Glossary of PC terms: C

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Cache memory	Specialized RAM used to optimize data transfers between system elements with different performance characteristics, e.g., disk to main memory or main memory to CPU. Having certain data stored in cache speeds up the operation of the computer. There are two kinds of cache: internal (or memory cache) and external (or disk cache). Internal cache is built into the CPU, and external cache is on the motherboard. When an item is called for, the computer first checks the internal cache, then the external cache, and finally the slower main storage.
CAV	Constant Angular Velocity
Cluster	A group of sectors on a hard disk drive that is addressed as one logical unit by the operating system. It is also the smallest contiguous area that can be allocated for the storage of data even if the actual data require less storage.
CLV	Constant Linear Velocity
CMOS  (Complementary Metal Oxide Semiconductor)	A memory chip which keeps a data record of the components installed in a computer. The CMOS uses the power of a small battery and retains data even when the computer is turned off.  CMOS is used by a computer to store PC's configuration settings, such as date, time, boot sequence, drive (s) parameters, etc.
Controller	Printed on a drive or plugged-in circuit board which deals with all drive operations (read, write, access, load-unload, etc.) and communicates with the operating system.
Coercivity (Hc)	Coercivity is a measure of the magnetic field that is needed to reduce magnetization in a thin-film layer to zero. A material's coercivity corresponds to its magnetic strength. The measure for coercivity is an Oersted (Oe). See also Remnant magnetization.
CPU	Central Processing Unit or just Processor.  CPU is on a single chip that performs arithmetic and logical operations, decodes and executes instructions.
Control Transfer	A transfer of data from the host computer to a USB device to provide it with configuration and control information.
Control Redundancy Check (CRC)	Used to detect error in the transmission of data. The CRC is transmitted along with the data packets for comparison with a CRC calculated by the receiving device.
CSS	Contact Start-Stop technology (see also Load-Unload). The idea of CSS is that when the drive is turned of and the slider is not flying, it lands on a specially prepared (in the new drives - laser textured) landing zone where it rests until the next power-on cycle.  A durability of CSS drives is usually measured in CSS cycles (landing - take-off cycles). Newest mobile and server drives use different technology called Load-Unload (L/U), where the slider is parked on a special ramp when the drive is turned off.
Cylinder	A group of tracks with the same radius in an assembly of hard disk platters.

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