Unit 1: Computer Fundamentals - Subjective Questions

A computer is an electronic programmable device that accepts data as input, processes it according to a set of instructions, stores it, and produces meaningful information as output.

Major characteristics include:

• Speed: A computer can execute millions or billions of instructions per second.
• Accuracy: It produces accurate results when the data and instructions supplied are correct.
• Diligence: It can perform repetitive tasks continuously without becoming tired or losing concentration.
• Storage capacity: It can store large amounts of data and retrieve them quickly.
• Automation: Once a program is started, the computer can complete the assigned work automatically.
• Versatility: It can perform different types of tasks, such as calculations, document preparation, communication, and multimedia processing.
• Reliability: It can consistently produce the same result for the same data and instructions.
• Multitasking: Modern computers can run several programs at the same time.

A computer has no intelligence or emotions of its own; it works only according to the instructions given to it.

Although computers are powerful, they have several limitations:

• Lack of intelligence: A computer cannot think, reason, or make judgments like a human unless rules have been programmed into it.
• Dependence on instructions: It performs only the operations specified by a program.
• No emotions or common sense: It cannot naturally understand feelings, social situations, or practical circumstances.
• Garbage In, Garbage Out: Incorrect input or instructions produce incorrect output. This principle is commonly called GIGO.
• Dependence on electricity and hardware: A computer cannot operate without power and functioning components.
• Security risks: Stored data may be damaged, stolen, or misused by malware or unauthorized users.
• Limited independent decision-making: Even artificial intelligence systems operate within the limits of their data, algorithms, and training.

Therefore, a computer is an efficient tool, but human involvement is necessary to provide correct data, instructions, interpretation, and control.

The development of computers is commonly divided into five generations:

1. First generation:

   • Period: approximately 1940–1956
   • Main technology: vacuum tubes
   • Programming: machine language
   • Features: very large, expensive, slow, and power-consuming; generated considerable heat
   • Examples: ENIAC and UNIVAC I

2. Second generation:

   • Period: approximately 1956–1963
   • Main technology: transistors
   • Programming: assembly language and early high-level languages such as FORTRAN and COBOL
   • Features: smaller, faster, more reliable, and less power-consuming than first-generation computers

3. Third generation:

   • Period: approximately 1964–1971
   • Main technology: integrated circuits, or ICs
   • Features: improved speed, reliability, storage, and operating systems; keyboards and monitors became common
   • Example: IBM System/360

4. Fourth generation:

   • Period: from approximately 1971 onward
   • Main technology: microprocessors, using VLSI technology
   • Features: personal computers, graphical interfaces, networking, compact size, and low cost
   • Examples: IBM PC and Apple Macintosh

5. Fifth generation:

   • Period: present and continuing
   • Main technology: ULSI, parallel processing, and artificial intelligence
   • Features: natural-language processing, robotics, machine learning, expert systems, and intelligent applications

Each generation represents major improvements in size, cost, speed, storage capacity, reliability, and ease of use.

First-generation and fourth-generation computers differ in the following ways:

Thus, the replacement of vacuum tubes by microprocessors made computers smaller, faster, cheaper, and more reliable.

A simplified functional block diagram is:

Input Unit → Memory Unit ↔ CPU → Output Unit

The CPU contains the Control Unit, Arithmetic and Logic Unit, and registers. Secondary storage exchanges data with memory when required.

Functions of the blocks

• Input unit: Accepts data and instructions from devices such as a keyboard, mouse, scanner, or microphone. It converts them into a machine-readable form.
• Memory unit: Stores programs, input data, intermediate results, and output. Primary memory includes RAM and ROM.
• Control Unit: Directs and coordinates all computer operations. It fetches and decodes instructions and sends control signals to other components.
• Arithmetic and Logic Unit: Performs arithmetic operations such as addition and subtraction and logical operations such as comparison and Boolean operations.
• Registers: Provide very fast temporary storage inside the CPU for instructions, addresses, and intermediate results.
• Output unit: Converts processed results into a form understandable to users through devices such as monitors, printers, and speakers.
• Secondary storage: Stores programs and data permanently or for long periods using devices such as SSDs and hard disks.

Basic working cycle

1. Data and instructions enter through the input unit.
2. They are placed in memory.
3. The CPU fetches, decodes, and executes the instructions.
4. Intermediate or final results are stored in memory.
5. The output unit presents the final information to the user.

The Central Processing Unit, or CPU, is the main processing component of a computer. Its principal components are:

• Arithmetic and Logic Unit: Performs arithmetic calculations, comparisons, and logical operations.
• Control Unit: Coordinates the activities of the CPU, memory, input devices, and output devices.
• Registers: Small, high-speed storage locations within the CPU. Examples include the program counter, instruction register, accumulator, and memory address register.
• Cache: Very fast memory close to or within the CPU that keeps frequently used data and instructions.

The fetch-decode-execute cycle works as follows:

1. Fetch: The Control Unit obtains the next instruction from memory using the address stored in the program counter.
2. Decode: The instruction is interpreted to determine the required operation and operands.
3. Execute: The CPU performs the operation, often using the Arithmetic and Logic Unit.
4. Store: The result is written to a register or memory.
5. Repeat: The program counter identifies the next instruction, and the cycle continues.

This cycle is repeated at very high speed while a program is running.

The four units serve different purposes:

• Input unit:

  • Used to enter data and instructions into a computer.
  • Converts user input into machine-readable signals.
  • Examples: keyboard, mouse, scanner, webcam, and microphone.

• Output unit:

  • Presents processed information to the user.
  • Converts machine results into visual, printed, or audio form.
  • Examples: monitor, printer, projector, and speaker.

• Primary memory:

  • Directly accessible by the CPU.
  • Holds programs and data currently being processed.
  • RAM is generally volatile, while ROM is non-volatile.
  • Examples: RAM, ROM, and cache.

• Secondary storage:

  • Stores data and programs for long-term use.
  • Has a larger capacity but is generally slower than primary memory.
  • It is normally non-volatile.
  • Examples: SSD, hard disk, memory card, optical disc, and USB drive.

The main distinction is that input and output units handle communication, while primary memory and secondary storage retain data and programs.

Computers represent all data using binary digits, because electronic circuits can conveniently distinguish between two states, commonly represented by and .

• Bit: The smallest unit of data; it can be either or .
• Nibble: A group of bits.
• Byte: A group of bits. A byte can represent different patterns.
• Word: A group of bits processed by the CPU as one unit. Common word sizes are , , and bits.

Common forms of representation include:

• Numbers: Stored using binary notation. Signed integers may use two's-complement representation, while real numbers commonly use floating-point representation.
• Text: Characters are assigned numeric codes. ASCII uses codes for letters, digits, and symbols, while Unicode supports characters from many languages.
• Images: Represented as pixels, with binary values describing each pixel's color and brightness.
• Audio: Sound is sampled at regular intervals, and each sample is stored as a binary number.
• Video: Represented as a sequence of image frames, often combined with digital audio.

Thus, text, numbers, images, audio, and video are ultimately stored as patterns of bits.

A positional number system is a system in which the value of a digit depends on:

• the digit itself,
• its position in the number, and
• the base or radix of the number system.

For a number with base , positional values are powers of . A number can be expanded as:

Digits to the right of the radix point use negative powers such as and .

For example:

Common radices are:

• Binary: base , using digits and
• Octal: base , using digits to
• Decimal: base , using digits to
• Hexadecimal: base , using digits to and to

The radix determines the permitted digits and the place values in the system.

The binary number system has base and uses only the digits and . Each position represents a power of .

The main binary addition rules are:

• , giving sum and carry
• , giving sum and carry

Aligning the numbers:

Therefore:

Verification in decimal:

Hence, the binary sum is .

To convert a decimal integer into binary, repeatedly divide it by and record each remainder:

Reading the remainders from bottom to top gives:

Verification:

Therefore, the required binary equivalent is .

To convert binary to decimal, multiply each digit by its positional power of .

For the integer part:

For the fractional part:

Combining both parts:

Therefore, the decimal equivalent is .

The octal number system has base and uses the digits through . Each octal position represents a power of .

To convert into decimal, expand it according to place value:

Therefore:

Octal notation is useful as a compact representation of binary because one octal digit corresponds exactly to three binary bits.

Binary and octal can be converted directly because . Therefore, each octal digit corresponds to exactly three binary bits.

To convert binary to octal:

1. Starting from the radix point, group binary digits into sets of three.
2. For an integer, group from right to left.
3. Add leading zeros if the leftmost group is incomplete.
4. Replace each group with its octal equivalent.

Given:

Add one leading zero and group the digits:

Convert each group:

Thus:

For octal-to-binary conversion, the process is reversed: replace each octal digit with its three-bit binary equivalent.

The hexadecimal number system has base . It uses the symbols to and the letters to , where:

To convert into decimal:

Therefore:

Hexadecimal is widely used in computing because one hexadecimal digit represents exactly four binary bits.

Binary and hexadecimal can be converted directly because . Thus, one hexadecimal digit corresponds to four binary bits.

Binary to hexadecimal

Group the binary number into sets of four from right to left:

Convert each group:

Therefore:

Hexadecimal back to binary

Replace each hexadecimal digit with four bits:

Combining the groups:

Hence, the hexadecimal equivalent is , and converting it back reproduces the original binary number.

To convert a decimal integer into octal, repeatedly divide the number by and record the remainders:

Reading the remainders from bottom to top gives:

Verification by place-value expansion:

Therefore, the correct octal equivalent is .

To convert decimal to hexadecimal, repeatedly divide by and record the remainders. Remainders from to are written as to .

Reading the remainders from bottom to top gives:

Verification:

Therefore, the hexadecimal equivalent is .

Octal to binary

Replace every octal digit with its three-bit binary equivalent:

Therefore:

Binary to hexadecimal

Group the binary digits into sets of four around the radix point. Add zeros where necessary:

Now convert each group:

Thus:

Octal to decimal

Use powers of :

Therefore:

The four major positional number systems can be compared as follows:

Uses in computing

• Binary: Used internally by digital computers because electronic circuits operate effectively with two states.
• Octal: Provides a shorter representation of binary. It has been used in older computer systems and in areas such as Unix-style file permissions.
• Decimal: Used for ordinary human calculations, data entry, measurement, and displaying results.
• Hexadecimal: Provides a compact representation of binary and is used for memory addresses, machine-code values, debugging, color codes, and low-level programming.

For example:

Binary is best suited to hardware, while octal and hexadecimal make long binary patterns easier for humans to read and write.