Michael Henson's

Glossary of Computer Science Terms

Index | A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


packet: a component of a message consisting of a sequence of data elements of restricted length together with addressing information
packet switch: a special-purpose computer that is dedicated to the task of sending and receiving data on the behalf of other computers in a WAN
packet switching exchange (PSE): See packet switch.
parameter: a value passed as input to a subroutine
parity bit: a bit which is automatically set or cleared each machine cycle in order to maintain an even number of 1-bits, such that the count of 1-bits in the accumulator plus the parity bit equals an even number; the eighth bit in the PSW register
partition: a subsystem that provides a particular kind of service. A partition may itself be built from lower level subsystems.
peer: two or more system components that are mutually interdependent for services.
performance transparency: a type of transparency that allows the system to be reconfigured to improve performance as loads vary.
policy: the making of context-dependent decisions
polymorphic: "takes on many forms"; the ability of an object to have many identities based on inheritance, interfaces, and overloaded methods; the property that an operation may behave differently on different classes
port: a software-definable destination point for communication within a host computer
primary copy model: a replication model in which all front ends communicate with the same primary server when updating a data item
prime number: an integer whose only factors are 1 and itself
principal: an agent accessing the resources held in a distributed system
private member: a variable or function that can only be accessed from within the same class
process: (in a DFD) something that transforms data values.
process group: a construct that enables a number of concurrent processes to cooperate by sharing a single communication mechanism
processor pool model: a modification of the workstation-server model in which processors can be dynamically allocated to user tasks for the lifetime of the process
program counter: a register in the CPU that serves as a pointer to the next instruction in memory to be executed
program status word register (PSW): the flag register; an 8-bit register which indicates a variety of arithmetic conditions
propagation: the automatic application of an operation to selected objects in a network when the operation is applied to some starting object in the network
proper fraction: a fraction in which the numerator is less than the denominator
protected member: a variable or function that can only be accessed by classes in the same package or by subclasses
protocol: a well-known set of rules and formats to be used for communication; specification of the semantics of an operation
protocol layer: a layer of the network software hierarchy
protocol stack: See protocol suite.
protocol suite: a complete set of protocol layers
PSE: Packet Switching Exchange
See packet switch.
public member: a variable or function that can be accessed by all objects