Computer Systems

specification

configuration of a computing system, such as:

• hardware components

• technical characteristics

secondary storage

a set of components that store programs and data

• it still retains content when the power is off. e.g. hard disks or USB drives

• all types except RAM and ROM

main memory

the component that stores programs/data currently in use.

• these are volatile, meaning they are lost when the computer is off

• this is known as RAM(random access memory)

RAM

random access memory—- accessed from any location in memory

ROM

read-only memory, non-volatile.

• ideal for storing instructions and data that are needed for the computer to run.

processor

the component that executes program instructions

e.g. arithmetic operations, input/output of data, control program flow

CPU

central processing unit

how processors work

instructions are fetched one by one from memory, the processor executes each instruction, data is moved to memory/

a program’s execution

storage » memory » processor

• yarns and needles on a shelf

• resources temporarily moved to a coffee table

• knitter looks at knitting pattern and does the knitting

communication components

how computer systems exchange and share information

input/output

how computing systems interact with the user and their surroundings.

input

data received, e.g. keyboard and mouse

output

data transmitted, e.g. printer, headphones

transistors

located inside processors, storing zeroes and ones.

early computers

• no single memory for everything

• no general purposes

• programs weren’t stored in memory

• slow and inflexible

Von Neumann architecture

a computer architecture where both instructions and data are stored in a single, shared memory space.

Von Neumann architecture characteristics

• single processor

• one memory for instructions & data

• programs & data implemented one at a time

structure diagram

CPU circuit

integrated circuit that performs calculations

1= current passes through

0= current doesn’t pass

controller/ control unit

sends and receives signals from all parts of the computer, ensuring that all processes take place at the right time & in the correct order.

Bus

used to send control signals and data between processor and components

Control bus

manages communication between memory, input and output

data bus

exchange between all components

address bus

gets memory to ALU

ALU

Arithmetic and Logic Unit, processes and manipulates data.

• performs simple calculations on data that’s temporarily stored in registers

Register

storage location found in CPU where data or control information is temporarily stored.

• faster than internal memory since they are often accessed

internal memory

data is moved from registers to internal memory when not actively used.

• (cache memory)

• fast access, temporary storage on CPU.

main memory(in circuit)

describes computer memory used to store programs & data while being used by the CPU

• only directly access data & programs if they’re in main memory

• mainly RAM, ROM when computer is first turned on

cache memory

used between main RAM & CPU

• improves performance by holding data that will be/has been processed

factors affecting CPU

processor speed = clock speed, measured in Hz

• the faster that is, the faster a processor can run the fetch-decode-execute cycle.

1 tick per second = 1 Hz

c

core

used to describe the processing components within the CPU