructions. However, more instructions are needed to

accomplish a task.

because of the more simple instructions, RISCchips require fewer transistors, which makes

them easier to design and cheaper to produce




CISC versus RISC


CISC RISC

Emphasis on hardware Emphasis on software

Includes multi-clockcomplex instructions

Single-clock,reduced instructiononly

Memory-to-memory:"LOAD" and "STORE"incorporated ininstructions

Register to register:"LOAD" and "STORE"are independentinstructions

Small code sizes,high cycles per

second

Low cycles per second,

large code sizes

Transistors used forstoringcomplex instructions

Spends more transistorson memory registers



Decades of Computing

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