Computer Organisation and architecture

Barcodes

printed diagrams of dark/light portions

1D vs 2D barcodes

2D barcodes = QR code (requires more processing and stores more data)

barcode readers

1. laser shines light onto barcode

2. light sensor detects intensity of light reflected back, creating a waveform with white areas reflecting more (converted to 1s) and black areas reflecting less (converted to 0s)

3. This encodes the barcode colours into binary to be used in softwares

hard disk drives

• hard disks composed of metallic disks (platters - airtight for protection + spin at 3600-12500rpm)

• disks split into tracks

• tracks split into equal sized sectors

• the actuator arm moves across the platter (read/write head) changes the magnetic polarity of the sectors to represent binary

solid state drives

• made up of semiconductors

• use programmable ROM chips using NAND flash memory cells and a controller

• stores information by trapping electrical charge to organise data into blocks stored as pages

• faster access, no moving parts

optical disks (cds, dvds)

• have a singular spiral track that starts in the centre, moving outwards

• laser reads pits (grooves) and lands that reflect light differently (detected by sensors)

• read only disks are coated for protection

• writeable disks are coated with translucent dye and use higher powered lasers

digital camera

records images digitally, converting analogue data (light waves) into binary

digital camera operation

1. shutter opens letting in light through lens

2. light is focused onto a sensor (made up of millions of transistors), converting light into electrons and recording the charge as 1s and 0s per pixel

3. Camera have filters for colours (red,green,blue)

4. picture data stored on SD card as a compressed or raw file

RFID (radio frequency identification)

small wiresless tags embedded onto items and doesn’t require line of sight

how does RFID work

1. tag contains a micrscopic chip containing data about the item, with an antennae to send/receive signals.

   1. When scanned by an RFID reader, it picks up an electromagnetic power that charges the devices enough to send the data via radio frequencies to the scanner.

Laser printer

uses electrostatic charge, lasers and toner to create mono and colour prints (faster than normal printers)

laser printer operations

1. contains a rotating drum containing chemicals that hold an electrical charge

2. as the laser beam is reflected onto the drum, it creates an image where it is discharged

3. as the drum rotates, the toner is picked up, being passed onto the paper

4. paper is heat treated to fuse the toner to the printer

5. colour printing requires different toner colours

Processor

Fetches, Decodes and Executes program instructions in order to run applications

Main memory

stores data and instructions that the processor will fetch

e.g. ram and rom

RAM

Random Access Memory - stores data and can be read to or written from

ROM

Read only memory - stores data and can be read from -> stores firmware (BIOS and boot sequence/UEFI)

Addressable memory

The concept that data and instructions are stored in memory using discrete addresses.

Buses

series of parallel wires connecting internal components

Address bus

Carries the address of memory locations where data and program instructions are stored

Increasing the width increases the range of addresses and therefore addressable memory

Data bus

Data and instructions are sent to different components on the data bus.

Increasing the width increases the volume of data that can be transferred at one time

Control bus

carries control signals that regulate the operation of the computer system (e.g. clock signal, control signals)

I/O Controllers

hardware that controls the communication of data between the processor and external hardware devices

Von Neumann Architecture

A processor where data and instructions are stored in the same memory (general purpose systems)

Harvard architecture

seperate memory locations for instructions data. (Embedded systems)

Advantages of Von Neumann

- Cheaper to develop as the control unit is easier to design

- Simpler

Modern CPUS

uses von neumann's architecture but uses havard architecture for the CPU's cache

Stored program concept

serially fetching and executing machine code instructions stored in main memory by a processor that perform arithmetic and logical operations

major components in the CPU

- arithmetic logic unit

- control unit

- registers

- clock

ALU

performs arithmetic and logic operations (maths, boolean operations)

Control unit

controls various components of the processor by sending signals and decodes instructions

Clock

- generates a timing signal at a regular frequency to synchronise communication between components and processor and rest of computer system

List all the registers

- program counter

- current instruction register

- memory address register

- memory data register

- status register

- general purpose register

program counter

holds memory address of next instruction (increments after each cycle)

current instruction register

holds instruction currently during decode/execute

memory address register

stores the address of a memory location that is to be read or written to

memory data register

holds contents of memory location that has been read from or data that is to be stored

status register

• holds flags for errors - zero flags, carry flags and overflow flags

• manages interrupts - detects interrupts and prompts the CPU to pause until the interrupt request is carried out

interrupt register

type of status register, storing details of any signals received by processor (e.g. I/O)

interrupts

a signal sent by a device/program to the processor requesting its attention

vectored interrupt mechanism (not on spec??)

handling interrupts by pointing to the first memory address of the instruction needed

fetch

1. contents of PC copied to MAR

2. MAR gets instruction from main memory through address bus

3. data at memory location is sent into MDR by data bus

4. program counter increments

5. contents of MDR copied into CIR

decode

- contents of CIR decoded by control unit

- decoded instruction split into opcode and operands

opcode

- specificies the operation

operand

- data for the operation

execute

instruction carried out

1. required data is fetched

2. instruction is carried out

3. results stored in general purpose registers or main memory

processor instruction set

specifc group of instructions carried out by the processor (stored in machine code, with operands and opcode

addressing modes

immediate addressing

direct addressing

immediate addressing

operand is datum

direct addressing

operand is address of datum

factors affecting processor performance

- number of cores

- cache memory

- clock speed

- word length

- address bus width

- data bus width