Unit 5 - Computer Architecture

Dedicated registers

Memory locations used to assist in operation of the CPU

(PC) Program Counter

Holds the memory address of the next instruction to be read from memory

(CIR) Current Instruction Register

Holds the current instruction

(MAR) Memory Address Register

holds the address in memory where the processor is required to fetch/store data from

(MBR) Memory Buffer Register

Temporarily holds the data moving between the CPU and Main Memory

(SR) Status Register

Holds information about the current state of operations. It detects errors

Cache

Small amount of high speed memory that stores frequently used data from the user

Number of cores

More cores means more instructions can be processed simultaneously.

Interrupts

It is a signal by a software program or a hardware device sent to the CPU.

Word length

amount of data the CPU can process simultaneously

Registers

are temporary

Control Unit

Controls the flow of data

Arithmetic Logic Unit

Performs arithmetic

CPU

the brain of the computer. It processes all instructions in the computer.

Device drivers

Software that interacts directly with I/0 controllers

RAM

Temporary, volatile storage. It stores the files and programs being used currently by the user.

ROM

Permanent, non-volatile storage. Contains BIOS for the computer to start up.

Data bus

sends data between CPU components

Address bus

sends memory addresses from the CPU to CPU components

Control bus

sends control signals between I/O Controllers and the CPU

John Von Neuman

Instructions and data are stored in a common main memory and transferred using a single shared bus.

Harvard Architecture

Separates data and instructions into separate memories using different buses.

Computer system

Any device that can take a set of inputs and process them into useful outputs

I/O controllers

Hardware that interacts between the computer CPU and external peripheral devices

Device drivers

Software that interacts directly with I/0 controllers 

Tasks of the I/O Controller

I/O controllers convert signals sent from peripheral devices into a format for the computer to process

What is the purpose of control lines?

Prevent conflict between the data and address bus when different components access them

Buses

A series of wires that transfer data signals between internal components

What affects the data buses performance?

Width of the data bus

What way does the Address Bus carry data?

One direction

What way does the Data Bus carry data?

Both directions

What way does the Control Bus carry data?

Both directions

What does the width of the Address Bus do?

Determines the maximum possible memory capacity of the system

What operations can the ALU carry out?

Arithmetic:+ * / -

Logical: NOT AND OR 

Shift: Shifts bits

System clock

Synchronises the operations of the processor components

Accumulator

Stores the immediate results of the ALU

Factors that affect CPU performance?

Word length

Data bus width

Determines how many bits can be transferred simultaneously

Interrupts

It is a signal by a software program or a hardware device sent to the CPU

2 types of interrupts

• Software interrupt - Application program terminates

• Hardware interrupt - When I/O has an error like a printer displaying “out of paper”.

Memory Write: Control Signal

Memory write: causes data on the data bus to be written into the addressed location

Memory Read: Control Signal

Causes data from the addressed location to be placed on the data bus 

Bus Request: Control Signals

Bus request: indicates that a device is requesting use of the data bus

Bus Grant: Control Signal

indicates that the CPU has granted access to the data bus

Clock: Control SIgnal

Used to synchronise operations

Instruction Set

Describes the commands a processor can perform

Immediate Addressing

(00) - immediate addressing - Holds actual data

Direct Addressing

(01) - Holds an address, not a piece of information

Address Mode

It tells the processor what type of data is in the operand. Is it actual data, memory address or register.

Operation code (Opcode)

Includes command of the instruction and the addressing mode.

Operands

One or more items of data that are used in the instruction.

How does a barcode work?

Light from a laser is directed at the pattern and a sensor detects the intensity of the light that bounces back.

A black bar absorbs more light - less reflective, giving a binary of 1

A white bar is morereflective, giving a binary of 0

QR Codes

They are 2D barcodes that can be read by phones

Uses: Restaurant coupons, tourist information, mobile concert tickets