Data Center Industry Terms
D
- DAC
- Discretionary Access Control. Provides detailed access control on files and resources.
- DAT
- Digital Audio Tape. Originally developed for audio recording.
- Data Center
- The department that houses the computer systems and related equipment, including the data library. Data Entry and systems programming may also come under its jurisdiction. A control center is usually provided that accepts work from and releases output to user department.
- Data mining
- Generic term for identifying possible relationships and trends between data items. Typically data mining is the statistical analysis of data to identify commonalities and patterns.
- Database Connectivity
- Connecting and communicating between an application and a database system.
- DDK
- Device Driver Kit. Normally used to refer to the Microsoft Windows Driver Development Kit.
- Dehumidification
- The process of removing moisture from air. In the data center or IT room, most dehumidification occurs as moisture-laden air flows across the cold evaporator coil. I basic example of the dehumidification process is when a cold soda can is left outdoors. The water moisture in the air is removed by condensing on the surface of the can as water droplets.
- Denial of Service
- Denial of Service is an attack on a system (typically a server or a network) that aims to crash, block or overload the system and thereby deny its services to others. A denial of service attack is illegal in most countries.
- Design Condition
- The desired properties for an environment expressed in dry bulb temperature, wet bulb temperature and relative humidity. Design conditions are commonly used during the planning stages of a data center or IT room as a basis to aid in the specification of air conditioning systems. Cooling equipment manufacturers normally published performance data of air conditioning systems at several design conditions.
- Dew Point (DP)
- The temperature at which water vapor begins to condense. On a hot summer day, a cold soda can is below the dew point which causes condensation on the surface of the can.
- DFM
- Design For Manufacturing.
- DFS
- Distributed File System. Simplifies the process of creating a single directory hierarchy that includes multiple file servers and shared folders in a group, division or enterprise.
- DHCP
- Dynamic Host Configuration Protocol. Communications protocol where a range of IP addresses are managed centrally and assigned automatically to computers on demand. The alternative is to use static IP address where each computer is permanently allocated a fixed IP address.
- Direct Current
- Electrical current which flows consistently in one direction.
- Direct Expansion Systems (DX)
- A general term applied to computer room air conditioning systems that have a self-contained refrigeration system and are air, glycol, or water-cooled.
- Discharge
- In batteries, it is the conversion of chemical energy into electrical energy within a battery cell.
- Discharge Rate
- In batteries, it is the rate in Amperes (or Watts), at which current (or power) is delivered by the battery. The discharge rate must always be referenced back to an end of discharge voltage.
- Disk Thrashing
- On a system with Virtual Memory, pages of memory are read from and written to the swap file as necessary. Disk Thrashing is when there is excessive paging, specifically when the I/O system is busy paging memory but the CPU is not fully utilized - generally if the system is unresponsive (i.e. slow) and there is lots of disk activity then the system is likely to be thrashing.
If disk thrashing is a problem then a short term solution may be to reduce the number of running applications. A longer term solution is to add more memory. Dis
- DLT
- Digital Linear Tape. Tape storage developed in the late seventies by Digital Equipment Company, and the basis for successive generations of DLT tape drive which higher storage capacities and transfer rates. Most DLT drives are backwards compatible but check. DLT tapes use half inch tape media, fully enclosed in a sealed case which is designed only to open when the tape is in the drive.
- Down Flow
- A term applied to computer room air conditioners and air handlers that discharge air in a downward direction. Typically used to feed air to a raised floor, but also can distribute air at floor level if the air conditioner is placed on an elevating stand.
- DPC
- Data Processing Center
- Dry Bulb Temperature
- The temperature of air shown on a standard thermometer.
- Dry Charge (Battery)
- The process by which the electrodes are formed and assembled in a charged state. The cell or battery is activated when electrolyte is added.
- Dry-type transformer
- Transformers that use only dry-type materials for insulation. These have no oils or cooling fluids and rely on the circulation of air about the coils to provide necessary cooling. Such units are usually limited in size to a few hundred kVA because of problems of cooling the larger units.
