chapter 3: hardware

cpu

• performs fetch and execute

• directly accessed by main memory

3 components of cpu

• CU

• ALU

• registers and buses

CU

• performs decode stage

• sends control signals

• controls the flow of the cycle

ALU

• arithmetic logic unit

• performs logic and arithmetic calculations

• using ACC

what are the 5 special purpose registers

• pc

• acc

• cir

• mar

• mdr

PC

• program counter

• holds the address of the next instruction to be fetched from memory

MAR

holds instruction addres

MDR

holds instruction data

CIR

holds current instruction data at the CU to be decoded

ACC

temporarily holds values for the ALU

what are the 3 buses and what do they do

• adress bus: pc → MAR (unidirectional)

• data bus: MDR/CIR/IO devices (bidirectional)

• control bus : carry timing signals (bidirectional)

fetch stage

• pc holds next instruction address

• address copied to MAR using address bus

• data copied from MAR to MDR

• data copied through data bus

• to CIR

• pc value increments by one to point to next instruction

decode stage

• data held at CIR to be decoded by CU

• data passed on the CPU

• CU checks that IO devices are ready

• if they are, instruction data is passed onto alu for execute

execute stage

• ALU performs logic and arithmetic calculations required by the instruction

• ACC temporarily stores values for the ALU

CPU core

• one set of ALU, CU and register and buses

• can also be dual or quad core

clock speed

the number of electrical pulses produced by CPU each second

overclocking

• when the clock speed is too high for the computer

• can cause overheating

cache memory

holds regularly used data for quicker access in the cpu

word

a group of bits in a single unit

microprocessor

integrated circuit on a single chip

instruction set

the commands that can be processed by the cpu

opcode

the instruction / operation eg ADD

operand

the data being acted on

embedded systems

a combination of hardware and software designed to carry out a specific function

examples of embedded systems

• gps

• security systems

• lighting systems

• washing machines

• motor vehicles

benefits of embedded systems

• can be small and portable

• simple interface

• can be remotely controlled

• consume little power

• relatively cheap

drawbacks of embedded systems

• needs a specialist to troubleshoot issues

• difficult to upgrade

• can be hacked

• can be thrown away easily if out of date/ wasteful