Technical information

ICT in the science department 1646 © CLEAPSS 2005
Clock (System clock). This refers to the computer’s internal clock, the speed of which
determines the rate at which information and commands are processed.
CMOS Complementary Metal Oxide Semiconductor: a chip that uses less power than equivalent
conventional ones. Used as the sensing chip in some cameras as an alternative to a CCD
sensor.
C-mount The industry standard screw thread mounting that attaches a lens to the body of a SLR
camera. Any C-mount lens or accessory can therefore be screwed onto a C-mount-
compatible camera.
CMS Colour Management System. A technology designed to calibrate and match image
colours on a display with those of the image in printed form.
CMYK Cyan Magenta Yellow blacK. A colour model for full-colour print or display, made up of
the four stated colours.
Codec Compressor / decompressor: Software or possibly hardware that can compress and
decompress audio or video data.
Command A word or phrase that a computer program recognises as an instruction to carry out some
action.
Constant In a computer program, a named data store, the value of which does not change during
processing.
Component
video
The recording and transmission of video in which signals are maintained in separate
channels. By contrast, composite video mixes all signals in one channel. The term
typically refers to component analogue video (YPbPr) but it may also refer to component
digital video (YCbCr) or, sometimes, analogue / digital RGB.
S-video (Y/C video) is called component video but S-video combines the two colour
difference signals (B-Y and R-Y) whereas component video keeps them entirely separate.
Component video usually provides a higher-quality video than composite video systems.
See YPbPr.
Composite
video
Video signals in which the separate RGB, chrominance and luminance signals are
transported together via a single channel. Composite video provides lower-quality video
than component video systems. See RCA.
Compression Minimising the size of a file to reduce the space it takes up in storage and the time it
would take to transmit its contents to another digital device.
Contrast ratio The measurement of the difference in light intensity between the brightest white and the
darkest black generated by a display screen. A higher ratio indicates a better display.
Control signal A signal used to command a device or process.
Cookie A data file that a web server stores on the client computer. Typically contains information
identifying the user so that the web server can serve pages customised to your
preferences.
Corrupt Data that has had errors introduced either by hardware fault, error in transmission or
damage / failure of the storage medium.
CPU Central Processing Unit: the computational and control unit of a computer. Typically
housed on a single chip called the microprocessor.
Crash / lock up Describes a computer system or program that fails or grinds to a halt.
Cross platform Applications, formats or devices that are compatible with more than one platform and
operating system, for example, PC and Mac computer systems.
CRT Cathode Ray Tube. Traditional TV and computer monitors have CRT screens.
CSV Comma-Separated Values. A file extension for a text file containing tabulated data in
which individual entries are separated by commas.
D/A converter A circuit to convert a digital signal to analogue.
Daisy chain To connect a set of devices in a series like a daisy chain. For instance, on a Macintosh
computer, the mouse connects to the keyboard and that then connects to the computer.
Data Pieces of information.
Data bus A bus across which information is transferred between the processor and memory.