Internal hardware and external components of a computer Three-box Model Processor The brain of the system Executes programs A big finite state machine.

Internal hardware and external components of a computer

Three-box Model

Processor• The brain of the system• Executes programs• A big finite state machine• Typical processor contains 100,000,000 transistors• Moore’s law – number of components integrated into a single chip doubles

every 18-24 months

Processor Input/OutputMain Memory

Bus


Main Memory• Also known as ROM, RAM or IAS (Immediate access store)• Mainly used to store program instructions and data• Available in memory chips able to store 512k. • Integrated onto bigger boards to store up to 4gig in 32bit computers• ROM – Read only memory• RAM – Random Access Memory• EEPROM – Electrically erasable programmable read only memory

Bus• The three areas are connected by a set of parallel wires• These wires pass signals between the components.• There are 3 types of bus

• Data – a bidirectional bus, typically consisting of 32 wires used to transport data between components

• Address – a unidirectional bus, typically consisting of 32 wires used to address memory and I/O locations.

• Control – a bidirectional bus, typically consisting of 8 wires , used to transport control signals between the components.


Input / Output (I/O)• Commonly known as peripherals.

Processor

Keyboard

Main memory

KeyboardInput

Controller

VDU Output Controller

Visual Display Unit

(Disk) I/O Controller

Secondary Store

Data and AddressBuses

Control Bus


Peripherals•A computer device that is not part of the CPU.•The system bus is not connected directly to I/O devices but via an I/O controller• The I/O controller is connected to the I/O device

I/O Controller• The controller is an electronic circuit consisting of three parts

1) Electronics that interface the controller to the system bus2) A set of data, command and status registers3) Electronics appropriate for sending control signals to the device connected

to the computer

Secondary StorageThis is a permanent storage memory that is a peripheral to the CPU e.g. A hard disk.

Functional Characteristics of a processor.

A processor controls the system bus Performs operations on data by executing program instructions Program instructions are stored in main memory and are “Fetched” by the Processor Only one operation can be carried out at one time for each processor. A large part of the traffic on the system bus is addresses for memory locations.

Addressable MemoryMemory locations each have a unique address which the processor sends down the address bus.The processor determines over the control bus whether it needs to read or write to that memory location. The processor uses the data bus to then transfer any data back and fore.


Stored program concept Proposed by John von Neumann and Alan Turing A program must be resident in main memory to be executed machine code instructions are fetched, one after another, from main memory in sequence and are executed, one at a time in the processor.

Von Neumann stored program computer A serial machine Instructions are fetched one after anaother Single memory shared between program instructions and data. Data and instructions travel along a shared data bus.

Harvard stored program computer Separate instruction and data memories Separate instruction and data buses Still functions as a serial computer

Harvard Vs Von NeumannNo sharing resources with accessing data and instructions so the performance speed of a Harvard infrastructure is better.


MicrocontrollerA complete computer on a single chip. Processor, memory and I/O Used for small devices where a cheap compact system is required, e.g. Mp3 players Often use the Harvard architecture.


Structure and role of the processorA processor consists of the following components

1) Program Control Unit Fetches program instructions from memory, decodes them and executes them one a time

2) Arithmetic Logic UnitThe ALU performs arithmetic and logical operations on data such as addition and subtraction, fixed point and floating point arithmetic, Boolean logic such as AND, OR< XOR and a range of shift operations.

3) RegistersFast memory locations inside the processor that may be dedicated or general-purpose

4) Internal ClockDerived directly or indirectly from the system clock


Structure and role of the processorA processor consists of the following components

5) Internal BusesSeveral internal buses link the control unit, the ALU and the registers

6) Logic gatesUsed for flow control


General Purpose and dedicated registers

General PurposeFast memory locations used to store data temporarilyLabelled as R1, R2.....RnAccessed with instructions such as LOAD, STORE and ADD

Dedicated Registers

1) Stack Pointer (SP)Points to a stack holding return addresses, procedure or functional parameters, and local variables. It is accessed when a procedure or function is called or an interrupt is serviced.

2) Program Counter (PC)Points to the next instruction to be fetched and executed


General Purpose and dedicated registers

Dedicated Registers

3) Status RegisterHolds condition codes to indicate the outcome of operations e.g. Positive, negative, zero, interrupts enabled or overflow.

4) Accumulator (ACC)The result of the current set of calculations

5) Current Instruction register (CIR)Holds the current instruction to be executed while it is decoded and executed

6) Memory Address Register (MAR)Holds the address of the memory location currently being accessed by the processor.

7) Memory Buffer Register (MBR)Holds the data item being transferred to or from the memory location currently being accessed by the processor. Sometimes called the MDR (Memory Data Register)


System Clock and Clock Speed Timing signals that are used to regulate the rate at which instructions are executed Used to synchronise the operation of various computer components. Measured in megahertz (MHz) or gigahertz (GHz) This frequency is known as clock speed. Instructions required a set amount of clock ticks to execute. The frequency of these ticks can be increased by frequency multiplying circuits to the rate that is required by the processor. Clock ticks are provide to regulate the transfer of data, addressed and control signals along the busses at a slower rate than the processor. Clock speeds double every year.

• Intel 8088 (1990 – 4.77MHz)• 486 DX2 66 – 66Mhz (1994 est)• Pentium – Up to 300 Mhz• Pentium 4 up to 3-4 GHz• Dual Core – Up to 6GHz• Quad Core


Limits on Clock Speed

A limit needs to be set on clock speed due to the heat being generated by the chip with higher frequencies. This is why modern computers have a fan directly on the chip itself.

This causes a deviation from Moore’s law due to the level of heat and power consumption.

To solve this problem multiple cores are now used with lower frequencies.

Multicore Processors More processors are put onto one microprocessor chip. These processors are called cores Operate at lower frequencies Multiple tasks can be implemented and processes can be split.


Word LengthComputers works with binary words which are codes for instructions, memory addresses, characters, integer numbers, colours of pixels and digitised sound samples.

The greater the word length the greater the instruction set, the larger the memory, the larger the numbers that can be used etc..

Increasing Word lengthIncreasing this allows larger operands in instructions preventing the need to spend time breaking down the operands which affects performance.

32 bit computers can have more memory than 16 bits computer as more addresses accessable.

Bus WidthThe number of wires on a bus. Each wire represent one bit of information. This affects the word length. Increasing the bus width will obviously affect the performance as more data and larger addresses can be accessed.

CPU WARS Episode 1

A day in the life of a CPU

Fetch Decode Execute

Cycle

The Players

The Control Unit

The Clock

The Status Register

The CurrentInstructionRegister (CIR)

The Interrupt Register

The Program Counter

The Memory Data Register (MDR)

The Memory AddressRegister (MAR)

The Arithmetic LogicUnit (ALU)

The Accumulator

Scene 1 – The Fetch

Hi PC. What is my next instruction?

Hi CU. This is your next instruction and where in Memory

you can find it.

Since this is an address the

MAR needs to hold its

location.

F124 AC4D


Address bus – I need you to go to the memory with

this address for my next instruction

No problem

sir!

Ah . This is the instruction from

the Memory

0110100101


There you go sir.

Thankyou CIR

Right. I can now

increment to the next

instruction

I now need to pass this

instruction onto the CIR

Scene 2 – The Decode

Right. I have my instructions – now what

do they mean?I better check my

instruction set.

Instruction Set

0000101010 – Add

0110100101 – Move

0010101010 – Subtract

1110101100 – Multiply

1100000111 - Store

Ah cool. According to this my instruction is

“MOVE”

Scene 3 – The Execute

Ok Guys. Thanks for all of you

coming. Here is what I would like

you to do…..

The End….

Tick..

Internal hardware and external components of a computer Three-box Model Processor The brain of the system Executes programs A big finite state machine.

Documents

memory bus

data bus

computer main memory

address bus

types of bus data

bidirectional bus

external components

io device io controller