Cambridge IGCSE Computer Science
HTTP - hypertext transfer protocol *** a set of rules which must be followed when transferring files
across the internet
URL - uniform resource locator *** used to find/identify a webpage on the internet 1. webserver name
2. file name 3. protocol
web browser *** software that allows a user to display a webpage on their screen - they interpret html
code and show the result
actuator *** used in many control operations involving sensors and ADC/DACs. Electromagnetic device
eg. motor that outputs result of sensor operation
loudspeaker *** output device that produces sound using voltages at different levels which vibrate a
cone in speaker housing
LED *** Used for backlighting a monitor/tv - they are thin, produce a white light, and do not require
much power
CCFL *** Old technology used for backlighting - took time to warm up, and produced yellow-ish lighting
+ required a lot of power
volatile *** memory that loses its contents when the power is off eg. main memory
non-volatile *** memory that doesn't lose its contents when the power is off e.g. hard disk
off-line storage *** storage that can be physically moved away from a device and stored somewhere
else e.g. CD, USB stick, DVD
,SRAM *** type of RAM that has 'flip flops' to hold each bit of memory. Does not need constant
refreshing.
magnetic media *** secondary storage with mechanical parts which move over the surface to read and
write data magnetically e.g. a hard disk, tape or floppy disk
program *** our way of telling a computer what to do, how to do it, and when to do it
assembly language *** code that is specific to a particular hardware, but needs to be translated into
machine code before it can run
machine code *** the binary code that is specific to a machine and does not need translating in order to
run
translator *** program that changes higher level language into machine code
compiler *** this translates HLL into machine code. Once it has done this, the program can be used
multiple times without translating it again
UPS *** uninterruptable power supply
cracking *** editing source code with malicious intent
firewall *** this examines traffic between a user's computer and the internet by checking what is/isn't
allowed and blocking traffic that does not meet certain criteria
,proxy server *** this filters web traffic, keeps the IP address secret, and, using a cache, speeds up access
to websites that have been visited before
TLS - Transport Layer Security *** this is a form of secure data transmission made up of 2 layers: the
record protocol, and the handshaking protocol. It is very secure and fairly new, and can make use of
session caching, which improves performance. It involves many complicated encryption algorithms.
prevents third party hacking into communication between web server and the user's computer.
session caching *** this is used in TLS to avoid using too much computer time; TLS is able to attempt to
resume an existing session, which increases speed.
Denial of Service (DoS) attack *** attempting to prevent a user from accessing part of a network (usually
the server); this is usually temporary, but may be very damaging, or a big security breach. overloads web
traffic by sending thousands of requests.
free software *** software that is free to run, copy, change or adapt, and share with friends, family or
colleagues.
CSS *** Cascading Style Sheet. Controls presentation of page. Enable multiple pages or elements on a
page to be changed in one go.
Gigabyte (GB) *** 1024 megabytes. 2 to the power of 30 bytes.
HTML *** HyperText Mark-up Language. Used to write and develop webpages to present text. Uses
tags.
Terabyte (TB) *** 1024 gigabytes. 2 to the power of 40 bytes.
Lossless image compression *** Find groups of repeating data. Records the data once and the number
of times it was repeated.
, Lossless text compression *** Finds patterns in original text. Encodes each pattern in a dictionary
PNG *** Lossless picture file format that uses alpha channel to keep transparent backgrounds.
MIDI *** A set of instructions for digital instruments to play synthesised sounds. Musical Instrument
Digital Interface.
.WAV *** uncompressed music files
.FLAC *** lossless compressed music files
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.
1KB (kilobyte) *** 1,024 bytes (2¹⁰ bits)
1MB (megabyte) *** (2²⁰ bits)
1GB (gigabyte) *** (2³⁰ bits)
1TB (terabyte) *** (2⁴⁰ bits)
1PB (petabyte) *** (2⁵⁰ bits)
A *** 10
HTTP - hypertext transfer protocol *** a set of rules which must be followed when transferring files
across the internet
URL - uniform resource locator *** used to find/identify a webpage on the internet 1. webserver name
2. file name 3. protocol
web browser *** software that allows a user to display a webpage on their screen - they interpret html
code and show the result
actuator *** used in many control operations involving sensors and ADC/DACs. Electromagnetic device
eg. motor that outputs result of sensor operation
loudspeaker *** output device that produces sound using voltages at different levels which vibrate a
cone in speaker housing
LED *** Used for backlighting a monitor/tv - they are thin, produce a white light, and do not require
much power
CCFL *** Old technology used for backlighting - took time to warm up, and produced yellow-ish lighting
+ required a lot of power
volatile *** memory that loses its contents when the power is off eg. main memory
non-volatile *** memory that doesn't lose its contents when the power is off e.g. hard disk
off-line storage *** storage that can be physically moved away from a device and stored somewhere
else e.g. CD, USB stick, DVD
,SRAM *** type of RAM that has 'flip flops' to hold each bit of memory. Does not need constant
refreshing.
magnetic media *** secondary storage with mechanical parts which move over the surface to read and
write data magnetically e.g. a hard disk, tape or floppy disk
program *** our way of telling a computer what to do, how to do it, and when to do it
assembly language *** code that is specific to a particular hardware, but needs to be translated into
machine code before it can run
machine code *** the binary code that is specific to a machine and does not need translating in order to
run
translator *** program that changes higher level language into machine code
compiler *** this translates HLL into machine code. Once it has done this, the program can be used
multiple times without translating it again
UPS *** uninterruptable power supply
cracking *** editing source code with malicious intent
firewall *** this examines traffic between a user's computer and the internet by checking what is/isn't
allowed and blocking traffic that does not meet certain criteria
,proxy server *** this filters web traffic, keeps the IP address secret, and, using a cache, speeds up access
to websites that have been visited before
TLS - Transport Layer Security *** this is a form of secure data transmission made up of 2 layers: the
record protocol, and the handshaking protocol. It is very secure and fairly new, and can make use of
session caching, which improves performance. It involves many complicated encryption algorithms.
prevents third party hacking into communication between web server and the user's computer.
session caching *** this is used in TLS to avoid using too much computer time; TLS is able to attempt to
resume an existing session, which increases speed.
Denial of Service (DoS) attack *** attempting to prevent a user from accessing part of a network (usually
the server); this is usually temporary, but may be very damaging, or a big security breach. overloads web
traffic by sending thousands of requests.
free software *** software that is free to run, copy, change or adapt, and share with friends, family or
colleagues.
CSS *** Cascading Style Sheet. Controls presentation of page. Enable multiple pages or elements on a
page to be changed in one go.
Gigabyte (GB) *** 1024 megabytes. 2 to the power of 30 bytes.
HTML *** HyperText Mark-up Language. Used to write and develop webpages to present text. Uses
tags.
Terabyte (TB) *** 1024 gigabytes. 2 to the power of 40 bytes.
Lossless image compression *** Find groups of repeating data. Records the data once and the number
of times it was repeated.
, Lossless text compression *** Finds patterns in original text. Encodes each pattern in a dictionary
PNG *** Lossless picture file format that uses alpha channel to keep transparent backgrounds.
MIDI *** A set of instructions for digital instruments to play synthesised sounds. Musical Instrument
Digital Interface.
.WAV *** uncompressed music files
.FLAC *** lossless compressed music files
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.
1KB (kilobyte) *** 1,024 bytes (2¹⁰ bits)
1MB (megabyte) *** (2²⁰ bits)
1GB (gigabyte) *** (2³⁰ bits)
1TB (terabyte) *** (2⁴⁰ bits)
1PB (petabyte) *** (2⁵⁰ bits)
A *** 10
