Terminology
Boot
The process that takes place when a PC is turned on and performs the routines
necessary to get all the components functioning properly and then loads the
operating
system.
Bus
Millions of bits of information are
constantly flashing among the components of the PC even when it appears to be
simply sitting there. The bus is the highway system for all this data. The bus
transports data among the processor and other components. There is no single
component you can point to and say that this is the bus. The bus is a complex
conglomeration of electrical circuits that permeate the PC. Bus speed is
measured in bits - typically either 16 or 32. This is the size of the word that
can be moved along the path.
CD ROM Drive
Uses a laser beam to read data from a spiral
of indentations and flat areas on a layer of a compact disc, similar to musical
compact discs.
CD ROM-DVD Drive
Similar to CD ROM Drive except that the data
is more compact and stored on more than one layer of the disc giving it a
storage capacity much larger.
Circuit Board
Most of the components of a computer are
mounted on a circuit board of which the motherboard is the largest. Expansion
cards and memory chips plug into the motherboard ganged together on small
circuit boards to create single in-line memory modules or SIMMS.
Clock
A microchip that regulates the timing and
speed of all the computers functions. The chip includes a crystal that vibrates
at a certain frequency when electricity is applied to it. The shortest length of
time in which a computer can perform some operation is one vibration of the
clock chip. The speed of clocks, and therefore computers, is expressed in
megahertz.
CMOS
Stands for Complementary Metal Oxide
Semiconductor. The CMOS, powered by a small battery, chip retains crucial
information about what hardware a PC comprises even when power is turned off.
CPU
Stands for Central Processing Unit. This is a
microchip that processes information and the code instructions used by the
computer. It is the brains of the computer. It consists of a controller (traffic
cop), registers (computers fastest memory), and the arithmetic logic unit or
ALU. The ALU is the number cruncher.
Daughterboard
See motherboard below.
Floppy Drive
Name come from the past when the discs could
be easily bent. It takes a 3.5 inch disc that contains 1.44 MB of data.
Hard Drive
A mechanism in a computer used to store
data. Before it is processed, it is moved to main memory and then to the
registers of the CPU as needed. This memory is slower than RAM but it
remains when the PC is turned off. It consists of spinning disk (s) in the
computer that is accessed with read-write heads. The capacity of a hard drive is
usually measured in megabytes or gigabytes. As of this writing, the minimum on
new computers is around 20 gigabytes.
A sealed metal housing protects the
components A cutaway showing the major components inside the metal housing is
also shown here.
A printed circuit board is located at the
bottom of the drive. This board, also known as a logic board, receives commands
from the drive's controller, which in turn is controlled by the operating
system. The logic board translates those commands into voltage fluctuations that
force the head actuator to move the read/write heads across the platters'
surfaces.
A spindle connected to an electrical
motor spins as many as eight magnetically coated platters at several thousand
rotations per minute. The number of platters and the composition of the magnetic
material coating them determines the capacity of the drive.
Read/write heads, attached to the ends of
the moving arms, move in unison across the surface of the hard drive's spinning
platters. The heads write the data coming from the disk controller to the
platters by aligning magnetic particles on the surface of the platters. The
heads read data by detecting the polarities of particles that have already been
aligned.
The system keeps track of where data is
stored by consulting and writing to a file allocation table or FAT. A single
file may be stored in many non-contiguous locations.
IDE Controllers
A computer usually has two IDE slots built
into the motherboard. They provide connections for ribbon cables that send
signals controlling the floppy drive, hard drive, and CD-ROM drives.
Interrupts
Some hardware events, such as a keystroke,
coming through a serial or parallel port need an immediate response from the
processor. These are handled by a signal called an interrupt. They cause the
operating system to temporarily stop what it is doing and divert its attention
to the service required by the interrupt signal.
Keyboard
The processor continuously scans for
signals being sent from the keys. The signal is generated when the user presses
a key an a circuit is closed as shown here in a cut away depiction of the base
of a key.
Depending upon the key being pressed, the
processor interprets the signal as one of the recognizable numbers, symbols, or
characters that is within its vocabulary. The representation is contained a an
internationally recognized table called the American Standard Code for
Information Interchange or ASCII table or code.
Microprocessor
The brains of the computer. It is a tight,
complex collection of transistors arranged so that they can be used to
manipulate data. Most computer operations are handled by the processor and the
design of the processor dictates how software must be written to work correctly
with the computer.
Modem
Stands for Modulate Demodulate. It converts
the digital information of the computer to analog information required by most
phone lines. It is used to connect to the Internet, for example.
Monitor
The screen is controlled by a video
adapter and displays the contents of special video memory in the adapter,
typically called VRAM. VRAM is addressable by the CPU and may contain codes,
colors and attributes of characters, or colors and intensities of individual
pixels (picture elements) when running in graphics mode.
Digital signals from the operating
environment or application software are received by the variable graphics array
(VGA) adapter. The adapter runs the signals through a digital to analog
converter or DAC. Usually, three DACS are included, one of each of the primary
colors (red, green, and blue). The DAC compares the signal to those in a look up
table that contains the matching voltage levels for the three primary colors.
The adapter then sends signals to three
electron guns located in the back of the monitor's cathode ray tube or CRT that
focuses and aims the electron beams.
The beams pass through holes in a metal
plate called a shadow mask. The purpose of this mask is to keep the beams
precisely aligned with their targets on the CRT screen. The CRT's dot pitch is
the measurement of how close the holes are to each other. A smaller dot pitch
means the holes are closer to each other. This in turn means a sharper image.
The electrons strike the phosphors
coating the inside of the screen. The phosphors are materials that glow when
struck by electrons. Three different phosphors are used - one sensitive to each
of the three primary colors mentioned above. To create different colors, the
intensity of each of the three colors is varied. After a beam leaves a phosphor
dot, the phosphor continues to glow briefly. This condition is called
persistence. In order for an image to remain stable, the phosphors must be
reactivated by repeated scans of the electron beams.
Motherboard
This is a sheet of plastic onto which
metallic circuits have been printed and to which slots for other components wait
to receive daughter boards, smaller circuit boards that add to the motherboard
capabilities
Operating System
This software exists to control the
operations of hardware. Essentially, the operating system directs any operation,
such as writing data to memory or to disk, and regulates the use of hardware
among several application programs that are running at the same time. This frees
program developers from having to write their own code for these most basic
operations. Examples are Windows 3.1, 95, 98, Me, 2000, NT, and XP
OCX Controls
Short for OLE custom control. It is a software module based on OLE and COM
technologies that, when called by an application, produces a control that adds
some desired feature to the application. OCX technology is portable across
platforms, works on both 16-bit and 32-bit operating systems, and can be used
with many applications. It is the successor to VBX (Visual Basic Custom Control)
which supported only Visual Basic applications. OCXs have been superseded by
ActiveX controls, which are much smaller and therefore work much better over the
Internet.
Parallel Port
The parallel port is most often used to
connect a printer which requires a high throughput of data.
PCI Expansion Slot
Stands for Peripheral Component Interconnect.
They are designed for cards that use Plug and Play, a hardware design that lets
the cards adapt to the PC automatically.
RAM
Stands for Random Access Memory. This is
memory or disks that can be both read and written to. Random access memory
is really a misnomer because even ROM can be accessed randomly. The term
originally applied to tape storage devices.
Reading from RAM
When
software wants to read data stored in RAM, another electrical pulse is sent
along the address line, once again closing the transistors connected to it.
Everywhere along the address line where there is a capacitor holding a charge,
the capacitor will discharge through the circuit created by the closed
transistors, sending electrical pulses along the data lines. The software
recognizes which data lines the pulses come from and interprets each pulse as a
1, and any line along which a pulse is not sent as a 0.
ROM
Stand for Read Only Memory. These are memory
chips or data stored on disks that can be read by the computer's processor. The
PC cannot write new data to RAM chips or disk drives. The term originally
was used to distinguish RAM from data and software that was stored on magnetic
tape, and which could be accessed only sequentially.
Sound Card
Contains the circuitry for recording and
reproducing multimedia sound.
ROM BIOS
Stands for Read Only Memory Basic Input
Output System. A collection of software codes built into a PC that handle some
of the fundamental tasks of sending data from one part of the computer to
another.
Serial Ports
Most PCs have two serial ports. They are used
for devices that do not require high data transfer such as a mouse. Those that
require high data transfer, such a printers, are usually connected to the
parallel port.
SIMMS
See circuit boards above.
System Files
Small disk files that contain software code
that are the first files a computer reads from disk when it is booted.
Transistor
Electrical device that has two states - open
or closed. It is therefore ideally suited for the binary system and many
millions are used in the PC to store data.
USB Ports
Stands for Universal Serial Bus. They are a
solution to the PC's lack of interrupts and other system resources to let
software connect directly to peripherals. USBs can connect keyboards, mice,
monitors, printers, and other devices without encountering resource conflicts.
Video Card
Translates image information into the varying
electrical currents needed to display an image on the monitor.
Software, in coordination with the
operating system, sends a burst of electricity along an address line which is a
microscopic strand of electrically conductive material etched into a RAM chip.
This burst identifies where to record data along the many address lines in the
chip. At each memory location in the chip where data can be stored, the pulse
turns on or closes a transistor that is connected to a data line. While the
transistors are turned on, the software sends bursts of electricity along
selected data lines.
When the electrical pulse reaches an
address along which a transistor has been turned on, the pulse flows through the
closed transistor and charges a capacitor. The process repeats itself
continuously to refresh the capacitor's charge, which would otherwise slowly
leak out. When the computer is turned off, the capacitors lose their charges.
Each charged capacitor along the address line represents a 1 bit. An uncharged
capacitor represents a 0 bit.