Glossary 529
time and then switches to the execution of the next
program, the environment is known as multi-pro-
gramming, which it handles by the operating system.
Multi-tasking Switching from one task to an-
other and attending each task for a small amount
of time.
Nibble Group of four bits.
Noise Unwanted electrical disturbance during
signal transmission.
Non–pre-emptive scheduling Allowing a se-
lected process to complete its execution till its
stipulated time.
Non-vectored interrupt An interrupt without
any pre-assigned branching address.
Object code Translated program in machine
code, without linking.
Octal Number system with base as eight.
One’s complement Inversion of present state of
any binary representation.
Opcode Binary representation of processor in-
struction.
Operand Entities using which an operation is
completed.
Operand fetch Getting an operand from exter-
nal memory prior to an operation with it.
Operating system A software that interacts bet-
ween the system hardware and the user or user pro-
gram.
Optical disc A circular, thin and at storage
media capable of storing binary data in form of pits
and land. The pits or depressions are created by la-
ser beam and have poor light re ection capability
with respect to that of land (non-pit) area, A pit rep-
resents logic low and a land represents logic high.
Optical drive The drive used for optical discs.
Orthogonal Perpendicular.
Overlays Using same main memory area for
two separate program segments to be executed in
order of loading them one at a time and managed
by the software itself.
Packet Selected bunch of binary data with pre-
assigned number of bytes for transmission through
a network.
Page Imaginary division of primary and sec-
ondary memory into smaller and uniform parts for
economy in main memory usage.
Paging Using the page divisions of memory.
Parallel Providing path for simultaneous opera-
tion or ow of current.
Parallel processing Execution of more than one
instruction concurrently by a processor using mul-
tiple ALU and pipeline architecture.
Parent node Root node or previous or higher
level node with respect to child node.
Parity Number of 1s in a byte or word. Ex-
pressed as either even or odd.
Pen drive A small device with USB interface
and internal memory capable of storing several
GB of data.
Pentium Name of processor series from Intel
introduced after 80486.
Physical address Location in physical memory.
Pipeline Subdividing and implementing pro-
cessor operations into different smaller and inde-
pendent stages so that multiple stages of different
instructions may be executed at the same cycle in
parallel.
Pits Depressions within the media-track of op-
tical discs. The intensity of re ected light beam
becomes less and designated as logical zero.
Pixel The smallest area within CRT screen that may
be independently illuminated by the electronic gun.
Plasma Fourth state of matter.
Platters Magnetic media discs of hard disc
drive.
Post-decrement Decrement of last used address
by one after its usage.
Postulates Basic rules of Boolean algebra
Power management Re-arranging certain sig-
nals so that the processor consume optimum power
at different states.
Power-on reset Initializing the processor after
switching its power on.
Preemptive scheduling Terminating a selected
process before completion of its execution till its
stipulated time to allow some other process to
avail processor time.
Primary cache On-chip cache closest to the
processor.
Princeton architecture It does not distinguish
between program memory and data memory. Also
known as Von Neumann architecture.
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530 Computer Architecture and Organization
Printer Output device to produce hard copies.
Process A program or its segment being or about
to be executed.
Process switching Terminating the ongoing pro-
cess and allowing the next process to have CPU
time.
Processor Same as microprocessor.
Program-lock Not allowing unwanted access to
program memory of a processor.
Programmed I/O Non-interrupt driven I/O. The
processor is to wait for a valid input in such case.
Pull-up resistor External or internal resistor be-
tween Vcc and the desired input or output so that
the default state is always logic high.
Punched card Cards perforated by machine at
prede ned locations to input data for old comput-
ers through card reader.
Purge To delete or abort (before time).
Queue One dimensional array.
QWERT keyboard The widely used layout of a
keyboard. Its top-left set of English alphabet that
are QWERT.
Real-time system A system to react within stip-
ulated time.
Reboot Re-initializing the computer.
Register An array of ip- ops to store data
within processor.
Register array File of registers.
Register fi le Same as register array.
Register oriented processor Processor offering
adequate number of internal registers to store oper-
and and results of operations so that memory com-
munication is minimized.
Register-to-register architecture Where all
registers are capable of storing the result of ALU
operations instead of an accumulator for that
purpose.
Relay An electro-mechanical or solid-state de-
vice to boost voltage (or current).
Repeat-until A program loop structure where
terminating condition is checked at the end of the
loop-body.
Reserved words Words that may not be selected
to be used within a program as they are intended to
serve some other purpose.
Resolution Size of shortest division.
Return address The address of next executable
instruction before departure to call a procedure.
Routing Directing data packets to appropriate
places in data communication network.
Scanner An electronic device to generate the
bit-mapped image of a document.
Scheduler The program segment of an operat-
ing system to schedule processes.
Scheduling To decide the order of execution of
processes in a queue.
Scratch-pad General purpose storage registers
of a processor.
Secondary cache On-chip or off-chip cache
next from primary cache of the processor.
Semaphore Indication by the procedure to allow
only one process to use a shared data set by entering
within the critical section.
Sequential circuit Circuit, driven by clock
pulses whose output is time-dependent.
Serial One at a time, generally bit-wise.
Signed magnitude A method of representing
signed numbers in binary format with its sign-
representing bit as the most signi cant bit.
Simplex One way communication technique.
Single step Execution of only one instruction at
a time.
Sleep-mode Power saving mode of processor
when its internal clock is temporarily stopped.
Smart card RFID-based card
Software interrupt Interrupt evoked not by ex-
ternal hardware signal but through internal soft-
ware command.
Solar cell Photo-voltaic cell to generate electri-
cal voltage/current from solar energy.
Source code The code to be translated to ma-
chine language for its execution.
Split cache Separate caches to accommodate in-
struction and data.
Stack Array of RAM locations pointed by Stack
Pointer to accommodate return addresses and oth-
er information in LIFO basis.
Stack pointer Processor register to have the lat-
est used (or next to be used) address of the stack-
top.
Stack-top Last saved or next to be saved loca-
tion of the stack.
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Glossary 531
Stalling Inability of processor to execute a stage
of its pipeline execution stages.
Start-bit First bit (generally low) indicating
starting of a byte transmission being followed in
case of serial data transfer.
Static RAM Flip- op based electronic circuit to
store binary information as long as the power is
applied.
Status register The register of a processor to re-
ect the status of result of any arithmetic or Bool-
ean operation of the ALU.
Stop-bit Last bit(s), generally high, to indicate
the completion of transmission of a byte of infor-
mation in case of serial communication.
Structural hazard It occurs when two separate
instructions try to share the same hardware source
in pipeline con guration.
Subroutine A program segment terminated by a
return instruction, so that it may be used multiple
times at different parts of a program.
Super-computer see Main frame.
Super-scalar operation Execution of multiple
instructions simultaneously by the processor.
Super-scalar processor A processor capable of
superscalar operation.
Swapping Inter-changing places of two pro-
grams located at disc and main memory.
Synchronous Information transfer between two
devices running under the supervision of the same
system clock.
System programming Program development
with instructions capable of directly interacting
with processor architecture, generally in assembly
language or C.
TAG-RAM Cache directory.
Talker A device interconnected through
IEEE488 bus assigned to send signals.
Thrashing Repeated cache-miss
Thread A light weight process with own program
counter and stack pointer values and own register
set but sharing the program code with the process.
Timer An electronic device with programmable
internal counter to generate interrupt at its termi-
nal count.
Timing diagram Graphical representation of
change in signal amplitude patterns
Toggle Interchange of binary states.
Touch pad Electronic sensor capable of produc-
ing proportionate electrical signal with change in
applied pressure.
Transistor The electronic device invented at
Bell Laboratories implementing the function of a
switch.
Tri-state/(3-state) Invented by National Semi-
conductors to generate a high-impedance state
apart from on-state and off-state for digital
logic.
Tri-state buffer An electronic current boosting
device offering 3-state output.
Truth table Tabular representation of various
combinations of input and output for logic circuits.
T-state The smallest time duration for any in-
struction cycle to indicate any change of signals,
generally a function of system clock frequency.
Two’s complement One’s complement incre-
mented by one.
Unifi ed cache Same cache to accommodate
both instruction as well as data.
Universal gates NAND and NOR logic gates.
Function of all other type gates may be imple-
mented by either of these two gates.
Vacuum tube An electronic device of early
days capable of acting as a diode or as a transistor.
Vectored interrupt An interrupt with a pre-as-
signed branching address.
Virtual memory Non-existent physical memory
available only for the program developer.
Von Neumann architecture Pronounced as
Fon Neumann architecture. See Princeton archi-
tecture.
Wafer Very thin silicon based miniature elec-
tronic circuit.
Wait-state Processor state without any func-
tion.
Watchdog reset Reset generated by watchdog
timer.
Watchdog timer A timer that generates a sys-
tem reset if its counter is not reloded before its
terminal count.
While-do A program loop structure where ter-
minating condition is checked at the beginning of
the loop-body.
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532 Computer Architecture and Organization
Windows Operating system from Microsoft.
Word Group of bytes, generally indicating the
width of data bus of the processor.
Workstation A computer with assignable disc
space and more memory and computing power
with better resolution display.
Worst fi t Selection of a vacant memory slot for a
program so that maximum memory area is wasted
(left vacant).
Write-back The method of updating the main
memory for a changed data at a later stage after up-
dating the cache immediately.
Write through The method of updating the
main memory and cache simultaneously for a
changed data.
X-Y plotter An output device capable of produc-
ing hard copies of drawings or gures through vec-
tor commands from the host.
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