Download Glossary of Terms

GLOSSARY
IT 318 PACKET
An Excellence Project by Ed Packer, Fall 2007; expanded by Alcides de Souza, Winter
2011
AC (Alternating Current): Electric current that changes polarity or direction.
Source: pg 37 of text
BIOS: The Basic Input/Output System (BIOS) refers to a chip in some types of microcomputers,
especially those that use Microsoft operating systems. The BIOS, which can be thought of as an extension
of the operating system, holds information about attached devices such as disk drives, external buses, etc.
The BIOS also helps systems boot up.
Source: pg 4 of text
Booting: Computers are described as booting up after the observation of early designers that the system
should “pull itself up by its bootstraps.”
Source: pg 4 of text
Bus: A bus is a pathway that carries information between two or more parts of a computer. There are
internal buses, such as the system (memory) and I/O buses, and external buses, such as USB or FireWire.
Source: pg 7 of text
Capacitance: The ability to store charge in an arrangement of two plates with a difference of potential
between them. Measured in farads (F).
Source: pg 46 of text
Capacitive Reactance: The opposition to AC current provided by a capacitor; it opposes changes in
voltage, and causes a phase shift of -90°.
Capacitor: A setup of two conductive plates separated by an insulating material. Depending on the
surface area of the plates and the distance between them an amount of charge will be stored.
Source: pg 46 of text
Circuit: A circuit is a specific path from one point to another in a network.
Source: pg 313 of text
Chipset: The chip set refers to a group of chips that provides an intelligent interface for the core
components of a computer, CPU, Memory, Graphics, I/O System. Also includes the glue logic, which are
chips designed to help the core components talk to each other.
Clock Speed: CPU’s and other devices are controlled by quartz crystal clocks. The consistent time
provided by the clocks helps to keep operations synchronized. Clock speed is usually measured in
millions of cycles per second (MHz) or billions of cycles per second (GHz).
Source: pg 20 of the text
CPU: Central processing unit, is the part of the computer that carries out the actual computation,
arithmetic and logical operations. In the early computers the CPU used many chips but today’s computers
nearly all use microprocessors.
Computer: Electronic instruction executer
Source: Class notes on M14
Current: The flow or movement of charged particles. Current is measured in amperes (A). One ampere
equals one Coulomb of electric charge per second; a Coulomb is 6.24 x 1018 electrons.
Source: pg 5 of text, and Wikipedia (electric current)
DC (Direct Current): Electric current that does not change direction, or polarity as alternating current
does.
Source: pg 36 of text
DRAM: Dynamic Random Access Memory (DRAM) is a type of chip-based storage that has the
advantage of being reasonably fast and inexpensive, but the disadvantage of being volatile-losing its
contents when electrical power is cut off.
Source: pg 7 of text
Decode: one of the four internal operations of a CPU. Once the CPU receives the information it is
turned over to a place in the chip area that decodes the data to decide which of the chip circuits should be
used.
Source: pg 16 of text
Execute: After an instruction is decoded, it is then executed. The part of the CPU that actually executes
the instruction depends on the nature of the instruction.
Source pg 16 of text
FAT: The File Allocation Table (FAT) is a small database kept on a disk. The FAT contains information
about all the files on the disk, including where the various parts of the file are kept. If your FAT gets
messed up, you can lose track of everything on the disk.
Source: pg 42 of text
Fetch: one of the four internal operations of a CPU. First instructions and data are fetched from
outside of the chip, normally from the DRAM.
Source: pg 15 of text
Frequency: The number of cycles of a periodic wave (such as a sine wave) that occur in one second.
Measured in Hertz (Hz).
Source: pg 40 of text
Hub: A hub is a passive network device that simply repeats and rebroadcasts packets or frames.
Source: pg 339 of text
Impedance: The total opposition to current in an electric circuit, consisting of resistance (R), capacitive
reactance (XC), and inductive reactance(XL), combined as vectors. Its symbol is Z.
Inductance: a property of electric circuits that induces a voltage that opposes change in the circuit
current.
Source: pg 44 of text
Inductive Reactance: The opposition to ac current resulting from the inductance of a circuit or coil. It
opposes changes in current, and causes a phase shift of +90°.
Source: pg 44 of text
Kirchhoff’s current law: Law that states that the sum of the current entering and the sum of the current
leaving a junction are equal.
Source: pg 14 of the text
Kirchhoff’s voltage law: Law that states that the sum of the voltage drops around a circuit equals the
total voltage provided from the source.
Source: pg 14 of the text
Logic gate: A logic gate is a series of transistors connected in a way that allows it to carry out
mathematical or logical operation such as addition. Logic gates are grouped into electrical circuits that
execute the CPU’s instructions such as to “add” two numbers or “compare” two values.
Source: pg 16 of text
Modulation: The process of modifying a wave so that it can carry information is known as modulation.
There are three ways of modulating a wave: changing its amplitude, frequency, or phase.
Source: pg 270 of text
Moore’s Law: Intel pioneer Gordon Moore stated that the number of transistors on a chip would double
every eighteen months, and that their cost would fall by fifty percent during the same time.
Source: pg 22 of text
Ohm’s Law: Ohm’s Law states that “current is directly proportional to the applied voltage and inversely
proportional to the resistance of the circuit.” (I=V/R)
Source: pg 7 of text
Parallel circuit: An electrical circuit in which different branches exist, allowing the same amount of
voltage across each branch, but different amounts of current.
Peak Value: The value of the peak of a sine wave representing voltage or the largest instantaneous value
of voltage. The peak value is equal to ½ the peak-to-peak value, and 1.414 (or √2) times the RMS value.
Source: pg 38 of text
Potentiometer: A small device that varies the amount of resistance in a circuit by moving an adjustable
wiper that slides an electrical contact along a resistive element. Thus a potentiometer allows voltage
adjustment.
Source: pg 10 of text
Power: The rate that electrical energy is used or transferred. Power is measured in Watts (W), which is
directly equivalent to joules per second; that is, 1W = 1 Joule/sec.
Source: pg 19 in text, Wikipedia (electric power)
Register: Is a CPU storage space where instructions and data can be transferred and held temporarily for
fast retrieval.
Source: pg 17 of text
Resistance: The property of a material that opposes current flow. Resistance is measured in Ohms (Ω)
Resistor: A small electronic component used in circuits to limit the amount of current passing, or to drop
a certain amount of voltage. Resistors allow control of amperage and voltage levels in a circuit.
Resonance: A particular frequency in a series LC circuit at which the current has its highest amplitude. It
is characterized by the fact that XC=XL (so they cancel each other) and the total impedance (Z) = the
resistance of the circuit, and the phase shift =0°.
RMS Value: Root mean square of the peak voltage, or .707 (or 1/√2) times the peak value.
Source: pg 38 of text
Series circuits: An electrical circuit in which the components (resistors, capacitors and/or inductors) are
arranged in the same branch, so that the same amount of current flows through each, but with different
amounts of voltage drop.
Source: pg 8 of text
Superscalar: a CPU that is superscalar mean that is has more than one pipeline.
Source: pg 25 of the text
Store: Instructions not only have to tell the CPU what operation to perform but also where to put the
results.
Source: pg 17 of text
Trace: The wires that connect devices within a chip are so tiny that they are called traces.
Source: pg 22 of text
Transformer: An arrangement of two or more coils in proximity to each other so that an ac voltage
applied to one will induce a voltage in the other(s). Transformers are used to step up or down voltage (and
conversely to step current down or up), to provide DC isolation, or to provide impedance matching.
Source: pg 49 of text
Voltage: The difference of the electrical potential across a circuit. The electrical potential is the force that
causes electrons to flow. Voltage is measured in volts (V).
Source: pg 7 of text, Wikipedia (voltage)
Watts: The SI unit of power. One watt equals 1 Joule per second.
Source: pg 20 of text
Wait state: A wait state occurs when the CPU has to wait for the system to fetch the next instruction or
data that is needed. Unfortunately, much of the time a CPU is in this wait state, since memory cannot
keep up with the speed of the CPU.
Source: pg 45 of text
Word: A computer word length is the amount of information that it can process at one time. Current
desktop computers use 32-bit words and 64-bit words.
Source: pg 23 of text