primary cache

<hardware, architecture>

(L1 cache, level one cache) A small, fast cache memory inside or close to the CPU chip.

For example, an Intel 80486 has an eight-kilobyte on-chip cache, and most Pentiums have a 16-KB on-chip level one cache that consists of an 8-KB instruction cache and an 8-KB data cache.

The larger, slower secondary cache is normally connected to the CPU via its external bus.

Last updated: 1997-06-25

Primary Domain Controller


(PDC) Each Windows NT domain has a Primary Domain Controller and zero or more Backup Domain Controllers. The PDC holds the SAM database and authenticates access requests from workstations and servers in the domain.

Last updated: 2003-07-16

primary key


A unique identifier, often an integer, that labels a certain row in a table of a relational database.

When this value occurs in other tables as a reference to a particular row in the first table it is called a "foreign key".

Some RDBMSes can generate a new unique identifier each time a new row is inserted, others merely allow a column to be constrained to contain unique values.

A table may have multiple candidate keys, from which the primary key is chosen. The primary key should be an arbitrary value, such as an autoincrementing integer. This avoids dependence on uniqueness, permanence and format of existing columns with real-world meaning (e.g. a person's name) or other external identifier (e.g. social security number).

There should be enough possible primary key values to cater for the current and expected number of rows, bearing in mind that a wider column will generally be slower to process.

Last updated: 2006-05-29

primary management domain


(PRMD) The component of an X.400 electronic mail address that gives the organisation name, usually abbreviated to p= in written addresses.

See also ADMD.

Last updated: 2003-05-15

Primary Rate Interface

(PRI) A type of ISDN connection. In North America and Japan, this consists of 24 channels, usually divided into 23 B channels and 1 D channel, and runs over the same physical interface as T1. Elsewhere the PRI has 31 user channels, usually divided into 30 B channels and 1 D channel and is based on the E1 interface.

PRI is typically used for connections such as one between a PBX (private branch exchange, a telephone exchange operated by the customer of a telephone company) and a CO (central office, of the telephone company) or IXC (inter exchange carrier, a long distance telephone company).

Last updated: 1995-01-18

primary storage

main memory

Nearby terms:

preventive maintenancePRIprimary cachePrimary Domain Controllerprimary key

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