📑 Topics on this page (Jump to Topic):
📌 1. CPU (Central Processing Unit)
- The CPU is called the brain of the computer. Today the CPU is on a single chip — the microprocessor.
- Three parts of the CPU: ALU, CU and Registers/Memory unit.
| Part | Function |
|---|---|
| ALU (Arithmetic Logic Unit) | Arithmetic (+ − × ÷) and logical (AND, OR, comparison) operations |
| CU (Control Unit) | Controls all parts; fetches and decodes instructions — the "manager" of the computer |
| Registers | Fastest and smallest memory, inside the CPU |
| Register | Function |
|---|---|
| PC (Program Counter) | Holds the address of the next instruction |
| IR (Instruction Register) | Holds the current instruction |
| MAR | Holds the memory address |
| MBR / MDR | Holds data coming from/going to memory |
| Accumulator | Holds intermediate ALU results |
- Machine cycle: Fetch → Decode → Execute → Store.
- CPU speed is measured in Hertz (GHz). Multi-core = several processor cores on one chip.
- GPU = Graphics Processing Unit (images/video, AI computation).
⚠️ Exam Traps:
- The Program Counter holds the address of the next instruction, not the instruction itself.
- Comparison is done by the ALU, not the CU.
📌 2. Motherboard, Bus & Ports
- The motherboard is the main circuit board holding the CPU, RAM, chipset and slots.
- SMPS converts AC into DC for the computer. A UPS gives backup when power fails.
- The CMOS battery keeps date-time and BIOS settings.
- The system bus has three parts: data bus (bidirectional), address bus (unidirectional), control bus.
| Port | Use |
|---|---|
| USB (Universal Serial Bus) | Pen drive, mouse, printer — plug and play |
| HDMI | Audio + high-definition video |
| VGA | Older monitors (analog video) |
| RJ-45 | Ethernet / LAN cable |
| RJ-11 | Telephone line |
| Serial / Parallel | Old mouse-modem / old printers |
⚠️ Exam Traps:
- The data bus is bidirectional; the address bus is unidirectional (CPU to memory).
- LAN cable = RJ-45; telephone = RJ-11.
📌 3. Input Devices
| Device | Fact |
|---|---|
| Keyboard | QWERTY layout (Christopher Sholes); usually 104 keys |
| Mouse | Pointing device; Douglas Engelbart (1960s) |
| Scanner | Converts paper images/text to digital form |
| OCR | Reads printed characters into editable text |
| OMR | Reads marks/bubbles on OMR sheets (exams) |
| MICR | Reads magnetic ink at the bottom of cheques (banks) |
| Barcode Reader | Reads product barcodes (shops) |
| Light Pen, Joystick, Touch screen, Webcam, Microphone, Biometric | Other input devices |
⚠️ Exam Traps:
- Cheque = MICR; OMR answer sheet = OMR; printed text = OCR.
- A touch screen is both input and output.
📌 4. Output Devices
| Device | Fact |
|---|---|
| Monitor (VDU) | Soft copy; CRT, LCD, LED, OLED; resolution = number of pixels |
| Impact Printer | Prints by striking paper — dot matrix, daisy wheel, line printer |
| Non-impact Printer | Without striking — inkjet, laser, thermal |
| Plotter | Large maps/engineering drawings |
| Speaker, Projector, Headphone | Other outputs |
- Printer speed: dot matrix — CPS, line printer — LPM, laser — PPM (pages per minute).
- Hard copy = output on paper; soft copy = on screen.
- Pixel = smallest dot on screen; dpi = print quality.
⚠️ Exam Traps:
- A laser printer is non-impact; dot matrix is impact.
- A plotter is an output device, not input.
📌 5. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. Which is called the "brain" of the computer? Practice
Correct answer: (B)
The CPU does all calculations and control, so it is called the brain.
The CPU does all calculations and control, so it is called the brain.
Q2. Which part of the CPU performs comparisons and logical operations? Practice
Correct answer: (C)
ALU = Arithmetic Logic Unit — both arithmetic and logical operations.
ALU = Arithmetic Logic Unit — both arithmetic and logical operations.
Q3. Which part decodes instructions and controls all other parts? Practice
Correct answer: (D)
The Control Unit fetches and decodes instructions and sends control signals.
The Control Unit fetches and decodes instructions and sends control signals.
Q4. What does the Program Counter (PC) hold? Practice
Correct answer: (A)
The PC holds the memory address of the next instruction; the current instruction is in the IR.
The PC holds the memory address of the next instruction; the current instruction is in the IR.
Q5. CPU clock speed is measured in: Practice
Correct answer: (B)
Modern CPU speed is in GHz (gigahertz).
Modern CPU speed is in GHz (gigahertz).
Q6. Which technology is used by banks to read cheques? Practice
Correct answer: (C)
MICR = Magnetic Ink Character Recognition — magnetic ink characters on cheques.
MICR = Magnetic Ink Character Recognition — magnetic ink characters on cheques.
Q7. Which device is used to check the bubbles on competitive-exam answer sheets? Practice
Correct answer: (D)
OMR = Optical Mark Reader — reads pen/pencil marks.
OMR = Optical Mark Reader — reads pen/pencil marks.
Q8. Which of these is both an input and an output device? Practice
Correct answer: (A)
A touch screen takes touch (input) and displays images (output).
A touch screen takes touch (input) and displays images (output).
Q9. Which of these is a non-impact printer? Practice
Correct answer: (B)
A laser printer prints with toner and laser and does not strike the paper.
A laser printer prints with toner and laser and does not strike the paper.
Q10. Which output device prints large maps and engineering drawings? Practice
Correct answer: (C)
A plotter produces large, precise line drawings.
A plotter produces large, precise line drawings.
Q11. Laser printer speed is usually measured in: Practice
Correct answer: (D)
PPM = pages per minute. Dot matrix = CPS, line printer = LPM.
PPM = pages per minute. Dot matrix = CPS, line printer = LPM.
Q12. Which connector is used for a LAN (Ethernet) cable? Practice
Correct answer: (A)
RJ-45 is for Ethernet; RJ-11 is for telephone.
RJ-45 is for Ethernet; RJ-11 is for telephone.
Q13. Which port sends high-definition video and audio over one cable? Practice
Correct answer: (B)
HDMI = High-Definition Multimedia Interface.
HDMI = High-Definition Multimedia Interface.
Q14. Which bus is bidirectional? Practice
Correct answer: (C)
Data moves both ways between CPU and memory; addresses are sent only from the CPU.
Data moves both ways between CPU and memory; addresses are sent only from the CPU.
Q15. What is the main function of the SMPS? Practice
Correct answer: (D)
The SMPS supplies the required DC voltages to computer parts.
The SMPS supplies the required DC voltages to computer parts.
Q16. The QWERTY keyboard layout is named after: Practice
Correct answer: (A)
The top letter row begins Q-W-E-R-T-Y.
The top letter row begins Q-W-E-R-T-Y.
Q17. Who invented the computer mouse? Practice
Correct answer: (B)
Douglas Engelbart invented the mouse in the 1960s.
Douglas Engelbart invented the mouse in the 1960s.
Q18. The technology that converts a printed document into editable text is: Practice
Correct answer: (C)
OCR = Optical Character Recognition.
OCR = Optical Character Recognition.
Q19. The smallest dot of an image on the screen is called: Practice
Correct answer: (D)
Pixel = picture element. More pixels = higher resolution.
Pixel = picture element. More pixels = higher resolution.
Q20. What keeps BIOS settings and the system clock when power is off? Practice
Correct answer: (A)
A small CMOS battery on the motherboard keeps this information.
A small CMOS battery on the motherboard keeps this information.