Information Technology Data Representation and Digital Logic, Exams of Information and Communications Technology (ICT)

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Information Technology

Data Representation and Digital Logic

Data Communication Devices

Modems ❖ In standard telephone service, a telephone converts the sound of your voice into an electric signal that flows through die telephone wires. ❖ The telephone at the other end converts this electric signal back into sound so that the person you are talking to can hear your voice. ❖ Both the sound wave and the telephone signal are analog signals, electrical waves that vary continuously with the volume and pitch of the speakers' voices. A computer’s “voice" is digital; that is, it consists of on/off pulses representing Is and Os. ❖ A device called a modem is needed to translate these digital signals into analog signals that can travel over standard telephone lines. ❖ In its modulation phase, the modem turns the computer’s digital signals into analog signals, which are then transmitted across the phone line.

dems An external modem ❖ An external modem is a box that houses the modem's circuitry outside the computer. ❖ It connects to the computer using a serial, USB, or FireWire port, and then connects to the telephone system with a standard telephone jack. An internal modem ❖ An internal modem is a circuit board that plugs into one of the computer's expansion slots. ❖ An internal modem saves desktop space but occupies an expansion slot. ❖ Modems also come in the form of a PC Card for use with laptop computers and with newer models, are likely to be built into the laptop appearing as a port in one of the sides. ❖ Some use standard telephone lines, but others include a cellular phone, which enables completely wireless transmissions. Fax mo ❖ Most modems used with personal computers also can emulate a fax machine. ❖ These devices can exchange faxes with any other fax modem or fax machine. ❖ With the proper software, users can convert incoming fax files into files that can be edited with a word processor—something that stand-alone fax machines cannot do.

Broadband Connections ❖ The term broadband is used to describe any data connection that can transmit data faster than is possible through a standard dial-up connection using a modem. ❖ Some of the better known are called integrated services digital network (ISDN), T l, T3, DSL, cable modems, and ATM. ❖ To get an understanding of the increments in bandwidth, you need to know that a basic rate integrated services digital network connection combines two 64 Kbps data channels and one 19 Kbps error-checking channel.

Wireless Adapter ❖ A PC or laptop needs a wireless adapter card (wireless NIC) that meets 802.11b or 802.1lg standards to make contact with the WAP. ❖ Many wireless NICs come with utility software that allows you to monitor signal strength and download speeds.

Data Representation in a Computer System Number Systems

❖ To a computer, everything is a number.

❖ Numbers are numbers; letters and punctuation marks are numbers; sounds and pictures are

numbers. Even the computer’s own instructions are numbers.

❖ When you see letters of the alphabet on a computer screen, you are seeing just one of the

computer's ways of representing numbers.

❖ In a computer, however; all data is represented by the state of the computer’s electronic

switches.

❖ A switch has only two possible states—on and off— so it can represent only two numeric

values.

❖ To a computer; when a switch is off, it represents a 0; when a switch is on, it represents a 1.

How Computer Process Data The CPU ❖ The CPU is the "brain” of the computer, the place where data is manipulated. ❖ In large computer systems, such as supercomputers and mainframes, processing tasks may be handled by multiple processing chips. ❖ In the average microcomputer the entire CPU is a single unit, called a microprocessor. ❖ Regardless of its construction, every CPU has at least two basic parts: the control unit and the arithmetic logic unit.

Character Representation Text Codes ❖ Early programmers realized that they needed a standard text code that was agreeable to all of them. ❖ In such a system, numbers would represent the letters of the alphabet, punctuation marks, and other symbols. ❖ This standard code system would enable any programmer or program to use the same combinations of numbers to represent the same individual pieces of data.

❖ The four most popular text code systems invented are the following: EBCDIC.

• EBCDIC stands for Extended Binary Coded Decimal Interchange Code.
• EBCDIC is an eight-bit code that defines 256 symbols. It is still used in IBM mainframe and midrange systems, but it is rarely encountered in personal computers.

Extended ASCII.

• Extended ASCII is an eight-bit code that specifies the characters for values from 128 to 255.
• The first 40 symbols represent pronunciation and special punctuation. The remaining symbols are graphic symbols.

Unicode.

• With four bytes, enough Unicode codes can be created to represent more than 4 billion different characters or symbols.
• One major advantage that Unicode has over other text code systems is its compatibility with ASCII codes.

Logic Gates and Boolean Functions

• Circuits which enable building of certain logical conditions using binary values and which enable making certain decisions, are called Logic Circuits.
• It is an electronic circuit having one or more than one input and only one output.
• There are two types of Logic gates.

▪ Basic Logic Gates

▪ Combinational Logic Gates

Basic Logic Gates

• There are three types of basic logic gates.
  • AND gate
  • OR gate
  • NOT gate