Computers

A structure in which the hardware is connected and organised. It consists of Main Memory and a Central Processing Unit interconnected by buses. __________Main Memory ________ (Read)!_____¡(Write) Input –> Central Processing Unit –> Output The CPU reads and writes data & program instructions to and from main memory.

Known as Random Access Memory(RAM) It stores the data & programs the CPU can access. Volatile - Loses content when power is lost. Faster and more expensive than secondary storage

A computer that is multi-purpose, can be programmed to carry out different tasks. They are able to store program instructions and data in main memory.

Consists of: - Control Unit (CU) - Arithmetic Logic Unit (ALU) - Registers

• Decodes instructions received from main memory • Coordinates the actions of other components

Performs arithmetic and logic operations on data.

Provides fast, temporary storage for instructions.

Buses connect the components inside a computer. Types: - Address bus - Data bus - Control bus

Carries the address of the memory location. Unidirectional, only the CPU can put an address on this bus.

Holds the value being read from or written to memory. Bidirectional.

• Carries command signal from the control unit to other components. The status signal is sent back to the CPU. • Bidirectional.

A tiny quarts crystal that vibrates and sends out electronic signals to synchronise the actions of the hardware components. Measured in hertz, 1 hertz = 1 “tick” per second.

Program instructions and data are stored in main memory and transferred/fetched one data at a time to the CPU, where they are decoded and executed. Fetch: The control unit sends a read signal to main memory along the control bus. It also places the memroy address of the next instruction on the address bus. The RAM copies the content of the memory location indicated by the address bus on the the data bus. Decode: The control unit decodes the instructions. Execute: The control unit sends signal to the other components of the CPU instructing them what to do.

• Non-volatile • Allows the system to store data and programs permanently. • Cheaper and slower than main memory. Types: - SSD(Solid State Drives): USB drive - Magnetic storage: HDD(Hard Disc Drive) - Optical Storage: DVD/CD

• A head reads & writes to spinning discs. • An area that is magnetised represents a 1. • An area that is not magnetised represents a 0.

• Represents bits by little pools of trapped electrons on a microchip. • No flow(trapped) represents a 0. • Electron flow represents a 1.

• Laser beam reads and writes data(Pits and land) • Pit represents a 0 • Land represents a 1

A program that controls and manages the hardware and all other software on a computer and provides an interface for users

Programs or apps deigned for end users. Such as: - Web browser - Spreadsheet - Game

Programs that functionality to a computer system or improve its performance in some way. Such as: - Disk repair - Compression - Anti-malware

To produce software that is capable of handling the unexpected without crashing, not generating incorrect output, or not revealing sensitive data

• Not having a well-thought design • Not following coding standards • Using a temporary fix • Writing unstructured code • Not testing

• All processes are held in a queue • Some processes are prioritised • Processes are allocated time slides, length of time slices depends on priority. Processes are switched at the end of their time slice • Unfinished processes are put to the back of the queue • During the time slice, the process has exclusive use of the processor

• Relational • Arithmetic • Logical