OCR: GCSE Computing A451 Flashcards
Computer System
A combination of hardware and software components that allow input, processing
and output of data.
Hardware
The physical components that make up a computer system.
Software
The programs that run on a computer system.
Input Device
Hardware that accepts data into the computer. They take real world analogue data and convert it into a digital form that can be stored on a computer. For example: keyboard, mouse, microphone, webcam, scanner, sensors.
Output Device
Hardware that presents the results of processing to the user or actuators that perform a task automatically. They use digital data from a computer and produce it in a form that is understandable or usable. For example: monitors, printers,
speakers, projectors, actuators (motors).
Storage Device
Hardware that is used to store files long term and is non-volatile, such as hard
disks, memory sticks, magnetic tapes and CDs.
System Reliability
How far you can depend on the computer system being available when you need
it. Usually measured in terms of availability.
System Availability
The proportion of time that a system is operational, usually expressed as a percentage over a period of time. E.g. 95% measured over one year.
Mean Time Before Failure (MTBF)
Mean Time Between Failure: a measure of availability often quoted by hardware
manufacturers. For example 2.56 years between failures means that, on average, the hardware can be expected to last 2.56 years before it goes wrong.
System Redundancy
Spare hardware components are built into a system so that, in the event of a component failing, the system can swap over to the spare one.
System Disaster Recovery
Where a company has plans to replace a system quickly if there is a catastrophe (fire, flood, bomb etc). Designed to minimise the time the system is down.
CPU
The central processing unit that contains the processor, main memory and cache.
(sometimes people say CPU when they mean processor so look for the context).
Main Menory /RAM
Also known as Immediate Access Store and Primary Memory The memory in the CPU that is used to temporarily store programs while they are running and the data used by these programs. The processor fetches instructions from main memory. Memory is made up of many addressable locations.
Processor
The component in the computer that fetches, decodes and executes instructions.
Cache
High speed memory in the CPU that is used to store a copy of frequently used
instructions and data. Faster access speed than main memory. Used to improve
CPU performance.
Clock Speed
Measured in hertz or cycles per second, the clock speed represents how many
instructions per second the processor can execute. The higher the clock speed the
faster the CPU can operate.
System Busses
The circuits/internal wiring that connect the processor and main memory.
Fetch-Execute Cycle
The process by which a program is run: instructions are stored in main memory,
fetched by the processor one at a time, decoded and executed.
Dual-Core/Quad Core
A CPU that contains multiple processor components (cores) that can operate independently to process more than one task at a time.
RAM
Random Access Memory: a type of memory that is read-write and volatile.
Used for Main Memory.
ROM
Read Only Memory: memory that is hard-coded at the time of manufacture. Stores the startup program, called the bootstrap loader.
Bootstrap Loader
The first program that is loaded into main memory from ROM when a computer is
switched on. This will load the operating system from secondary storage.
Volatile
Describes memory that loses its contents when the power is turned off, e.g. main memory
Non-Volatile
Describes memory that does not lose its contents when the power is turned off, e.g. hard disk.
Secondary Memory
Long term, non-volatile storage media such as hard disks, memory sticks, magnetic tapes, DVDs and CDs.
Virtual Memory
Part of the hard disk that is configured to behave as an extension to main memory.
Magnetic Media
Secondary storage such as hard disks, tape and floppy disks.
Optical Media
Secondary storage that is read using lasers such as CDs and DVDs.
Solid State / Flash Memory
Secondary storage that has no moving parts. Used in memory sticks, cameras and phones.
Pen Drive
Another term for a USB memory stick
Boolean Expression
An expression that is either true or false, e.g. X=10
Truth Table
A table that shows all the possible combinations of inputs and their logical
output value.
Logical Operators
AND, OR, NOT
Logic Diagram
A diagram of a circuit showing logic gates with inputs and the output these generate.
Software
Programs that run on the computer.
System Software
Programs that are used to run the computer, including the operating system, utilities, library routines and programming language translators.
Application Software
Programs that perform a task for a user, such as word processing, timetabling, accounts or payroll.
Operating Software
System software that is necessary for the computer to function.
Utility Software
System software that provides other useful functions for operating the computer or performing computer-related tasks such as anti-virus
programs.
Library Software
System software modules that perform frequently required tasks. They can be built into or called from other programs.
Translators
System software that translates high-level programming languages into
machine code. Includes compilers and interpreters. (An assembler translates low-level assembly code into machine code.)
Memory Management
One of the main functions of the operating system – allocating space in main memory to all currently running programs and their associated data, and recycling the space when they have finished.
Peripheral
A device (hardware) that is connected to the CPU to provide input, output or storage
Peripheral Management
One of the main functions of the operating system – managing the input to and the output from the CPU.
Multi-tasking
One of the main functions of the operating system – managing how several tasks or programs, which are all running at the same time, share the processor.
Security
One of the main functions of the operating system – protecting the computer system from various hazards such as unauthorised users, viruses, hackers and accidental damage.
User Interface
The method of communication between the computer and its user. Sometimes called HCI (Human-Computer Interface) or MMI (Man-Machine Interface).
HCI
Human-Computer Interface: another term for user interface.
MMI
Man-Machine Interface: another term for user interface.
GUI
Graphical User Interface. A style of user interface, which is based on icons rather than text.
WIMP Interface
Stands for: Windows, Icons, Menus and Pointers. It describes a type of user interface where the user selects icons and menu items with a pointer of some kind (with a mouse, stylus or finger).
Command-Line Interface
A style of user interface that is only text-based. Commands are typed in at a text prompt.
Address
A numerical reference to a location in memory.
Process
A program that is running in main memory.
Virus
A program that is installed on a computer without your knowledge or permission with the purpose of doing harm. It includes instructions to replicate automatically on a computer and between computers.
Antivirus Software
A utility program that prevents harmful programs being installed and important files being changed. The antivirus software scans all the files
on the computer periodically and if a virus does install itself, it detects and removes it.
Firewall
A utility program that prevents unauthorised access to computers or a LAN from the Internet and controls what sites computers on the LAN can access.
Spyware
A program that secretly records the user’s actions on the computer including passwords and personal details they type when accessing a secure site.
Disk Defragmenter
A utility program that optimises the use of the hard disk space by collecting together the separate segments of each file into contiguous blocks (i.e. blocks next to each other) on the disk as well as grouping together the blocks of free space so newly saved files do not have to be fragmented (split up).
System Cleanup
A utility program that deletes unnecessary files and settings to optimise the computer’s performance.
Automatic Update
A utility program that, for any software already installed on the computer, will regularly check on the Internet for newer versions and updates, then download and install them.
System Information and Diagnosis
A utility program that presents information about the computer hardware and usage as well as information to help diagnose problems.
Formatting
A utility program that formats secondary storage devices such as hard disks, preparing them for use.
File Transfer and File Management
A utility program that allows the user to create a logical view of how their files are organised using folders. Allows the user to move files
and folders, copy, paste, name and delete files and folders.
Open Source
Software that is supplied with its source code. The source code can be modified and the software redistributed (as long as this too is open source).
Licence
An agreement that defines the conditions for using the software.
Freeware
Software that is provided free of charge under licence but without the source code. It is copyrighted and cannot be modified.
Proprietary Software
Software that is copyrighted and the licence sold under a patented or trademarked name.
Off-the-Shelf Software
Software that can be purchased from a High Street or online store. Not custom-written.
Custom-Written Software
Software that is written for one customer’s specific requirements.
What is a bit?
A single binary digit: 1 or 0
How many bits in a byte?
8 bits
How many bits in a nibble?
4 bits
How many bytes in a kilobyte?
1024 bytes
How many kilobytes in a megabyte?
1024 kilobytes
How many megabytes in a gigabyte?
1024 megabytes
How many gigabytes in a Terabyte?
1024 gigabytes
Binary
Base 2 number system, used by computers, uses the digits 0 and 1 only.
Denary/Decimal
Base 10 number system, how we normally count, uses digits 0 to 9.
Hexadecimal
Base 16 number system used by humans to represent groups of four bits at a time. Uses digits 0 to F.
Overflow
When the result of a numeric calculation is too large to be stored in the space reserved for that type of data.
Character set
The set of symbols that can be represented by a computer. The symbols are called characters and can be letters, digits, space, punctuation marks and some control characters such as “Escape”. Each character is represented by a numerical code that is stored as a binary integer.
ASCII
American Standard Code for Information Interchange: a 7-bit character set used by PCs. (There is also an extended ASCII character set that uses 8 bits.)
EBCDIC
Extended Binary Coded Decimal Interchange Code: an 8-bit character set used by older mainframes.