Glossary C & D

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• Cache: (pronounced cash)

  Is a special temporary high-speed storage area, where frequently accessed data can be stored for rapid access. It is either a reserved section of the main memory (memory cache) or an independent high-speed storage device (disk cache).

  L1, or primary cache, is a small, high-speed cache incorporated right into the microprocessor chip. It typically ranges in size from 8KB to 64KB.

  L2, or secondary cache, is memory between RAM and the CPU. Typically 64KB to 2MB in size and uses high speed static RAM.

  L3, is high-speed memory built into the computer's motherboard, between the CPU and the main memory.

  CGI: (Common Gateway Interface)

  Is a standard for passing data between a server and an applications as part of the WWW's HTTP protocol. It is a consistent way for information to be passed from the Web server to an application and back again.

  Client:

  A computer that retrieves information from or uses resources provided by the server computer.

  Or, a client is a program or task that calls upon a service provided by another program.

  Cluster:

  The smallest quantity of storage on a disk drive.

  When a disk is formatted it is divided into concentric tracks, each of which is divided into segments, known as sectors (512 bytes of data). Windows XP NTFS file system uses a cluster size of 8 sectors (4096 bytes of data).

  Codec: (coder/decoder)

  It is an algorithm used to compress files that would take up an excessive amount of disk space or that would take a long time to transmit over the Internet. At the receiving end the compressed data is passed through another codec to decompress the data into a usable format. They are most frequently used on multimedia files (music and video).

  Commit Charge:

  Is a Windows operating system term, to describe the total amount of virtual memory usage (pagefile).

  It is indicated by Total, Limit and Peak amounts, as outlined in the Task Manager.

  - Total: This indicates the current amount of virtual memory (the pagefile) being used by applications and system processes.

  The amount is a combination of physical memory (RAM) and the size of the pagefile being used.

  The PF Usage graph reflects not only the pagefile contents but the amount of RAM (physical memory)used, the total commit charge.

  
  - Limit: It is the maximum possible total value.

  It is the sum of the current pagefile size plus the physical memory (RAM) available for paging (excludes RAM assigned to non-pageable areas).

  
  - Peak: The highest the Total Commit Charge has reached since the computer was last booted.

  Cookies:

  Are parcels of text sent by a web server to a web browser and then sent back unchanged by the browser each time it accesses that server.

  They are used for authentication, tracking and maintaining specific information about a user.

  Cookies are simple pieces of data, unable to perform any operation by themselves. They are neither spyware nor viruses.

  Data word:

  Generally a word is 16 bits, or 2 bytes.
  A 32 bit data word is termed a double word.

  Device Driver:

  A device is a hardware unit that extends or assists the existence of the computer in some way.

  Most devices connected to a system don't speak the same language as the computer. Device drivers (just drivers), are programs that act as translators between the device and the application (program) using the device. Drivers can translate information from or to a device.

  Typically the driver will have the extension .sys with associated .dll files.

  Double word:

  32 bits per data word.

  DHCP (Dynamic Host Configuration Protocol):

  A method of automatically assigning IP addresses to all Internet connected nodes of a network.

  DNS (Domain Name System):

  Is an Internet service that translates domain names into IP addresses.
  Domain names are alphabetic and IP addresses are numeric
  (eg. 139.427.23.286).

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