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Chapter 5
Chapter 5
The System Unit
5.1 Microchips, Miniaturization, & Mobility
From Vacuum Tubes to Transistors to Microchips
The ENIAC was the last computer to use vacuum tubes, in 1946. The ENIAC
employed 18,000 vacuum tubes; unfortunately, a tube failure occurred every 7
minutes and it took more than 15 minutes to find and replace the faulty tube.
A transistor is essentially a tiny electrically operated switch that can alternate
between “on” and “off” many millions of times per second. The first transistors
were one-hundredth the size of a vacuum tube, needed no warm-up time,
consumed less energy, and were faster and more reliable. Transistors marked
the beginning of a process of miniaturization that has not ended yet. Today
more than 3 million transistors can be squeezed into a half centimeter.
Today, transistors are part of an integrated circuit—an entire electronic
circuit, including wires, formed on a single “chip,” or piece, of special material,
usually silicon. An integrated circuit embodies what is called solid-state
technology. Solid state means that the electrons are traveling through solid
material—in this case, silicon.
Silicon is an element that is widely found in clay and sand. It is used not only
because its abundance makes it cheap but also because it is a
semiconductor. A semiconductor is material whose electrical properties are
intermediate between a good conductor of electricity and a nonconductor of
electricity.
A chip, or microchip, is a tiny piece of silicon that contains millions of
microminiature electronic circuit components, mainly transistors.
Miniaturization Miracles: Microchips, Microprocessors, & Micromachines
Microchips—“industrial rice,” as the Japanese call them—are responsible for
the miniaturization that has revolutionized consumer electronics, computers,
and communications. They store and process data in all the electronic
gadgetry we’ve become accustomed to.
There are different kinds of microchips: microprocessor, memory, logic,
communications, graphics and math coprocessor chips. Perhaps the most
important is the microprocessor chip. A microprocessor (“microscopic
processor” or “processor on a chip”) is the miniaturized circuitry of a computer
processor—the part that processes, or manipulates, data into information.
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When modified for use in machines other than computers, microprocessors
are called microcontrollers, or embedded computers.
Mobility
In the 1980s portability, or mobility, meant trading off computing power and
convenience in return for smaller size and weight. Today, however, we are
getting close to the point where we do not have to give up anything. Experts
have predicted that small, powerful, wireless personal electronic devices will
transform our lives far more than the personal computer has done so far.
5.2 The System Unit
The Binary System: Using Two States
Binary system has only two digits: 0 and 1. In the computer, the 0 can be
represented by the electrical current being off and the 1 by the current being
on. All data and programs that are used by a computer are represented in
terms of these binary numbers.
Capacity is denoted by any of the following:

Bit: In the binary system, each 0 or 1 is called a bit, which is short for
“binary digit.”

Byte: A group of eight bits is called a byte, and a byte represents one
character, digit, or other value.

Kilobyte: A kilobyte (K, KB) is about 1000 bytes. (Actually, it’s precisely
1024 bytes, but the figure is commonly rounded.) The kilobyte was a
common unit of measure for memory or secondary-storage capacity in
older computers.

Megabyte: A megabyte (M, MB) is about 1 million bytes (1,048,576
bytes). Most measures of microcomputer primary storage capacity today
are expressed in megabytes.

Gigabyte: A gigabyte (G, GB) is about 1 billion bytes (1,073,741,824
bytes). This measure was formerly used with “big iron” types of computers,
but now is typical of secondary storage (hard disk) capacity of today’s
microcomputers.

Terabyte: A terabyte (T, TB) represents about 1 trillion bytes
(1,009,511,627,776 bytes).

Petabyte: A petabyte (P, PB) represents about 1 quadrillion bytes
(1,048,576 gigabytes).
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
ASCII: Pronounced “askey,” ASCII stands for American Standard Code for
Information Interchange and is the binary code most widely used with
microcomputers.

EBCDIC: Extended Binary Coded Decimal Interchange Code—is used
with large computers, such as mainframes.

Unicode uses two bytes (16 bits) for each character, rather than one byte
(8 bits). Instead of the 256 character combinations of ASCII-8, Unicode
can handle 65,536 character combinations, thus allowing almost all the
written languages of the world to be represented using a single character
set.
The Parity Bit
Dust, electrical disturbance, weather conditions, and other factors can cause
interference in a circuit or communications line that is transmitting a byte. A
data error can be detected by using a parity bit. A parity bit, also called a
check bit, is an extra bit attached to the end of a byte for purposes of checking
for accuracy. Parity schemes may be even parity or odd parity.
Machine Language
Machine language is a binary-type programming language that the computer
can run directly. To most people, an instruction written in machine language,
consisting only of 0s and 1s, is incomprehensible. To the computer, however,
the 0s and 1s represent precise storage locations and operations.
The Computer Case: Bays, Buttons, & Boards
The system unit houses the motherboard (including the processor chip and
memory chips), the power supply, and storage devices. In computer ads, the
part of the system unit that is the empty box with just the power supply is
called the case or system cabinet.
A bay is a shelf or opening used for the installation of electronic equipment,
generally storage devices such as a hard drive or DVD drive. A computer may
come equipped with four or seven bays. A tower is a cabinet that is tall,
narrow, and deep.
Power Supply
The power supply is a device that converts AC current (electricity available
from a standard wall outlet) to DC current to run the computer. Because
electricity can generate a lot of heat, a fan inside the computer keeps the
power supply and other components from becoming too hot.
The three principal types of power protection devices are:
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
Surge protector: is a device that protects a computer from being
damaged by momentary surges (spikes) of high voltage.

Voltage regulator: is a device that protects a computer from being
damaged by insufficient power—“brownouts” or “sags” in voltage.

UPS: (uninterruptable power supply) is a battery-operated device that
acts as a surge protector and provides a computer with electricity if there is
a power failure.
5.3 The Motherboard & Microprocessor Chip
The motherboard, or system board, is the main circuit board in
unit. The motherboard consists of a flat board that fills one side of
contains both soldered, nonremovable components and sockets
components that can be removed—microprocessor chip, RAM
various expansion cards.
the system
the case. It
or slots for
chips, and
Expansion is a way of increasing a computer’s capabilities by adding
hardware to perform tasks that are beyond the scope of the basic system. For
example, you might want to add video and sound cards. Upgrading means
changing to newer, usually more powerful or sophisticated versions, such as
more powerful microprocessors or more memory chips.
CISC (complex instruction set computing) chips, which are used mostly in
PCs and in conventional mainframes, can support a large number of
instructions, but at relatively low processing speeds.
RISC (reduced instruction set computing) chips, which are used mostly in
workstations, a great many seldom-used instructions are eliminated. As a
result, workstations can work up to 10 times faster then most PCs.
Processing Speeds: From Megahertz to Picoseconds

For microcomputers—megahertz and gigaherz: Micro-computer
microprocessor speeds are usually expressed in megahertz (MHz),
millions of machine cycles per second, which is also the measure of a
microcomputer’s clock speed. A high-end microcomputer or workstation
might perform at 100 MIPS or more, a mainframe at 200–1200 MIPS.
The latest generation of processors operates in gigahertz (GHz)—a billion
cycles per second. Intel’s latest chip, the Pentium 4, operates at 1.4
gigahertz.

For workstations, minicomputers, and mainframes—MIPS: Processing
speed can also be measured according to the number of instructions
processed per second that a computer can process, which today is in the
millions. MIPS is a measure of a computer’s processing speed; MIPS
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stands for millions of instructions per second that the processor can
perform.

For supercomputers—flops: The abbreviation flops stands for floatingpoint operations per second, a floating-point operation being a special kind
of mathematical calculation. This measure is expressed as megaflops
(mflops, or millions of floating-point operations per second), gigaflops
(gflops, or billions), and teraflops (tflops, or trillions).

For all computers—fractions of a second: Another way to measure
cycle times is in fractions of a second. A microcomputer operates in
microseconds, a supercomputer in nanoseconds or picoseconds—
thousands or millions of times faster.
How the Processor or CPU Works: Control Unit, ALU, & Registers
Word size: the number of bits that the processor may process at any one
time.
CPU (central processing unit) is the “brain” of the computer; it follows the
instructions of the software (program) to manipulate data into information.
5.4 How Memory Works: RAM, ROM, CMOS, & Flash
RAM chips—to temporarily store program instructions and data: Primary
storage is temporary or working storage and is often called memory or main
memory; secondary storage is relatively permanent storage.
RAM (random access memory) chips are for primary storage; they temporarily
hold (1) software instructions and (2) data before and after it is processed by the
CPU. Because its contents are temporary, RAM is said to be volatile—the
contents are lost when the power goes off or is turned off.
ROM chips—to store fixed start-up instructions: Unlike RAM, to which data
is constantly being added and removed, ROM (read-only memory) cannot be
written on or erased by the computer user without special equipment. ROM
chips contain fixed start-up instructors—programs that are built in at the
factory—that are necessary for basic computer operations.
CMOS
chips—to
store
flexible
start-up
instructions:
CMOS
(complementary metal-oxide semiconductor) chips are powered by a battery
and thus don’t lose their contents when the power is turned off.
Flash memory chips—to store flexible programs: Also a nonvolatile form of
memory, flash memory chips can be erased and reprogrammed more than
once, and do not require a battery.
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How Cache Works: Level 1 (Internal) & Level 2 (External)
Cache temporarily stores instructions and data that the processor is likely to use
frequently. Thus, cache speeds up processing.
There are two kinds of cache—Level 1 and Level 2:

Level 1 (L1) cache—part of the microprocessor chip: Level 1 (L1)
cache, also called internal cache, is built into the processor chip. Its capacity is
less than that of Level 2 cache, although it operates faster.

Level 2 (L2) cache—not part of the microprocessor chip: Level 2 (L2)
cache, also called external cache, resides outside the processor chip and
consists of SRAM chips.
Other Methods of Speeding Up Processing: Interleaving, Bursting & Pipelining
Interleaving: a process in which the CPU alternated communication between
two or more memory banks.
Bursting: Provides the CPU with additional data from memory based on the
likelihood that it will be needed.
Pipelining: Divides a task into a series of stages with some of the work
completed at each stage.
5.5 Ports & Cables
Port: A connecting socket or jack on the outside of the system unit into which
are plugged different kinds of cables. A port allows you to plug in a cable or
connect a peripheral device, such as a monitor, printer, or modem, so that it
can communicate with the computer system.
Ports are of several types:

Serial ports: for transmitting slow data over long distances: A line
connected to a serial port will send bits one after another, like cars on a
one-lane highway.

Parallel ports—for transmitting fast data over short distances: A line
connected to a parallel port allows 8 bits (1 byte) to be transmitted
simultaneously.

SCSI ports—for transmitting fast data to up to seven devices in a
daisy chain: A SCSI (small computer system interface) port allows data
to be transmitted in a “daisy chain” to up to 7 devices at speeds (32 bits at
a time) higher than those possible with serial and parallel ports.
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
USB ports—for transmitting data to up to 127 devices in a daisy
chain: A USB (universal serial bus) port can theoretically connect up to
127 peripheral devices daisy-chained to one general-purpose port.

Plug and Play, which allows peripheral devices and expansion cards to be
automatically configured while they are being installed.

Dedicated ports—for keyboard, mouse, phone, and so on: The back of
a computer also has other, dedicated ports—ports for special purposes.
Among these are the round ports for connecting the keyboard and the
mouse. There are also jacks for speakers and microphones and modemto-telephone jacks. Finally, there is one connector that is not a port at all—
the power plug socket, into which you insert the power cord that brings
electricity from a wall plug.

Infrared ports—for cableless connections over a few feet: An infrared
port allows a computer to make a cableless connection with infraredcapable devices.
5.6 Expandability: Buses & Cards
Expansion slots are sockets on the motherboard into which you can plug
expansion cards.
Expansion cards—also known as expansion boards, adapter cards, interface
cards, plug-in boards, controller cards, add-ins, or add-ons—are circuit boards
that provide more memory or that control peripheral devices.
The following are all types of expansion cards:





Graphics cards—for monitors
Sound cards—for speakers and audio output
Modem cards—for remote communication via phone lines
Network interface cards—for remote communication via cable
PC Cards—for laptop computers
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5.7 Future Developments in Processing & Storage
DSP Chips: Processors for the Post-PC Era
Digital signal processors (DSPs) are integrated circuits designed for highspeed data manipulation and used in audio, communications, and image
manipulation. DSPs are designed to manipulate digital signals in speech,
music, and video.
Nanotechnology
A nanometer is a billionth of a meter, which means we are operating at the
level of atoms and molecules.
Optical Computing
Tomorrow’s computer might be optical, or opto-electronic—using light, not
electricity. With optical technology, a machine using lasers, lenses, and mirrors
would represent the on/off codes of data with pulses of light.
DNA Computing
Potentially, biotechnology could be used to grow cultures of bacteria that,
when exposed to light, emit a small electrical charge, for example. The
properties of this “biochip” could be used to represent the on/off digital signals
used in computing.
Quantum Computing
Sometimes called the “ultimate computer,” the quantum computer is based on
quantum mechanics, the theory of physics that explains the erratic world of the
atom. A quantum computer stores information by using states of elementary
particles. Scientists envision using the energized and relaxed states of
individual atoms to represent data.
Other Possibilities: Molecular & Dot Computers
In the molecular computer, the silicon transistor is replaced with a single
molecule. In the dot computer, the transistor is replaced by a single electron.
These two approaches face formidable technical problems, such as massproducing atomic wires and insulators. No viable prototypes yet exist.
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