Notesale: Turn your study into money

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Computer
A computer is a device that accepts information (in the form of digitalized data) and
manipulates it for some result based on a program or sequence of instructions on how the
data is to be processed
...
A
program may be invariable and built into the computer (and called logic circuitry as it is
on microprocessors) or different programs may be provided to the computer (loaded into
its storage and then started by an administrator or user)
...


History of Computer
Most histories of the modern computer begin with the Analytical Engine envisioned by
Charles Babbage following the mathematical ideas of George Boole, the mathematician
who first stated the principles of logic inherent in today's digital computer
...
Apart from
mechanical calculators, the first really useable computers began with the vacuum tube,
accelerated with the invention of the transistor, which then became embedded in large
numbers in integrated circuits, ultimately making possible the relatively low-cost
personal computer
...
Essentially, the program is read by the computer one instruction
at a time, an operation is performed, and the computer then reads in the next instruction,
and so on
...

With the advent of the Internet and higher bandwidth data transmission, programs and

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data that are part of the same overall project can be distributed over a network and
embody the Sun Microsystems slogan: "The network is the computer
...
The English mathematician
and inventor Charles Babbage can be considered its grandfather
...

Babbage worked as a mathematician in Cambridge University where he received his
MA in 1817 and later, like Newton, whose mathematical principles he espoused,
occupied the Lucasian chair in mathematics
...
His statistical
publications include "Table of the Relative Frequency of the Causes of Breaking of Plate
Glass Windows" and "Table of Constants of the Class Mammalia," the minutiae of which
included the heart rate of the pig
...

A prolific disseminator of ideas and an eclectic inventor, Babbage's varied range of
inventions reflected the diversity of his interests
...
He also recorded inventions related to
lighthouse signalling, code breaking, and the postal system
...

Although remembered today primarily for his calculating engines, Babbage left a legacy
in the fields of political theory (he was an ardent industrialist) and operations research
(where his 1832 publication, "On the Economy of Manufactures," cataloged the
manufacturing processes of the day)
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George Boole
George Boole (1815-1864) was a British mathematician and is known as the founder of
mathematical logic
...
In his book,
Boole successfully demonstrated that logic, as Aristotle taught it, could be represented by
algebraic equations
...

In 1855 Boole, the first professor of mathematics at The College of Cork, Ireland,
married Mary Everest, who is now known as a mathematician and teacher in her own
right
...
Unfortunately, Mary's poor
choice of medical treatment may have hastened Boole's death
...
(It seemed logical to her
...

Boole's work in symbolic logic, collectively known as "Boolean algebra", is widely
regarded to be based on the work of earlier mathematician G
...
Leibniz
...
Shannon
demonstrated that Boole's symbolic logic, as it applies to the representation of TRUE and
FALSE, could be used to represent the functions of switches in electronic circuits
...

Today, when using a search engine on the Internet, we use Boole's mathematical concepts
to help us locate information by defining a relationship between the terms we enter
...
Searching for George OR Boole would find
every article in which either the word George or the word Boole appears
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Claude Shannon
Claude Elwood Shannon, a mathematician born in Gaylord, Michigan (U
...
) in 1916, is
credited with two important contributions to information technology: the application of
Boolean theory to electronic switching, thus laying the groundwork for the digital
computer, and developing the new field called information theory
...
Shannon
spent the bulk of his career, a span of over 30 years from 1941 to 1972, at Bell Labs
where he worked as a mathematician dedicated to research
...
Shannon
had the insight to apply the two-valued Boolean logic to electrical circuits (which could
be in either of two states - on or off)
...

Not content with laying the logical foundations of both the modern telephone switch and
the digital computer, Shannon went on to invent the discipline of information theory and
revolutionize the field of communications
...
This concept
says that the more uncertainty in a communication channel, the more information that can

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be transmitted and vice versa
...
He envisioned the
possibility of error-free communications for telecommunications, the Internet, and
satellite systems
...
Information Theory
also has important ramifications for the field of cryptography as explained in his 1949
paper Communication Theory of Secrecy Systems - in a nutshell, the more entropy a
cryptographic system has, the harder the resulting encryption is to break
...
Claude
Shannon died on February 24, 2001
...
In Boolean searching, an
"and" operator between two words or other values (for example, "pear AND apple")
means one is searching for documents containing both of the words or values, not just
one of them
...

In computer operation with binary values, Boolean logic can be used to describe
electromagnetically charged memory locations or circuit states that are either charged (1
or true) or not charged (0 or false)
...
The following table
shows the results from applying AND and OR operations to two compared states:
0 AND 0 = 0 1 AND 0 = 0 1 AND 1 = 1
0 OR 0 = 0 0 OR 1 = 1 1 OR 1 = 1

Vannevar Bush
An electrical engineer by training, Vannevar Bush is credited with having the idea of
hypertext or "instant cross-referencing," decades before the term itself was conceived
by Ted Nelson and before the concept was widely implemented on the World Wide Web
...

Humans, Bush argued, have associative memories where information is accessed by
following a series of mental links and pathways
...


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The bulk of Bush's career was spent at MIT's Department of Electrical Engineering where
he became Dean
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The Differential Analyser was
notable for its use of decimal rather than the binary number system
...
He was the driving force behind the founding of the National Science Foundation
...
Bush's primary
legacy remains that of the hypertext concept - he is remembered as a forefather of the
World Wide Web
...

A broader definition comes from the organization that Web inventor Tim Berners-Lee
helped found, the World Wide Web Consortium (W3C):
"The World Wide Web is the universe of network-accessible information, an
embodiment of human knowledge
...
Relative to today's computers and transmission media,
data is information converted into binary digital form
...

3) In telecommunications, data sometimes means digital-encoded information to
distinguish it from analog-encoded information such as conventional telephone voice
calls
...
Data transmission can often be sent
with intermittent connections in packets that arrive in piecemeal fashion
...

Some authorities and publishers, cognizant of the word's Latin origin and as the plural
form of "datum," use plural verb forms with "data"
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INFORMATION
Information is stimuli that has meaning in some context for its receiver
...


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After processing (such as formatting and printing), output data can again be perceived as
information
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Binary Digits
Binary describes a numbering scheme in which there are only two possible values for
each digit: 0 and 1
...
In digital data memory, storage, processing,
and communications, the 0 and 1 values are sometimes called "low" and "high,"
respectively
...

In the modern computer that John von Neumann outlined in 1945, the program contains a
one-at-a-time sequence of instructions that the computer follows
...
The computer gets one instruction
and performs it and then gets the next instruction
...
(Note that a program is also a special
kind of "data" that tells how to operate on "application or user data
...
Your
language statements are the source program
...
There are several
synonyms for object program, including object module and compiled program
...

The machine language of the computer is constructed by the language compiler with an
understanding of the computer's logic architecture, including the set of possible computer
instructions and the length (number of bits) in an instruction
...
Designed in the 1830s by the English mathematician and inventor Charles
Babbage, the Analytical Engine introduced a number of computing concepts still in use
today
...

Input and output was provided using punched cards, based on the invention by Jacquard
in the early 1800s
...
He envisaged the computer to
be constructed with brass fittings and powered by steam
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Difference Engine
The Difference Engine, designed in the 1820s by the English mathematician and inventor
Charles Babbage, was intended to automatically compute mathematical tables which,
until that time, had been tediously calculated by hand and were prone to error
...

With good political contacts and the ear of Prime Ministers, Babbage was able to acquire
initial funding for the construction of his machine, a task expected to last 3 years
...
In 1827, family tragedies,
including the death of his wife, led Babbage to escape in travels to the Continent
...
In the meantime,
Babbage had designed a general-purpose computer, the Analytical Engine
...

By this stage, the 1840's, times were hard and a government which had already spent as
much as 17,000 English pounds with little reward declined to continue financing his
plans
...
The Difference Engine was eventually built in 1991, the
bicentennial of Babbage's birth, using the technology of the era as proof that Babbage's
designs were valid
...

Babbage was assisted in his endeavours by Ada Augusta, Countess of Lovelace (and
daughter of the poet Byron) who is regarded as the world's first computer programmer for
her work with Babbage
...

While Babbage's earlier Difference Engine was finally contructed in 1991, his Analytical
Engine remains unrealized
...


The Five Generations of Computers
The history of computer development is often referred to in reference to the different
generations of computing devices
...

Read about each generation and the developments that led to the current devices that we
use today
...
They were very expensive to operate
and in addition to using a great deal of electricity, generated a lot of heat, which was
often the cause of malfunctions
...
Input was based on punched cards and paper tape, and output was
displayed on printouts
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The UNIVAC was the first commercial computer delivered to a business client,
the U
...
Census Bureau in 1951
...

The transistor was invented in 1947 but did not see widespread use in computers until the
late 1950s
...
Though the transistor still generated a great deal of heat that
subjected the computer to damage, it was a vast improvement over the vacuum tube
...

Second-generation computers moved from cryptic binary machine language to symbolic,
or assembly, languages, which allowed programmers to specify instructions in words
...
These were also the first computers that stored their
instructions in their memory, which moved from a magnetic drum to magnetic core
technology
...

Third Generation (1964-1971) Integrated Circuits
The development of the integrated circuit was the hallmark of the third generation of
computers
...

Instead of punched cards and printouts, users interacted with third generation computers
through keyboards and monitors and interfaced with an operating system, which allowed
the device to run many different applications at one time with a central program that
monitored the memory
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Fourth Generation (1971-Present) Microprocessors
The microprocessor brought the fourth generation of computers, as thousands of
integrated circuits were built onto a single silicon chip
...
The Intel 4004 chip, developed in

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1971, located all the components of the computer—from the central processing unit and
memory to input/output controls—on a single chip
...
Microprocessors also moved out of the realm of desktop
computers and into many areas of life as more and more everyday products began to use
microprocessors
...
Fourth generation
computers also saw the development of GUIs, the mouse and handheld devices
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The use of parallel processing and superconductors is helping to make
artificial intelligence a reality
...
The goal of fifth-generation
computing is to develop devices that respond to natural language input and are capable of
learning and self-organization
...

They can also be classified in different ways
...

A computer that is used in a home differs in size and shape from the computer being used
in a hospital
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A student carrying a laptop with him to his college is different in shape and size from all
the computers mentioned above
...
We will
discuss what are in classifications and what job they perform
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It can process trillions of instructions in seconds
...

Governments specially use this type of computer for their different calculations and
heavy jobs
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In most of the Hollywood’s movies it is used for animation purposes
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Mainframes
Another giant in computers after the super computer is Mainframe, which can also
process millions of instruction per second and capable of accessing billions of data
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This is normally to expensive and out of reach from a salary-based person who wants a
computer for his home
...

Minicomputer
This computer is next in he line but less offers less than mainframe in work and
performance
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Personal computers
Almost all the computer users are familiar with the personal computers
...

This is the computer mostly preferred by the home users
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This computer is small in size and you can easily arrange it to fit in your single bedroom
with its all accommodation
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What is an operating system?
An operating system (sometimes abbreviated as "OS") is the program that, after being
initially loaded into the computer by a boot program, manages all the other programs in a
computer
...
The
application programs make use of the operating system by making requests for services
through a defined application program interface (API)
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Computer instructions or data
...
The storage devices and display
devices are hardware
...
For example,
you can say: "The problem lies in the software," meaning that there is a problem with the
program or data, not with the computer itself
...
"
The distinction between software and hardware is sometimes confusing because they are
so integrally linked
...
But
to buy the software, you need to buy the disk (hardware) on which the software is
recorded
...
It Include the operating system and all
the utilities that enable the computer to function
...
For example,
word processors, spreadsheets, and database management systems fall under the
category of applications software
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

Languaged Processor: This is the part of the software through which one can
develop the above and other type software
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It consists of a television picture tube that had been modified to accept the
type of video signal created by the computer's electronics
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The picture
quality leaves something to be desired
...
These are technically not the
same thing as pixels, but the terms are often used
interchangeably
...
Therefore 1024 x 768 resolution
will be sharper than 800 x 600 resolution because the
former uses more lines creating a denser, more detailed
picture
...
For text, resolution isn't as critical
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Because
each transistor is so small, the amount of charge
needed to control it is also small
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Prior to TFT, passive matrix LCD displays
could not keep up with fast moving images
...
A TFT monitor can
track the mouse, resulting in a display that can be used for video, gaming and all forms of
multimedia
...
Most buy their TFTs because they look better than CRT monitors and because
the price differentials are much lower than what they used to be
...
Some times we get through and some times
we don't
...

Traditionally all computer monitors used to be CRT monitors which are quite similar to
the CRT televisions we have in our homes
...
However as technology advanced and the price
differences between CRTs and TFTs came down it became viable to sell computers with
TFT (or LCD) monitors
...

The major differences between the two are
1) CRT monitors are bulky and consume a lot of table space where as TFT monitors are
thin and occupy less space
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3) CRT monitors have much much faster response times than TFT monitors
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4) TFT monitors consume less power than CRT monitors
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5) TFT monitors looks more elegant than CRT monitors
...
In other
words CRT monitors display colors much better than TFT monitors
...

1) You save 70W when you use a 15" TFT monitor instead of a 15" CRT monitor
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So depending on
your usage patter you can see how long it would take to break even on the cost
differential through energy savings
...
The equation used is
simple; No of days for breaking even = ((Cost Differential/Cost per unit)*14)/(Hours

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used per day)
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2) If you are a graphics artist and you require close to realistic representation of colors
you will have to go for a CRT monitor irrespective of any other factors
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If you play very fast moving games then
response times of the monitors comes into play and you might end up having to buy a
CRT monitor to get a smooth gaming experience
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4) If you have to move your residence frequently as part of your job and you have to have
a desktop, then a TFT monitor would make more sense
...

5) If you are running a software development center it might be wiser to select TFTs for
your software developers and CRTs for your graphics guys
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6) If you are running a retail outlet a TFT would give your POS counter a more
professional look and also help you save on your electricity bills
...

If you need help in deciding between a TFT monitor or a CRT monitor, do get in touch
with us using the comments form below and we will try to help you in making your
decision
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A
computer keyboard closely resembles a conventional typewriter keyboard with the
addition of numerous keys that are used specifically for computing functions

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The Mouse
Named for the resemblance of the wire coming out of it and a mouse's tail, the mouse
was introduced to computing in the early 1980's when Macintosh created its graphical
user interface (GUI)
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Using the mouse and keyboard in combination allows
the computer user substantial latitude in how to accomplish a wide variety of tasks
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The CPU is the brain, and the motherboard is the nervous
system
...
Fast
communication isn't as important as reliable communication though
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The motherboard is the circuit board to which all the other components of the computer
connect in some way
...
all plug into the
motherboard's various slots and connectors
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Printers
A device that prints text or illustrations on paper
...
In terms of the technology utilized, printers fall into the following categories:
daisy-wheel: Similar to a ball-head typewriter, this type of printer has a plastic or metal
wheel on which the shape of each character stands out in relief
...
Daisy-wheel printers produce letter-quality print but cannot print graphics
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Each pin makes a
dot, and combinations of dots form characters and illustrations
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Ink-jet printers produce high-quality text and
graphics
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Laser printers produce very high
quality text and graphics
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line printer: Contains a chain of characters or pins that print an entire line at one time
...

thermal printer: An inexpensive printer that works by pushing heated pins against heatsensitive paper
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Printers are also classified by the following characteristics:
Quality of type: The output produced by printers is said to be either letter quality (as good
as a typewriter), near letter quality, or draft quality
...
Some dot-matrix printers claim letter-quality print,
but if you look closely, you can see the difference
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Daisy-wheel printers tend to be the slowest, printing about 30 cps
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Dot-matrix printers can print up to
500 cps, and laser printers range from about 4 to 20 text pages per minute
...
Daisy-wheel, dot-matrix, and line printers are impact printers
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The important difference between
impact and non-impact printers is that impact printers are much noisier
...
Other printers
can print both text and graphics
...
In
contrast, laser and ink-jet printers are capable of printing an almost unlimited variety of
fonts
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STORAGE
In a computer, storage is the place where data is held in an electromagnetic or optical
form for access by a computer processor
...


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1) Storage is frequently used to mean the devices and data connected to the computer
through input/output operations - that is, hard disk and tape systems and other forms of
storage that don't include computer memory and other in-computer storage
...
This meaning is probably more common in the IT industry
than meaning 2
...

Primary storage is much faster to access than secondary storage because of the
proximity of the storage to the processor or because of the nature of the storage devices
...


Primary Storage
MEMORY
is the electronic holding place for instructions and data that your computer's
microprocessor can reach quickly
...
Memory is often used as a
shorter synonym for random access memory (RAM)
...

The more RAM you have, the less frequently the computer has to access instructions and
data from the more slowly accessed hard disk form of storage
...
Storage devices include hard disks, floppy disks, CD-ROM, and tape backup
systems
...

Additional kinds of integrated and quickly accessible memory are read-only memory
(ROM), programmable ROM (PROM), and erasable programmable ROM (EPROM)
...
On today's
smaller computers, especially personal computers and workstations, the term random
access memory (RAM)
...

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The terms main storage and auxiliary storage originated in the days of the mainframe
computer to distinguish the more immediately accessible data storage from storage that
required input/output operations
...

2) Primary storage is sometimes used to mean storage for data that is in active use in
contrast to storage that is used for backup purposes
...
(It should be noted that, although
these two meanings conflict, the appropriate meaning is usually apparent from the
context
...


Random Access Memory
RAM (random access memory) is the place in a computer where the operating system,
application programs, and data in current use are kept so that they can be quickly reached
by the computer's processor
...
However, the
data in RAM stays there only as long as your computer is running
...
When you turn your computer on again, your operating
system and other files are once again loaded into RAM, usually from your hard disk
...
The short-term memory focuses on work at hand, but can only keep so
many facts in view at one time
...
A computer also works this
way
...
Unlike the hard disk
which can become completely full of data so that it won't accept any more, RAM never
runs out of memory
...

How Big is RAM?
RAM is small, both in physical size (it's stored in microchips) and in the amount of data
it can hold
...
A typical computer may come with 256
million bytes of RAM and a hard disk that can hold 40 billion bytes
...
These holes connect through a bus or set
of electrical paths to the processor
...

Most personal computers are designed to allow you to add additional RAM modules up
to a certain limit
...
(RAM access time is in nanoseconds; hard
disk access time is in milliseconds
...

Originally, the term distinguished regular core memory from offline memory, usually on
magnetic tape in which an item of data could only be accessed by starting from the
beginning of the tape and finding an address sequentially
...
RAM is
organized and controlled in a way that enables data to be stored and retrieved directly to
specific locations
...

In addition to disk, floppy disk, and CD-ROM storage, another important form of storage
is read-only memory (ROM), a more expensive kind of memory that retains data even
when the computer is turned off
...

READ ONLY MEMORY
ROM is "built-in" computer memory containing data that normally can only be read, not
written to
...
Unlike a computer's random access memory
(RAM), the data in ROM is not lost when the computer power is turned off
...

If you ever do the hardware setup procedure with your computer, you effectively will be
writing to ROM
...

Semiconductor based
Classic mask-programmed ROM chips are integrated circuits that physically encode the
data to be stored, and thus it is impossible to change their contents after fabrication
...
Typically, this device uses high voltages to permanently destroy or
create internal links (fuses or antifuses) within the chip
...

 Erasable programmable read-only memory (EPROM) can be erased by
exposure to strong ultraviolet light (typically for 10 minutes or longer), then
rewritten with a process that again requires application of higher than usual

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voltage
...
EPROM chip packages can often be identified by the prominent
quartz "window" which allows UV light to enter
...
Some EPROM
chips are factory-erased before they are packaged, and include no window; these
are effectively PROM
...
Writing or
flashing an EEPROM is much slower (milliseconds per bit) than reading from a
ROM or writing to a RAM (nanoseconds in both cases)
...
Writing is a very slow
process and again requires higher voltage (usually around 12 V) than is
used for read access
...
EAROM may be used as nonvolatile storage for critical system setup information; in many
applications, EAROM has been supplanted by CMOS RAM supplied by
mains power and backed-up with a lithium battery
...
Flash memory can be erased and rewritten faster than ordinary
EEPROM, and newer designs feature very high endurance (exceeding
1,000,000 cycles)
...
Flash memory is sometimes called flash ROM or flash
EEPROM when used as a replacement for older ROM types, but not in
applications that take advantage of its ability to be modified quickly and
frequently
...


SECONDARY STORAGE
Secondary storage, sometimes called auxiliary storage, is all data storage that is not
currently in a computer's primary storage or memory
...

In a personal computer, secondary storage typically consists of storage on the hard disk
and on any removable media, if present, such as a CD or DVD
...
Today's computers typically come
with a hard disk that contains several billion bytes (gigabytes) of storage
...
A "head"
(something like a phonograph arm but in a relatively fixed position) records (writes) or
reads the information on the tracks
...
Each read or write operation requires that data be located,
which is an operation called a "seek
...
)
A hard disk/drive unit comes with a set rotation speed varying from 4500 to 7200 rpm
...
Although the physical location can be
identified with cylinder, track, and sector locations, these are actually mapped to a logical
block address (LBA) that works with the larger address range on today's hard disks
...
The term usually refers to the magnetic medium housed in a rigid
plastic cartridge measuring 3
...
Also called a
"3
...
44 megabytes (MB) of data
...
5-inch diskette drive pre-installed, some
notebook computers and centrally-administered desktop computers omit them
...
25 inches square,
about 1 millimeter thick, and capable of holding 1
...
These were
sometimes called "floppy disks" or "floppies" because their housings are flexible
...
25-inch diskettes have been largely replaced by 3
...
Many people also call the newer hard-cased diskette a
"floppy
...

However, the magneto-optical (MO) disk is more popular for mass storage, backup, and
archiving
...
5-inch
magnetic diskette
...

COMPACT DISC
A compact disc [sometimes spelled disk] (CD) is a small, portable, round medium made
of molded polymer (close in size to the floppy disk) for electronically recording, storing,
and playing back audio, video, text, and other information in digital form
...
At home,
CDs have tended to replace the tape cartridge although the latter is still widely used in
cars and portable playback devices
...
CDs
will probably continue to be popular for music recording and playback
...

Some variations of the CD include:
 CD-ROM
o CD-ROM (Compact Disc, read-only-memory) is an adaptation of the CD
that is designed to store computer data in the form of text and graphics, as
well as hi-fi stereo sound
...
Other standards are used in
conjunction with it to define directory and file structures, including ISO
9660, HFS (Hierarchal File System, for Macintosh computers), and
Hybrid HFS-ISO
...
75 inches) in diameter and 1
...
05
inches) thick and is composed of a polycarbonate plastic substrate
(underlayer - this is the main body of the disc), one or more thin reflective
metal (usually aluminum) layers, and a lacquer coating
...
CD-i was specified as an entire system,
comprising not just a disc and data format, but a hardware and software
system, a variety of special compression methods for audio and visual
data, and a method of interleaving audio, video, and text data
...
Full screen motion video capabilities were
added to the original specification later
...
The CD-RW format was
introduced by Hewlett-Packard, Mitsubishi, Philips, Ricoh, and Sony, in a
1997 supplement to Philips and Sony's Orange Book
...
Prior to the release of the
Orange Book, CDs had been read-only audio (CD-Digital Audio,
described fully in the Red Book), to be played in CD players, and
multimedia (CD-ROM), to be played in computers' CD-ROM drives
...
CD-RW drives can write
both CD-R and CD-RW discs and can read any type of CD
...
CD-ROM XA was developed jointly by Sony, Philips, and
Microsoft, and its specifications were published in an extension to the
Yellow Book
...
The images can also be
printed out on photographic paper with a special Kodak machine
Video CD
o VCD (also called video CD, video compact disc or "disc") is a compact
disk format based on CD-ROM XA that is specifically designed to hold
MPEG-1 video data and to include interactive capabilities
...
Each VCD disk holds 72-74 minutes of video and has a data
transfer rate of 1
...
VCDs can be played on a VCD player
connected to a television set (in the same way that video cassettes can on a
VCR) or computer, on a CD-i player, on some CD-ROM drives, and some
DVD players
...
7 gigabyte storage capacity on a single-sided,
one-layered disk, which is enough for a 133-minute movie
...
This compares to 650
megabytes (
...

Formats:
 DVD-Video is the format designed for full-length movies that work with your
television set
...
The DVD drive
will usually also play regular CD-ROM discs and DVD-Video disks
...

 DVD-Audio is a CD-replacement format
...

DVD was originally said to stand for digital video disc, and later for digital versatile disc
...

Virtual Memory Definition
Virtual memory is the use of space on a hard disk drive (HDD) to simulate additional
main memory
...
Physically, main memory (also referred to as
primary memory) consists of random access memory (RAM) chips that are combined into
modules which, in turn, are inserted into slots on the motherboard (i
...
, the main circuit
board) on a computer
...
e
...


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In order to free up space in memory, an operating system with a virtual memory
capability transfers data that is not immediately needed from memory to the HDD; when
that data is needed again, it is copied back into memory
...
g
...

Virtual memory permits software to run in a memory space (i
...
, a logical memory)
whose size is greater than the computer's RAM
...
While this is huge in comparison to what was
common just a few years ago, it is still often insufficient to simultaneously run all of the
programs that users attempt to run
...

Application programs cannot distinguish between primary memory and virtual memory,
and thus they run as if all the data is in primary memory
...
However, its existence can become apparent in the form of
degraded performance if it is used too heavily, because the CPU (central processing unit)
will spend more of its time copying data back and forth to the HDD and less of its time
doing useful work
...
The reduced efficiency is also a result of the
facts that HDDs are far slower than RAM and that they are not designed for accessing
small pieces of data (e
...
, single bytes) one at a time
...
This is because it provides a large benefit to users at a very low
cost
...

The space on a HDD that is used to store the overflow from memory is called swap
space
...
e
...
It is generally recommended that the size of the swap partition be about
twice the amount of system RAM
...
When an address is referenced, the page is swapped into
memory
...
This
management of virtual memory is performed by a type of hardware circuitry called a
memory management unit (MMU)
...
In order to facilitate this switching, CPUs also

24

maintain a table of recently used main-to-virtual memory translations, called a translation
lookaside buffer (TLB)
...
It was apparently first employed at the
University of Manchester in the UK for the Atlas Computer, which was completed in
1962
...
Virtual memory was incorporated into the UNIX kernel (i
...
, the
core of the operating system) in the 1970s as part of the Berkeley Extensions, which were
developed at the University of California at Berkeley (UCB)
...
e
...
e
...
e
...


MICRO CHIP
A microchip (sometimes just called a "chip") is a unit of packaged computer circuitry
(usually called an integrated circuit) that is manufactured from a material such as silicon
at a very small scale
...
Microchips are also made that
include both logic and memory and for special purposes such as analog-to-digital
conversion, bit slicing, and gateways
...
An IC can function as an amplifier, oscillator, timer, counter, computer
memory, or microprocessor
...


MICROPROCESSOR
A microprocessor is a computer processor on a microchip
...
It is the "engine" that goes into motion when you turn your computer on
...
Typical microprocessor operations include
adding, subtracting, comparing two numbers, and fetching numbers from one area to
another
...
When the computer is turned on, the microprocessor is designed
to get the first instruction from the basic input/output system (BIOS) that comes with the
computer as part of its memory
...


25

PROCESSOR
A processor is the logic circuitry that responds to and processes the basic instructions
that drive a computer
...
The
processor in a personal computer or embedded in small devices is often called a
microprocessor
...
It also manages data flow between the computer's
operating system and attached devices such as the hard disk, video adapter, keyboard,
mouse, and printer
...
(In
contrast, the operating system can either be preinstalled by the manufacturer or vendor or
installed by the user)
...
When you turn on your
computer, the microprocessor passes control to the BIOS program, which is always
located at the same place on EPROM
...

With BIOS, your operating system and its applications are freed from having to
understand exact details (such as hardware addresses) about the attached input/output
devices
...

Sometimes this change can be made during your system setup
...

Although BIOS is theoretically always the intermediary between the microprocessor and
I/O device control information and data flow, in some cases, BIOS can arrange for data to
flow directly to memory from devices (such as video cards) that require faster data flow
to be effective
...
At the
lowest level, each instruction is a sequence of 0s and 1s that describes a physical
operation the computer is to perform (such as "Add") and, depending on the particular
instruction type, the specification of special storage areas called registers that may
contain data to be used in carrying out the instruction, or the location in computer
memory of data
...
In high-level languages, a language statement generally
results (after program compilation) in multiple processor instructions
...


REGISTER
In a computer, a register is one of a small set of data holding places that are part of a
computer processor
...
Some instructions specify
registers as part of the instruction
...
A register must be large enough to hold an instruction - for example, in a 32-bit
instruction computer, a register must be 32 bits in length
...

Depending on the processor design and language rules, registers may be numbered or
have arbitrary names
...

Some people call these instructions assembler language and others use the term assembly
language
...
A bit has a single
binary value, either 0 or 1
...
In most computer systems, there are eight bits in a byte
...

four bits is called a nibble
...
In many systems, four eight-bit bytes or octets form a 32-bit word
...

In most computer systems, a byte is a unit of data that is eight binary digits long
...

A byte can also hold a string of bits that need to be used in some larger unit for
application purposes (for example, the stream of bits that constitute a visual image for a
program that displays images or the string of bits that constitutes the machine code of a

27

computer program)
...
(A bit is abbreviated with a small
"b"
...
For example, an 820 MB
hard drive holds a nominal 820 million bytes - or megabytes - of data
...
For
example, one megabyte ("one million bytes") is actually 1,048,576 (decimal) bytes
...


Introduction to the concept of a bus
A bus, in computing, is a set of physical connections (cables, printed circuits, etc
...

The purpose of buses is to reduce the number of "pathways" needed for communication
between the components, by carrying out all communications over a single data channel
...


If only two hardware components communicate over the line, it is called a hardware
port (such as a serial port or parallel port)
...
It is a
unidirectional bus
...
It is a
bidirectional bus
...
It is a
bidirectional bus, as it also transmits response signals from the hardware
...
The internal
bus allows the processor to communicate with the system's central memory (the
RAM)
...
) to communicate with one another
...




29



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