Hardware, Software & Operating Systems

Every device you have ever used — your phone, an ATM, a railway booking counter — runs on the same basic idea: something feeds data IN, a processor crunches it, and something shows the result OUT. Master that flow once and a whole bank of SBI PO computer-aptitude questions becomes nearly automatic.

Definition: The CPU (Central Processing Unit) is the part of a computer that actually executes instructions. It is often called the "brain" of the system.

Definition: An input device is any hardware that sends data or commands INTO the computer. An output device is any hardware that brings processed information OUT to the user.

Inside the CPU: three pieces working as one

The CPU is not a single mysterious chip — it is a small team with three distinct roles. The Control Unit (CU) is the manager: it does not perform calculations itself, it tells every other part what to do next. It runs the famous fetch–decode–execute cycle, pulling the next instruction from memory, working out what it means, and dispatching it. Some books extend this to fetch–decode–execute–store because the result usually has to be written back somewhere.

The ALU (Arithmetic and Logic Unit) is the calculator. Anything mathematical (addition, subtraction, multiplication) and anything logical (greater than, equal to, AND, OR, NOT) happens here. Without the ALU your CPU could only shuffle data around, never transform it.

Registers are tiny ultra-fast storage locations inside the CPU. They hold the data the ALU is currently working on, the address of the next instruction, and a few status flags. Registers are smaller and faster than RAM — that is why CPUs do not fetch from main memory for every step.

CPU speed is measured in Hertz (Hz), more commonly MHz (millions of cycles per second) or GHz (billions). A 3.0 GHz processor can in principle run three billion basic cycles each second. Exams sometimes ask the unit of "clock speed" — always Hertz, never bytes.

Input devices: how data enters the machine

Think of input devices as the senses of the computer. The familiar list is keyboard, mouse, scanner, microphone, joystick, light pen, barcode reader and the three reading machines that bankers love — OMR, OCR and MICR. The last three appear repeatedly in SBI PO because banks rely on them every day.

• MICR (Magnetic Ink Character Recognition) reads the funny-looking digits at the bottom of a bank cheque. The ink contains iron oxide so the reader picks up the pattern magnetically — almost impossible to forge with a photocopier. Every cheque-clearing centre in India runs on MICR.
• OMR (Optical Mark Recognition) detects darkened bubbles. JEE, NEET and SSC OMR sheets, employee feedback forms — anywhere you "fill in a circle" — uses OMR.
• OCR (Optical Character Recognition) turns printed or handwritten text into editable digital text. When you scan a page and the words become selectable, that is OCR at work.

Output devices: how results come out

The classic output team: monitor, printer, speaker, plotter, projector, headphones. A printer can be impact (dot-matrix), non-impact (inkjet, laser, thermal). A plotter draws large precise line graphics — used for architectural maps and engineering drawings, not ordinary text. Plotter vs printer is a common SBI PO trap; remember plotter = vector line drawings.

The tricky dual-role devices

A small but loved exam topic: devices that are BOTH input and output. The usual list is

• Touchscreen — your fingertip is input, the changing display is output.
• Modem — modulates outgoing signals and demodulates incoming ones.
• Headset (mic + earphones) — microphone is input, earphones are output.
• Network card — sends and receives.
• Hard disk / pen drive — you read FROM and write TO them.

If a question lists "touchscreen" or "modem" under "purely input devices", the option is wrong.

Why it matters: The CPU + I/O model is the single most tested foundation in the SBI PO computer-aptitude section. Five to seven marks every year hinge on remembering which device is input, which is output, and what MICR/OMR/OCR each do. Getting these right also helps you reason about descriptive questions in banking interviews where MICR codes and IFSC processing routinely come up.

Real-world example: When you deposit a cheque at your local SBI branch, the cheque is fed through a MICR reader. The branch computer captures the account and amount, sends it through the CTS (Cheque Truncation System), and the receiving bank's CPU executes the transaction — Control Unit fetching the credit instruction, ALU updating balances, output devices printing the slip you take home. Every step is the textbook diagram in motion.

Common misconception: Students often confuse "memory" with "registers" — they are not the same. RAM is system memory outside the CPU and is in megabytes/gigabytes. Registers live INSIDE the CPU and are typically only a few bytes each. Another frequent slip: thinking a "printer" can be an input device because it accepts data. It "receives data" only to display output — its job is to OUTPUT to paper, so it is purely an output device.

Question: Which of the following is correctly matched?
(a) MICR — Library cards
(b) OMR — Answer sheets
(c) OCR — Cheque clearing
(d) Plotter — Input device

Solution:
Step 1: MICR reads magnetic ink on cheques — not library cards. Eliminate (a).
Step 2: OCR converts printed text to editable text; cheque clearing is MICR. Eliminate (c).
Step 3: A plotter is an output device that draws line graphics. Eliminate (d).
Step 4: OMR reads filled bubbles on answer sheets — correct match.
Conclusion: Option (b).

SYSTEM software runs/manages the computer: Operating System, device drivers, utilities, language translators (compiler, interpreter, assembler). APPLICATION software does user tasks: MS Word/Excel, browsers, Tally, Photoshop, games. Memory aid: 'System serves the machine, Application serves the user'. Translators: Compiler (whole program at once → fast, shows all errors together — C, C++), Interpreter (line-by-line → slower, stops at first error — Python, BASIC), Assembler (assembly → machine code). Firmware = software embedded in hardware (BIOS). Utility software = antivirus, disk cleanup, backup. SBI PO trap: an Operating System is system software, NOT application; a compiler translates ENTIRE source code whereas an interpreter executes line by line.

OS = interface between user and hardware. Core FUNCTIONS: process management, memory management, file management, device/I-O management, security, user interface. TYPES: Batch (jobs grouped, no interaction), Time-sharing/Multitasking (many users/tasks share CPU via time slices), Real-Time OS (instant response — missiles, ATMs, medical; HARD vs SOFT RTOS), Distributed (multiple machines as one), Multiprocessing (multiple CPUs). Examples: Windows, Linux, macOS, Android (Linux-based), iOS, UNIX. Memory aid: 'RTOS = no delay tolerated'. Booting loads the OS into RAM; cold boot = power off→on, warm boot = restart without power-off. The kernel is the OS core managing resources. GUI (icons) vs CLI (command typing, e.g., MS-DOS, Linux terminal).

Cover the answer, recall, then check. 12 cards on hardware, software and operating systems.

Q1. Name the three parts of the CPU.
A1. ALU (Arithmetic Logic Unit), CU (Control Unit) and Registers. The CPU is called the "brain" of the computer.

Q2. Difference between system software and application software.
A2. System software runs the machine (OS, drivers, utilities, translators); application software does user tasks (MS Office, browsers).

Q3. Compiler vs Interpreter — key difference.
A3. A compiler translates the WHOLE program at once (reports all errors together); an interpreter translates and runs it line by line.

Q4. Give two examples each of input and output devices.
A4. Input: keyboard, mouse, scanner. Output: monitor, printer, speaker. (A touchscreen is both.)

Q5. What is an operating system and name three examples.
A5. System software that manages hardware and resources; e.g. Windows, Linux, macOS (also Unix, Android, iOS).

Q6. What is the kernel?
A6. The core of the operating system that directly manages memory, processes and hardware.

Q7. List four main functions of an OS.
A7. Process management, memory management, file management, device (I/O) management — plus security.

Q8. MICR, OMR and OCR — what does each read?
A8. MICR reads magnetic-ink characters (bank cheques); OMR reads marks (OMR answer sheets); OCR reads printed/handwritten text.

Q9. Difference between an assembler and a compiler.
A9. An assembler converts assembly language to machine code; a compiler converts a high-level language to machine code.

Q10. What is firmware and where is it stored?
A10. Permanent software that controls hardware, stored in ROM/flash (e.g. BIOS/UEFI).

Q11. Expand POST and BIOS.
A11. POST = Power-On Self-Test; BIOS = Basic Input/Output System (runs first at start-up).

Q12. Difference between GUI and CLI, with an example of each.
A12. GUI uses graphical icons (Windows); CLI uses typed commands (MS-DOS / Linux terminal).

Worked Example

Problem: Solved awareness question: Classify these as system software or application software — Windows OS, MS Word, Device Driver, Photoshop — and name two core functions of an operating system.

Solution:
System software runs and manages the computer itself; application software helps the user do specific tasks.
Windows OS — system software (operating system).
Device Driver — system software (lets the OS talk to hardware).
MS Word — application software (word processing).
Photoshop — application software (image editing).
Two core OS functions: managing hardware resources (CPU, memory, devices) and providing a user interface / managing processes and files.

Answer: Windows OS and Device Driver are system software; MS Word and Photoshop are application software. The OS manages resources and provides a user interface.