4.1, 4.2, 4.3 Computer systems

CS GCSE AQA revision

Hardware

The physical components of a computer system which carries out the processes and displays the results

Software

The collection of programs and instructions that tell a computer how to perform specific tasks and operate hardware components.

Transistors

Electronic switches used be computers to store everything, with ON and OFF represented by binary symbols 1 and 0

Boolean Logic

True and false 1 and 0

Truth tables

Display all possible inputs and outputs for a logic system based on Boolean variables.

Not gate

An inverter, symbol is overbar

AND gate

Produces a 1 if both inputs are 1. Symbol is .

OR gate

Produces a 1 if either or both inputs are 1s. Symbol is +

XOR gate

Produces a 1 if exactly one input is 1. Symbol is + with a circle.

How many permutations/rows for a truth table

2 to the power of the number of inputs

Systems software

Controls the hardware inside the computer, provides an interface for users. It is comprised of the operating system and utility software

utility software

A collection of programs, help maintain computer system. It is not essential but helps it to run efficiently

4 types of utility software

Encryption, defragmentation, data compression, backup

Encryption software

Scrambling data so its not understood if read by unauthorised users. Uses an algorithm and key to change data into ciphertext, which need to be reused to decode the data. Some operating systems enable an authorised user to encrypt files which are automatically decrypted when re-accessed

Defragmentation software

data stored on a magnetic disk drive can be split into seperate blocks of data (if too big for one place) and saved to different areas where there is space. Defragmentation is reorganizing scattered data on a disk drive into contiguous sections- improves efficiency and speed by reducing the time it takes to read or write data.

Data compression

Algorithms that reduce the size of files so they take up less storage space, makes files more acceptable sizes to share

Lossy compression

Reduces file size by deleting some data

Lossless compression

Reduces the file size but does not delete any data

Compressed files

Can be transmitted quicker over the internet and require less bandwith

Backup software

Important data in secondary storage is at risk of being lost or damaged and so should be backed up

Application software

End-user programs that perform specific tasks, or used for entertainment (word processing, spreadsheets, playing games)

Operating system

controls the general operation of the system/device and provides a way for users to interact and run programs. controls hardware and is where apps run. example = windows

What does the OS manage

Processor, memory, input and output device, applications, security (management)

Processor Management

Processor management is the allocation of processor time to each task that needs to be carried out by the different progrms and processes running on a computer at any one time. Processor time is shared betweeen applications so that they appear to be running simultaneously.

What is memory management?

The memory management system keeps a record of where the data for eac program is being held so it can be fetched when needed. It controls the use of RAM by allocating blocks of free space in the main memory to each program that is being used. Memory is broken into blocks called ‘pages‘. The OS works out how much memory a program needs and allocates enough pages to hold the program and its files. When the progam is closed, its pages are freed up and able to be used again.

What are peripherals

Input or output devices connected to a computer

What is input/output device management

Peripherals are controlled by their own device driver (small program allowing the peripheral device to communicate with the computer), The device manager controls the data being sent between the computer and the devices.

Application management

Apps can’t functions without an OS, which runs a program in order to install new apps and then interacts with them through the applications program interface (API)

What is the API

It allows the application to communicate with the operating system, allocating memory space for it to be loaded and queueing jobs that need to be allocated processor time. It is a set of rules that allow communication

How does the OS help keep the system secure from threats (Security management)?

1. Access to the computer is controlled through user accounts

2. Users need to enter passwords to access the software/files on a computer

3. Different access rights set for each user, controlling what they can do

4. Updates to the OS can be downloaded automatically to keep security effecient and up-to-date

5. Data stored in secondary storage can be encrypted to ensure it stays secure

types of OS

windows and android