Vocabulary Flashcards
ASCII -
a character set. Each letter on the keyboard has a unique ASCII value that can be represented in hexadecimal or decimal.
Bit -
Binary Digit. Either 1 or 0, On or Off.
Byte -
Smallest unit or memory. A collection of 8 bits.
Gigabyte (GB) -
1024 megabytes. 2 to the power of 30 bytes.
Kilobyte (KB) -
1024 bytes. 2 to the power of 10 bytes.
Megabyte (MB) -
1024 kilobytes. 2 to the power of 20 bytes.
Memory dump -
output of memory contents onto the printer or screen. Usually represented in hexadecimal.
Petabyte (PB) -
1024 terabytes. 2 to the power of 50 bytes.
Spooling -
Data are temporarily held in a buffer waiting for an output device to access it.
Terabyte (TB) -
1024 gigabytes. 2 to the power of 40 bytes.
Asynchronous data transmission -
Data sent in an agreed bit pattern with control bits. The received knows when the transmission starts and ends.
Checksum -
The sum of all the bytes in a transmission is sent with the data. Used with credit card numbers. Checks whether data has been changed or corrupted following transmission.
CSS –
Cascading Style Sheet. Controls presentation of page. Enable multiple pages or elements on a page to be changed in one go.
Echo Check -
Data is sent to another device and is sent back again to the sender. The two sets of data are compared to spot any errors.
Even Parity -
Used with parity checking and parity bits where each byte of data has an even number of 1 bits in it.
Full duplex data transmission -
data can be sent in both directions at the same time.
Half-duplex data transmission -
data can be sent in both directions but only one at a time. e.g. walkie talkies
HTML –
HyperText Mark-up Language. Used to write and develop webpages to present text. Uses tags.
HTTP -
Hypertext Transfer Protocol. Protocol used by web browsers
HTTPS –
Hypertext Transfer Protocol Secure. A set of rules to be followed when transferring files across the Internet. The S is for secure with private data.
IP address –
a number assigned to each device on the Internet. Assigned by ISP. Gives you the location. MAC address gives you each person in the location.
ISP –
Internet Service Provider. A company you pay to give access to the Internet.
MAC address –
Media Access Control. A number that uniquely identifies a device on the Internet. Often refers to network card. Rarely changed. Usually 12 or 16 hex digits. First 6 or 8 refer to manufacturer code. Last 6 or 8 is the serial number of the device.
Odd parity -
used with parity checking where each byte has a parity bit. Each byte would have an odd number of 1s in it.
Parallel data transmission -
several bits (usually one byte) are sent down several wires at the same time. Risk of skew when bits arrive out of sync.
Parity Check -
A method to check whether data has been changed or corrupted following data transmission. Uses odd or even parity
Serial data transmission -
data is sent one bit at a time over a single wire. Goo d over longer distances.
Simplex data transmission -
data sent in one direction only. e.g. computer to printer.
URL –
web address. Consists of protocol, web server name and file name.
USB -
Universal Serial Bus. An asynchronous serial data transmission method. (Never use USB as a replacement term for memory stick).
Web browser –
software which allows a user to display a web page on their computer screen
Address Bus -
Carries address of the next item to be fetched. Unidirectional.
Architecture -
How a computer system is designed.
ARQ -
Automatic Repeat Request. Checks whether data has been correctly transmitted by sending an acknowledgement that data has been sent correctly. A timeout is the time allowed to pass before an acknowledgement is received. If no acknowledgement is received before the timeout elapses, the message is automatically resent.
Buffer -
A temporary memory area in a device.
Control Bus -
Carries signals relating to the control and co-ordination of all activities within the computer (e.g. read/write functions). Unidirectional or Bidirectional.
Control Unit -
Controls the operation of the memory, processor and input/output devices
CIR (Current Instruction Register) -
Stores the instructions that is currently being executed.
Data Bus -
Carries data that is currently being processed / that will be / that has been processed between the processor, the memory unit and the input/output devices. Bi-directional.
Fetch-Execute Cycle -
A feature of Von Neumann architecture. Data is fetched from the memory address in the PC, stored in CIR, then the PC is incremented. Instruction is then decoded and executed.
Interrupt -
a signal that causes the operating system to take a specified action
MAR (Memory Address Register) -
Contents of the PC are copied to the MAR via the address bus.
MDR (Memory Data Register)
- Contains the contents of the memory location specified in the MAR.
Memory Management -
A process of assigning blocks of memory to programs running in a computer
Memory Unit -
Made up of addresses and contents. Identifies every location in memory and the contents of each location.
Multi-tasking -
Many processes appearing to the user to run simultaneously.
Operating System -
The software running in the background of a computer system. It manages many of the basic functions such as multi-tasking, error handling, memory management, input and output control and human computer interface.
Parity bit -
Set to 1 or 0. Sent with a byte of data to make the total number of 1s odd or even for each byte.
PC (Program Counter) -
Contains the address of the memory location of the next instruction to be fetched.
Register -
High speed storage area within the computer.
Utility -
A program that performs a specific task required for the operation of a computer system.
Von Neumann Architecture -
computer architecture that holds programs and data in memory. Data moves between the memory unit and the processor.
Actuator -
An electro-mechanical device used in control applications with sensors. Examples would be relay, solenoid or a motor.
ADC -
Converts physical values into discrete digital values. Could be used in speech recognition. Analogue Digital Converter.
Additive Manufacturing -
Used by 3D printers to build up an object layer by layer.
Barcode -
Series of dark and light lines of varying thickness representing binary values. No need to price each item and allows automatic stock control. Guard bars separate the left and right hand side of the barcode.
Binder 3D printing -
Two passes for each layer. First sprays dry powder, the second a binder (type of glue) is added to make a solid layer.
Capacitive Screen -
made up of layers of glass that act like a capacitor. Electric fields are created between the layers which changes when touched. Allows multi-touch.
CCFL -
Cold Cathode Fluorescent Lamp. Before LEDs, this method was used for backlighting.
Concept Keyboard -
a flat board with buttons. Each button can be programmed to do whatever you want. Ideal at a fast-food checkout for example.
CT Scanner -
Computed Tomographic Scanner creates a 3D image of a solid object by taking very thin “slices” with X-rays or radio frequencies.
Control System -
a computer system that uses sensors to alter devices according to criteria. E.g. street lighting, traffic control, burglar alarm.
DAC -
Digital to Analogue Converter. Sound can be produced by passing digital through a DAC to an amplifier and then to a speaker.
Direct 3D printing -
works like an inkjet printer. The print head moves left and right and also up and down to build up the layers of an object.
DLP -
Digital Light Projector. Contains millions of micro-mirrors on the DLP chip. When tilted towards the light source they are on. When tilted away, they are off.
Infra-Red Screen -
Uses glass as the screen material. A grid of sensors work out the co-ordinates being touched from the change in temperature. Allows multi-touch.
Inkjet printer -
best for one-off photos or a few pages of high quality colour printing
Input Device -
a device that allows the computer to receive data from the outside world.
Keyboard -
each character on a keyboard has an ASCII value. Each character pressed is converted into a digital signal interpreted by the computer. RSI can result from too much use.
Laser printer -
used for high quality multiple printouts e.g. an advertising poster. Uses dry, powdered ink.
LCD -
Liquid Crystal Display. A screen with the front layer made up of liquid crystal diodes. 3 or 4 of these diodes together make up pixels.
LED -
Light Emitting Diode - a screen that provides better contrast and brightness than CCFL.
MIDI -
A set of instructions for digital instruments to play synthesised sounds. Musical Instrument Digital Interface. Does NOT contain any music itself.
Monitoring system -
a computer system that uses sensors to report the status of a system. E.g. patient’s vital signs.
OCR -
used with scanners to convert scanned text into a text file format. Optical Character Recognition.
OLED -
Organic Light Emitting Diodes. Organic film is sandwiched between two charged electrodes (one is a metallic Cathode and the other a glass Anode). When an electric field is applied, the electrodes give off light. There is no need for backlighting.
Output Device -
a piece of hardware used to communicate the results of data processing carried out by the computer.
QR Code -
A 2D matrix of filled in dark squares on a light background that is scanned with a mobile phone and holds more information than a normal barcode. Used for advertising.
Range Check -
Checks that only numbers within a specified range are accepted. E.g. 0 to 100.
Removable hard disk drive -
a hard disk drive that is connected via a USB port. Used as a backup device or to transfer data between machines.
Resistive Screen -
One upper layer of polyester and a bottom layer of glass. When top layer is touched it completes a circuit which is interpreted by a microprocessor to determine the co-ordinates. Allows multi-touch.
RSI -
Repetitive Strain Injury from frequent use of devices such as a keyboard.
Sampling Rate -
the rate at which the DAC can convert the digital output into analogue voltages. The standard rate is 41,100 samples per second
Sensor -
sensors send data from the real world to a computer. They form part of a monitoring or control system. They use an ADC so the computer can understand the data.
Subtractive Manufacturing -
Used by 3D printers to remove material to create the object (e.g. making a statue out of a block of stone).
Synchronous data transmission -
A continuous stream of data accompanied by timing signals from the internal clock. Faster than asynchronous and no timing bits used.
Tracker ball -
A pointing device where a ball on top of the tracker ball moves the cursor. Ideal for environments with little space. Users are less likely to suffer injuries such as RSI.
USB Flash Memory -
Solid state storage device. Small and lightweight.
Birefringence -
Reading errors of optical media such as DVD due to the two sandwiched layers. Blu-Ray has only one layer so avoids this problem.
Blu-Ray -
Optical storage that uses a blue laser rather than a red laser for CD or DVDs meaning the pits and bumps can be smaller and therefore store more.
DRAM -
Dynamic RAM has a number of transistors (like a switch) and capacitors (that hold 0s and 1s). DRAM needs to be refreshed (recharged) all the time, but are cheaper to make than SRAM, consume less power and hold more data.
DVD -
Optical Media. Can be -R or -RW. Holds more data than a CD
DVD-RAM -
Contains concentric tracks to allow simultaneous read and write operations.
SRAM -
Static RAM that uses flip-flops to hold each bit and does not need to be refreshed. It is faster than DRAM.
Solid State Drives -
A storage drive that has no moving parts.
CD -
Optical Media. Uses a red laser to write and read data. Can be -R (write once, read many) or -RW (rewriteable).
.FLAC -
lossless compressed music files.
JPG (or JPEG) -
lossy image file. Common for website images.
Lossless image compression -
finds groups of repeating data. Records the data once and the number of times it was repeated. e,g. PNG
Lossless text compression -
finds the patterns in the original text. Encodes each of the patterns into a dictionary.
Lossy Compression -
Permanently removing data when compressing file e.g. MP3, JPEG
MP3 -
lossy music format.
MP4 -
multimedia file format (video and audio)
Off Line Storage -
Non-volatile memory that can be removed from a computer system. CDs, DVDs, DVD-RAM and Blu-Ray Disks
Optical Storage Devices -
CDs and DVDs that are written to with a laser light and the data stored in “pits” and “bumps” on the spiral track.
PNG -
Lossless picture file format that uses alpha channel to keep transparent backgrounds.
Primary Memory -
memory directly accessed by the CPU (ROM/RAM/DRAM/SRAM are examples)
ROM - Read Only Memory -
Primary memory that is permanent, cannot be changed and stores the start-up instructions when the computer is first turned on.
Secondary Storage -
Memory not directly accessed by the CPU, but allows a user to store data that can easily be accessed by applications. Hard disk drives, solid state drives are examples.
.WAV -
uncompressed music files
Assembler -
Translates a low level programming language into machine code. An executable file of machine code is produced.
Assembly -
A low level programming language that needs to be translated into machine code by an assembler.
Integrated / Interactive Development Environment (IDE) -
Used for program development. Contains an editor, an interpreter or complier and debugging tools.
Logic Error -
where a program does not do what the programmer wanted it to do.
Machine Code -
the binary instructions that a computer understands. No translation is necessary.
Program -
A list of instructions that enable a computer to perform a specific task.
Syntax Error -
Where a program does not obey the rules of the programming language.
Translator -
Translators convert a program into binary instructions that computers can understand.
Authentication -
Used to verify that data comes from a trusted source. E.g. passwords or biometrics.
Cookie –
a file sent by a web server to a web browser. Not a program. Store user preferences. Resides on client machine, not server. No personal data held.
Cracking -
the editing of a program’s source code so it can be exploited or changed for a specific purpose.
Cypher Text -
The output from an encryption algorithm
Denial of Service (DoS Attack) -
An attempt at preventing users from accessing part of a network.
Encryption -
Scrambles data for secure transmission.
Ethics -
a set of principles set out to regulate the use of computers.
Erroneous data -
test data that should be rejected by the system as not being suitable.
Firewall -
Uses rules and criteria, set by the user, to help protect a network or systems from unauthorised access.
Free software -
Users have the freedom to run, copy, change or adopt free software.
Freeware -
software that can be downloaded free of charge. Still subject to copyright laws.
Hacking -
the act of gaining illegal access to a computer system without the owner’s consent or knowledge.
Pharming -
Malicious code installed on a user’s hard drive or on the web server; the code will send the user to a fake/bogus website without their knowledge. User needs to click on link.
Phishing -
sending out a legitimate-looking email. When the recipient clicks on a link in the email, they are sent to a bogus/fake website. Requires the user to click on a link.
Plain Text -
text before it goes through encryption program
Private Key -
a key used in asymmetric encryption. Known only by the computer user.
Proxy Server -
Computer that acts as intermediary between a web browser and the Internet.
Public Key -
a key used in asymmetric encryption. Available to everybody.
Secure Socket Layer (SSL) -
Provides a secure connection between web browsers and websites allowing secure transmission of private data.
Shareware -
Users can try a version for a limited time before needing to pay for it to carry on using it. Features are often limited in shareware.
Spyware -
software that gathers information by monitoring keyboard presses and sends it back to the person who made the software.
Symmetric Encryption -
A secret key (combination of characters) which when applied to a message, makes the message contents unreadable unless the recipient has the decryption key.
Transport Layer Security (TLS) -
A protocol designed to ensure that no third party may eavesdrop or tamper with any message.
Viruses -
program or program code that can replicate/copy itself with the intention of deleting or corrupting files or cause the computer to malfunction.
Wardriving -
to locate and use wireless internet connections illegally. Needs a laptop, wireless network card and an antenna to pick up the signals.
Presence Check -
Ensures that some data has been entered and the value is not blank. E.g. email address must be provided on an online transaction.
Character Check -
Checks that when a string of characters is entered, it contains no invalid characters (e.g. %).
Check digit –
a final digit calculated from all the other digits. Used to identify errors in mis-typing or mis-scanning a bar code. E.g. ISBN.
Computer System -
made up of software, data, hardware communications and people.
Extreme data -
data used for testing algorithms where a given range of data is allowed. Extreme data are the largest and smallest values the normal data can take.
Format Check -
Checks that the characters entered into a system conform to a pre-defined pattern. E.g. XXX-9999.
Length Check -
Checks that data contains either an exact number of characters or conforms to a range e.g. surname would have to be at least 2 and at most 30 characters long.
Library Routine -
a set of a programming instructions for a given task that is already available for use.
Normal data -
A set of test data for a system. Used with a set of results to check all results are as expected.
Top-down design -
the breaking down of a computer system into a set of sub-systems, then breaking each sub-system down until each sub-systems performs one function.
Type Check -
Check that the data entered into a system is of a given data type (e.g. integer)
Validation -
The automated checking by a program that data is reasonable before it is accepted onto a computer system. Examples include: range check, length check, type check, character check, format check, presence check and check digit.
Verification -
Checking that data has been accurately copied onto the computer or transferred from one part of a computer system to the other. Methods include: double entry, visual check, parity check, checksum.
Compiler -
A computer program that translates a program written in a high level language into machine code so it can be used by a computer to perform a required task. An executable file or object code is produced. A report of errors is generated. Optimises the source code.
High level language -
Closer to English. Require no knowledge of the hardware of the computer. High level languages are portable and can be used on different types of computer. Python or Java are examples.
Interpreter -
Translates a program one line of code at a time. Machine code is directly executed. The interpreter is used each time the code is executed. No file is produced. Will identify an error as soon as it finds one in a line of code. Stops on errors.
Low Level Languages -
relate to the specific architecture and hardware of a particular machine.
Boolean data type -
Has two values only - True or False
Char -
a variable consisting of a single character.
Constant -
A named data source that contains a value that does not change during execution of a program.
Integer data type -
A positive or negative whole number.
Real data type -
a positive or negative number with a fractional part.
Sequence -
Programming statements are followed in sequence.
String data type -
A variable of several characters (letters or digits or any other printable symbol)
Variable -
A named data source that contains a value that may change during execution of a program.
