Notes on Information Technology
(The following notes on various topic can be used for as a question's answer or as a short note)
Binary Coded Decimal (BCD)
Binary Coded Decimal (BCD) is a
method that uses binary digits 0 which represent “off” and 1 which represent
“on”. BCD has been in use since the first UNIVAC Computer. Each digit is called
a bit. Four bits are called a nibble and is used to represent each decimal
digit (0 through 9).
The first binary number system
was documented by Gottfried Leibniz in the 17th century. In 1854 mathematician
George Boole came up with a system of logic that is know today as Boolean
Algebra (based on two elements 0's and 1's).
The binary numbering system use a
base of 2 whereas the decimal numbering system use a base of 10. When the
binary number is 0, then the number is off, when the binary number is 1, then
the number is on. The configuration of BCD is "8421" a 4 bit binary
called a nibble . Therefore, the decimal 5 is a BCD 0101: where 0=8, 1=4, 0=2,
1=1; the 8 and 2 are turned off.
The following is an example of
binary digits and how they represent decimal digits:
Decimal BCD
0 0000
1 0001
2 0010
3 0011
4 0100
5 0101
6 0110
7 0111
8 1000
9 1001
The advantage that Binary Coded
Decimal (BCD) has over Binary is that there is no limit to number size. For
every decimal number added, you add 4-bits or one nibble. Binary numbers are
limited to the largest number that can be represented by 8, 16, 32 and 64 bits.
It is easier to convert decimal numbers to and from BCD than Binary. BCD is
usually converted to Binary for arithmetic processing since computers only
process 0’s and 1’s. However, hardware can be built to operate directly with
BCD. BCD is common in electronic systems where numeric value is displayed. This
is done in systems that consist of digital logic and do not contain a
microprocessor.
Computer processing requires a
minimum of 1 byte (8 bits) therefore; the left portion of each BCD number is
wasted storage. Because storage is valuable, storage can be saved by using
packed BCD numbers. With packed BCD numbers (e.g. 2 bytes are use to store 3484
instead of 4 bytes) the left byte will consist of 00110100 (34) the right byte
will consist of 10000100 (84).
Computer Chip
A computer chip is a small
electronic circuit, also known as an integrated circuit, which is one of the
basic components of most kinds of electronic devices, especially computers.
Computer chips are small and are made of a semiconductor that is usually
composed of silicon, on which several tiny components including transistors are
embedded and used to transmit electronic data signals. They became popular in
the latter half of the 20th century because of their small size, low cost, high
performance and ease to produce.
The modern computer chip saw its
beginning in the 1950s through two separate researchers who were not working
together, but developed similar chips. The first was developed at Texas
Instruments by Jack Kilby in 1958, and the second was developed at Fairchild
Semiconductor by Robert Noyce in 1958. These first computer chips used
relatively few transistors, usually around ten, and were known as small-scale
integration chips. As time went on through the century, the amount of
transistors that could be attached to the computer chip increased, as did their
power, with the development of medium-scale and large-scale integration
computer chips. The latter could contain thousands of tiny transistors and led
to the first computer microprocessors.
There are several basic
classifications of computer chips, including analog, digital and mixed signal
varieties. These different classifications of computer chips determine how they
transmit signals and handle power. Their size and efficiency are also dependent
upon their classification, and the digital computer chip is the smallest, most
efficient, most powerful and most widely used, transmitting data signals as a
combination of ones and zeros.
Today, large-scale integration
chips can actually contain millions of transistors, which is why computers have
become smaller and more powerful than ever. Not only this, but computer chips
are used in just about every electronic application including home appliances,
cell phones, transportation and just about every aspect of modern living. It
has been posited that the invention of the computer chip has been one of the
most important events in human history. The future of the computer chip will
include smaller, faster and even more powerful integrated circuits capable of
doing amazing things, even by today’s standards.
Automated Teller Machine
ATM is a banking terminal that
accepts deposits and dispenses cash. ATMs are activated by inserting a cash or
credit card that contains the user's account number and PIN on a magnetic
stripe. The ATM calls up the bank's computers to verify the balance, dispenses
the cash and then transmits a completed transaction notice. The word
"machine" in the term "ATM machine" is certainly redundant,
but widely used.
Advantages of Automated Teller
Machines:
- ATM provides 24 hours service
- ATM gives convenience to bank's customers
- ATM reduces the workload of bank's staff
- ATM provide service without any error
- ATM is very beneficial for travelers
- ATM may give customers new currency notes
- ATM provides privacy in banking transactions
Functions of ATM Machine
- Withdrawals
- Deposits
- Balance Inquiries
- Account transfer
- Utility bill pay (i.e. Cell phone recharge)
- Mini Statement Printing
P-N Junction
One of the crucial keys to solid
state electronics is the nature of the P-N junction. When p-type and n-type
materials are placed in contact with each other, the junction behaves very
differently than either type of material alone. Specifically, current will flow
readily in one direction (forward biased) but not in the other (reverse
biased), creating the basic diode. This non-reversing behavior arises from the
nature of the charge transport process in the two types of materials.
Fig: A p–n junction. The circuit
symbol is shown: the triangle corresponds to the p side.
p–n junctions are elementary
"building blocks" of most semiconductor electronic devices such as
diodes, transistors, solar cells, LEDs, and integrated circuits; they are the
active sites where the electronic action of the device takes place. For
example, a common type of transistor, the bipolar junction transistor, consists
of two p–n junctions in series, in the form n–p–n or p–n–p.
Local-Area Network (LAN)
A local area network (LAN) is a
computer network that interconnects computers in a limited area such as a home,
school, computer laboratory, or office building using network media. They function
to link computers together and provide shared access to printers, file servers,
and other services. LANs in turn may be plugged into larger networks, such as
larger LANs or wide area networks (WANs), connecting many computers within an
organization to each other and/or to the Internet.
Because the technologies used to
build LANs are extremely diverse, it is impossible to describe them except in
the most general way. Universal components consist of the physical media that
connect devices, interfaces on the individual devices that connect to the
media, protocols that transmit data across the network, and software that
negotiates, interprets, and administers the network and its services. Many LANs
also include signal repeaters and bridges or routers, especially if they are
large or connect to other networks.
Major Characteristics of LAN
- Every computer has the potential to communicate with any other computers of the network
- High degree of interconnection between computers
- Easy physical connection of computers in a network
- Inexpensive medium of data transmission
- High data transmission rate
Use of LAN
Followings are the major areas
where LAN is normally used
- File transfers and Access
- Word and text processing
- Electronic message handling
- Remote database access
- Personal computing
- Digital voice transmission and storage
Advantages of LAN
- Files can be stored on a central computer (the file server) allowing data to be shared throughout an organization.
- Workstations can share peripheral devices like printers. This is cheaper than buying a printer for every workstation.
- Networks also allow security to be established, ensuring that the network users may only have access to certain files and applications.
- Software and resources can be centrally managed.
- Network versions of software often allow for their speedy installation on workstations from the file server.
- Workstations do not necessarily need their own hard disk or CD-ROM drives which make them cheaper to buy than stand-alone PCs. Users can save their work centrally on the network file server. This means that they can retrieve their work from any workstation on the network. They do not need to go back to the same workstation all the time.
- The reliability of network is high because the failure of one computer in the network does not effect the functioning for other computers.
- Addition of new computer to network is easy
- High rate of data transmission is possible
Disadvantages
- If the communication line fails, the entire network system breaks down.
- Special security measures are needed to stop users from using programs and data that they should not have access to.
- Networks are difficult to set up and need to be maintained by skilled technicians.
- If the file server develops a serious fault, all the users are affected, rather than just one user in the case of a stand-alone machine.
- Wired systems cannot be used in listed buildings.
- A fault in the network can cause user to lose the data
- It is difficult to make the system secure from hackers, novices or industrial espionage
- Decisions on resource planning tend to become centralized.
- Networks that have grown with little thought can be inefficient in the long term.
- As traffic increases on a network the performance degrades unless it is designed properly.
- The larger the network becomes difficult to manage
Wide Area Network
A Wide Area Network (WAN) is a
network that covers a broad area (i.e., any telecommunications network that
links across metropolitan, regional, or national boundaries) using private or
public network transports. Business and government entities utilize WANs to
relay data among employees, clients, buyers, and suppliers from various
geographical locations. In essence, this mode of telecommunication allows a
business to effectively carry out its daily function regardless of location.
The Internet can be considered a WAN as well, and is used by businesses,
governments, organizations, and individuals for almost any purpose imaginable.
Numerous WANs have been
constructed, including public packet networks, large corporate networks,
military networks, banking networks, stock brokerage networks, and airline
reservation networks. Some WANs are very extensive, spanning the globe, but
most do not provide true global coverage.
Advantages of WAN
- Covers a large geographical area so long distance businesses can connect on the one network
- Shares software and resources with connecting workstations
- Messages can be sent very quickly to anyone else on the network. These messages can have pictures, sounds, or data included with them (called attachments).
- Expensive things (such as printers or phone lines to the internet) can be shared by all the computers on the network without having to buy a different peripheral for each computer.
- Everyone on the network can use the same data. This avoids problems where some users may have older information than others.
- Share information/files over a larger area
- Large network cover
Disadvantages of WAN
- Expensive and generally slow
- Need a good firewall to restrict outsiders from entering and disrupting the network
- Setting up a network can be an expensive and complicated experience. The bigger the network the more expensive it is.
- Security is a real issue when many different people have the ability to use information from other computers. Protection against hackers and viruses adds more complexity and expense.
- Once set up, maintaining a network is a full-time job which requires network supervisors and technicians to be employed.
- Information may not meet local needs or interests
- Vulnerable to hackers or other outside threats
Metropolitan Area Network
Metropolitan Area Network (MAN)
is a computer network usually spanning a campus or a city, which typically
connect a few local area networks using high speed backbone technologies. A MAN
often provides efficient connections to a wide area network (WAN). There are
three important features which discriminate MANs from LANs or WANs:
- The network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km range. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings.
- A MAN (like a WAN) is not generally owned by a single organisation. The MAN, its communications links and equipment are generally owned by either a consortium of users or by a network service provider who sells the service to the users.
- A MAN often acts as a high speed network to allow sharing of regional resources. It is also frequently used to provide a shared connection to other networks using a link to a WAN.
Central Processing
Unit (CPU)
At the “heart” of every computer
lies the CPU, or central processing unit, which is responsible for carrying out
arithmetic and logic functions as well as executing instructions to other
components. The components of a CPU work together, and depending on how they
are made, determine exactly how fast these operations can be carried out along
with how complex the operations can be. Each of the separate components of a
CPU on their own is relatively simple. Some of the primary components of a CPU,
also known as a microprocessor, are the arithmetic logic unit (ALU), the
control unit and the registers.
To begin with, the arithmetic
logic unit is the part of the CPU that, as its name implies, carries out the
mathematical functions of addition, subtraction, multiplication and division.
It is often thought that these functions are all the CPU does in a computer,
but this is not true. The ALU works along with, and as a major part of, the
other components of a CPU to run many complex processes. A CPU can contain more
than one arithmetic logic unit, and these ALUs can also be used for the purpose
of maintaining timers that help run the computer.
The control unit is another
fundamental part of the CPU. Essentially, it regulates the flow of information
through the processor. The functions that a control unit performs can vary
based on what a particular CPU was built to do. Mostly, this component
receives, decodes, stores results and manages execution of data that flows
through the CPU. More complex control units need to schedule when and how this
great amount of information is to be processed and make sure that the data is
sent to the correct components of the computer.
More components of a CPU that are
vital to its operation are the registers, which are very small memory locations
that are responsible for holding the data that is to be processed. The most
important of these registers is known as the instruction pointer, which directs
the CPU to the next memory location from where it is to receive information.
Another type of register is the accumulator, which is responsible for storing
the next values that will be processed by the CPU. Together all of these
components of a CPU are becoming faster, more compact and more powerful as time
goes on and technology advances.
EBCDIC
EBCDIC (Extended Binary Coded
Decimal Information Code) is an eight-bit character set that was developed by
International Business Machines (IBM). It was the character set used on most
computers manufactured by IBM prior to 1981. EBCDIC is not used on the IBM PC
and all subsequent "PC clones". These computer systems use ASCII as
the primary character and symbol coding system.
EBCDIC is widely considered to be
an obsolete coding system, but is still used in some equipment, mainly in order
to allow for continued use of software written many years ago that expects an
EBCDIC communication environment. It is the code for text files that is used in
IBM's OS/390 operating system for its S/390 servers and that thousands of
corporations use for their legacy applications and databases. In an EBCDIC
file, each alphabetic or numeric character is represented with an 8-bit binary
number (a string of eight 0's or 1's). 256 possible characters (letters of the alphabet,
numerals, and special characters) are defined.
MICR
Magnetic ink character
recognition, or MICR, is a character recognition technology used primarily by
the banking industry to facilitate the processing and clearance of cheques and
other document. The MICR encoding, called the MICR line, is located at the
bottom of a cheque or other voucher and typically includes the document type
indicator, bank code, bank account number, cheque number and the amount, plus
some control indicator. The technology allows MICR readers to scan and read the
information directly into a data collection device. Unlike barcodes or similar
technologies, MICR characters can be easily read by humans.
The use of MICR can enhance
security and minimize the losses caused by some types of crime. If a document
has been forged - for example, a counterfeit check produced using a color
photocopying machine, the magnetic-ink line will either not respond to magnetic
fields, or will produce an incorrect code when scanned using a device designed
to recover the information in the magnetic characters. Even a legitimate check
can be rejected if the MICR reader indicates that the owner of the account has
a history of writing bad checks.
