Computer Science important questions

Block diagram of a computer system:

        +-------------+       +----------------------+       +-------------+
Input ->| Input Unit  | ----> |   Central Processing |----> | Output Unit | -> Output
        +-------------+       |     Unit (CPU)       |       +-------------+
                              |  +----------------+  |
                              |  | Control Unit   |  |
                              |  | ALU            |  |
                              |  | Registers      |  |
                              |  +----------------+  |
                              +----------+-----------+
                                         |
                                  +------v------+
                                  | Memory Unit |
                                  +-------------+

Input unit: The input unit is used to feed data and instructions into the computer. Input devices such as the keyboard, mouse, scanner and microphone accept information from the user, convert it into a binary (machine readable) form and send it to the CPU or memory for processing. Thus the input unit forms the entry point of data into the system.

Processing unit (CPU): The CPU, called the brain of the computer, processes the data supplied by the input unit. It has three parts:

• Arithmetic and Logic Unit (ALU): performs all arithmetic operations (addition, subtraction) and logical operations (comparison, AND, OR).
• Control Unit (CU): fetches, decodes and executes instructions and generates control signals to coordinate all units.
• Registers: small, high speed storage locations inside the CPU that temporarily hold data and instructions during processing. Together these parts carry out the actual processing that turns input data into meaningful output.

Computer architecture is the design of a computer system as seen by the programmer, including the instruction set, data types, addressing modes and registers (the logical, functional view of what the computer does). Computer organization deals with how the architecture is implemented in hardware, such as the control signals, interconnections and memory technology (the physical view of how it works).

Units of a computer system (block diagram):

        +-------------+       +----------------+       +-------------+
Input ->| Input Unit  | ----> |      CPU       | ----> | Output Unit | -> Output
        +-------------+       |  (ALU + CU +   |       +-------------+
                              |   Registers)   |
                              +-------+--------+
                                      |
                                +-----v------+
                                | Memory Unit|
                                +------------+

• Input unit: accepts data and instructions from input devices and converts them into machine form.
• CPU: the brain that processes data; it contains the ALU (arithmetic and logical operations), the Control Unit (directs and coordinates all operations) and registers (fast temporary storage).
• Memory unit: stores data, instructions and results, both primary (RAM, ROM) and secondary storage.
• Output unit: converts processed results into human readable form and sends them to output devices.

The arrows show the flow of data (solid) and control signals from the CPU to all units.

Memory is the part of a computer that stores data, instructions and results either temporarily or permanently. It is measured in bytes, KB, MB, GB and so on. Types of memory: 1. Primary (main) memory - directly accessible by the CPU, hol...

Computer architecture refers to the design and the attributes of a computer system that are visible to a programmer, such as the instruction set, addressing modes, data types and the logical design (the what and why). Computer organizati...

Difference between analog and digital computer:

ROM (Read Only Memory) is a non volatile primary memory whose contents can normally only be read and not written by the user during operation. It retains its data even when the power is switched off and usually stores permanent instructions such as the BIOS/bootstrap program needed to start the computer.

Different types of ROM:

• PROM (Programmable ROM): blank when made, can be programmed once by the user, after which it cannot be changed.
• EPROM (Erasable Programmable ROM): can be erased by exposing it to ultraviolet light and then reprogrammed.
• EEPROM (Electrically Erasable Programmable ROM): can be erased and reprogrammed electrically, byte by byte, without removing it from the computer.
• Mask ROM: programmed with data permanently by the manufacturer at the time of production.

Secondary memory (auxiliary storage) is non volatile memory used to store data, programs and information permanently. It is not directly accessed by the CPU, has a large capacity, is cheaper and slower than primary memory, and keeps its data even when the power is off. Examples: hard disk, CD/DVD, pen drive, SSD.

Hard disk: A hard disk (Hard Disk Drive, HDD) is the main secondary storage device of a computer. It consists of one or more rigid circular metal platters coated with a magnetic material, mounted on a spindle that rotates at high speed. Data is stored magnetically in concentric tracks and sectors, and read/write heads move across the surfaces to read or record data. Key points:

• Large storage capacity (measured in GB and TB).
• Non volatile, so data is retained permanently.
• Faster than optical disks but slower than SSD and RAM.
• Used to store the operating system, software and user files.

a. URL (Uniform Resource Locator) A URL is the unique address of a resource (web page, image or file) on the Internet that tells the browser where the resource is located and how to fetch it. A typical URL has the form: https://www.example.com/page.html It consists of the protocol (https), the domain name (www.example.com) and the path/file name (/page.html). By typing a URL or clicking a link, the browser locates and displays the correct web page.

b. Mobile computing Mobile computing is the technology that lets users transmit data, voice and video and access information through portable wireless devices (smartphones, tablets, laptops) without being tied to a fixed physical connection. It relies on wireless networks such as Wi-Fi and mobile data (4G/5G). Its benefits include mobility, anytime anywhere access, real time communication and location based services, which is why it is widely used for banking, e-learning, navigation and social media.

Fourth generation computers (1971 onwards) use the microprocessor, a single silicon chip that contains the whole CPU, built with VLSI (Very Large Scale Integration) technology. Main characteristics: - Technology: microprocessor (LSI/VLSI...

Memory is the storage part of a computer that holds data, instructions and results temporarily or permanently. Four differences between primary and secondary memory: Primary memory Secondary memory ------ Directly accessed by the CPU Not...

Mobile computing is the technology that allows people to transmit data, voice and video and access information through portable wireless devices without being connected to a fixed physical link. Why it is becoming more popular: - Mobilit...

a. Cache memory Cache memory is a small, very fast memory placed between the CPU and the main memory (RAM). It stores copies of the data and instructions that the CPU uses most frequently, so the processor can fetch them quickly instead ...

Major features of mobile computing: - Portability / mobility: devices are small and can be carried and used anywhere. - Wireless connectivity: connects to networks through Wi-Fi, mobile data, Bluetooth without cables. - Anytime, anywhere...

The CPU (Central Processing Unit) is the brain of the computer that carries out instructions of a program. Its main functions are: - Fetch: it fetches (reads) instructions and data from main memory one by one. - Decode: the control unit ...

Fourth generation computers (1971 onwards) are based on the microprocessor, which is a single chip containing the entire CPU built using VLSI (Very Large Scale Integration) technology. Features: - Component: microprocessor (LSI and VLSI ...

A non-impact printer produces characters and images on paper without the print mechanism striking the paper. It uses techniques such as spraying ink, laser and toner, or heat, so it works quietly and gives high quality output. Features: ...

a. OCR (Optical Character Recognition) OCR is a technology and input device that scans printed or handwritten text and converts it into machine editable text (character codes) that the computer can process. The OCR device reads the shape...

Memory is the part of a computer that stores data, instructions and results either temporarily or permanently so that they can be processed and retrieved when needed. Difference between SRAM and DRAM: SRAM (Static RAM) DRAM (Dynamic RAM)...

Importance of mobile computing: Mobile computing is the technology that allows transmission of data, voice and video through a computer or any wireless device without connecting to a fixed physical link. - Mobility: users can access info...

Difference between second and third generation computers: Second generation (1959-1965) Third generation (1965-1971) ------ Used transistors as the main electronic component Used integrated circuits (ICs) Larger in size than third genera...

A non-impact printer prints characters and images without the print head physically striking the paper. Instead it uses heat, laser beams or sprayed ink, so it is quiet, fast and gives high quality output. Characteristics: - No mechanica...

a. Bar Code Reader A bar code reader (bar code scanner) is an input device that reads bar codes, which are patterns of parallel black and white lines of varying widths printed on products. It shines a light on the bar code, and a light s...

Boolean algebra is a branch of mathematics that deals with variables having only two possible values, $0$ (false/low) and $1$ (true/high), and with logical operations (AND, OR, NOT) performed on them. It is the mathematical foundation used to design and simplify digital logic circuits.

AND gate The AND gate gives output $1$ only when all inputs are $1$. Boolean expression: $Y = A \cdot B$. Logic symbol: a D-shaped body with a flat input side and two inputs $A$, $B$.

Venn diagram: two overlapping circles $A$ and $B$; only the intersection (overlap) region is shaded, representing $A \cdot B$.

NAND gate The NAND gate is an AND gate followed by a NOT gate; its output is $0$ only when all inputs are $1$, and $1$ otherwise. Boolean expression: $Y = \overline{A \cdot B}$. Logic symbol: an AND gate symbol with a small bubble (circle) at the output.

Venn diagram: two overlapping circles $A$ and $B$; everything except the intersection is shaded, representing $\overline{A \cdot B}$.

A logic gate is a basic digital circuit that produces a single binary output from one or more binary inputs according to a logical rule. Five common gates are described below. 1. AND gate - output $1$ only when all inputs are $1$. $Y = A...

A logic gate is a fundamental digital circuit that takes one or more binary inputs and produces one binary output ($0$ or $1$) according to a definite logical rule. Gates are the building blocks of all digital electronic systems. 1. AND ...