Computer Fundamentals

Memorize generations by their CORE switching technology: Gen-1 (1940-56) Vacuum Tubes; Gen-2 (1956-63) Transistors; Gen-3 (1964-71) Integrated Circuits (IC); Gen-4 (1971-present) Microprocessors/VLSI; Gen-5 (present-future) Artificial Intelligence/ULSI. Memory aid: 'Tubes Transform Into Micro AI' = T-T-I-M-A. Gen-1 used machine language and punch cards (ENIAC, UNIVAC); Gen-2 introduced assembly + COBOL/FORTRAN; Gen-3 brought keyboards, monitors, OS; Gen-4 gave us PCs/GUI/networks; Gen-5 focuses on parallel processing, quantum and natural language. SBI PO frequently asks 'which technology belongs to which generation' or matches examples (ENIAC=Gen1). Note: IC was invented by Jack Kilby; the microprocessor (Intel 4004) launched Gen-4.

By SIZE/POWER (descending): Supercomputer > Mainframe > Minicomputer > Microcomputer. Supercomputers (PARAM, CRAY, India's PARAM-Siddhi) use parallel processing for weather/research; Mainframes serve thousands of users (banking, census); Minicomputers (mid-range servers); Microcomputers = PCs/laptops/tablets. By DATA HANDLING: Analog (measures continuous data — speedometer, thermometer), Digital (discrete 0/1 data), Hybrid (both — ICU monitors, petrol pumps). Memory aid: Hybrid = 'measure + count'. SBI PO twist: ECG/ICU patient monitors are HYBRID (measure analog signals, display digital output). India's first supercomputer was PARAM 8000 (1991, C-DAC).

Exam-ready 'firsts' table: First electronic computer = ENIAC; First stored-program concept = EDVAC/EDSAC (von Neumann architecture); First commercial computer = UNIVAC-1; First microprocessor = Intel 4004 (4-bit); First PC = IBM PC (1981). India: First computer = HEC-2M / TIFRAC (first indigenous); First supercomputer = PARAM 8000. Father of Computer = Charles Babbage (Analytical Engine); Father of Modern Computer = Alan Turing; von Neumann = stored-program architecture. Memory aid for von Neumann components: 'CAMI' = Control, ALU, Memory, Input/Output. These are high-frequency one-mark factual questions in SBI PO Mains computer section.

From FASTEST/costliest/smallest to slowest/cheapest/largest: Registers > Cache > Primary (RAM) > Secondary (SSD/HDD) > Tertiary (optical/tape). Memory aid: 'Real Cats Run So Tirelessly'. As you move DOWN the hierarchy: speed decreases, cost-per-bit decreases, capacity increases. Registers sit inside the CPU; cache (L1<L2<L3, L1 fastest) bridges CPU-RAM speed gap. Primary memory is directly accessible by CPU and volatile (RAM); secondary is non-volatile and not directly accessed by CPU. SBI PO loves ordering questions — anchor on the rule: higher = faster + costlier + smaller. CPU can directly access only registers, cache, and RAM (primary), never secondary storage directly.

RAM (Random Access Memory) = volatile (data lost on power-off), read/write, working memory. Types: DRAM (needs constant refresh, used as main memory, cheap) and SRAM (no refresh, used as cache, fast/costly). ROM (Read Only Memory) = non-volatile, stores BIOS/firmware. ROM types: PROM (programmed once), EPROM (erased by UV light), EEPROM (electrically erasable — used in flash). Memory aid: 'EEPROM = Electrically Erasable'. Cache and RAM are volatile; ROM, HDD, SSD, flash are non-volatile. SBI PO trap: SRAM is faster than DRAM but DRAM is denser/cheaper. Flash memory (USB drives, SSD) is a type of EEPROM.

1 Byte = 8 bits. Ascending: KB < MB < GB < TB < PB < EB < ZB < YB, each step = 1024× (2^10) in binary or 1000× in decimal. Smallest unit = bit; Nibble = 4 bits; 1 Byte = 1 character (ASCII). Quick conversions: 1 KB = 1024 B, 1 MB = 1024 KB, 1 GB = 1024 MB. SBI PO numeric trick: to convert GB→MB multiply by 1024; MB→KB ×1024. Order mnemonic: 'Kind Men Give Tasty Pizza Every Zomato Year' = K M G T P E Z Y. ASCII uses 7 bits (128 chars), Extended ASCII 8 bits (256), Unicode 16 bits (65,536 chars) for global scripts including Hindi.

Binary (base-2, digits 0-1), Octal (base-8, 0-7), Decimal (base-10, 0-9), Hexadecimal (base-16, 0-9 then A-F where A=10...F=15). Memory aid: 'BODH' = Binary-Octal-Decimal-Hex with bases 2-8-10-16. Conversion shortcuts: every 3 binary digits = 1 octal digit; every 4 binary digits = 1 hex digit. So Binary→Octal: group bits in 3s; Binary→Hex: group in 4s (from right). Example: 11010110 → group as 1101|0110 = D6 hex; group as 011|010|110 = 326 octal. SBI PO computer section tests base conversion and digit-validity ('which is NOT a valid octal number'). Largest single hex digit F = 15 = 1111 binary.

To convert decimal→binary, repeatedly divide by 2 and read remainders BOTTOM to TOP. Faster exam trick: subtract powers of 2 (128,64,32,16,8,4,2,1). Example: 45 → 32+8+4+1 → mark positions: 128(0)64(0)32(1)16(0)8(1)4(1)2(0)1(1) = 00101101. Reverse (binary→decimal): multiply each bit by its positional power of 2 and sum. Example: 101101 = 32+8+4+1 = 45. Memorize powers of 2 up to 1024: 1,2,4,8,16,32,64,128,256,512,1024. SBI PO speed tip: for a string of n ones, value = 2^n − 1 (e.g., 11111 = 2^5−1 = 31). This saves seconds in conversion-heavy questions.

Basic gates: AND (output 1 only if ALL inputs 1), OR (1 if ANY input 1), NOT (inverter). Derived: NAND (NOT-AND), NOR (NOT-OR), XOR (1 if inputs DIFFER), XNOR (1 if inputs SAME). Memory aid: XOR = 'eXclusive — outputs 1 when inputs are unequal'. NAND and NOR are 'universal gates' — any circuit can be built from them alone. Truth-table quick recall for 2 inputs: AND=0001, OR=0111, XOR=0110 (for input pairs 00,01,10,11). SBI PO asks gate outputs and universal-gate identification. Boolean: A AND 0 = 0; A OR 1 = 1; A AND 1 = A; A OR 0 = A; NOT(NOT A) = A.

CPU (the 'brain') = Control Unit (directs operations, fetch-decode-execute) + ALU (arithmetic & logic) + Registers. Speed measured in Hertz/GHz; one instruction cycle = fetch-decode-execute-store. INPUT devices feed data IN: keyboard, mouse, scanner, microphone, OMR/OCR/MICR readers, joystick, light pen, barcode reader. OUTPUT devices give results OUT: monitor, printer, speaker, plotter, projector. Memory aid: 'In = sense the world, Out = show the result'. TRICKY dual devices: touchscreen and modem are BOTH input and output. MICR (Magnetic Ink Character Recognition) is used on bank cheques; OMR reads marked bubbles (exam answer sheets); OCR converts printed text to editable text. SBI PO frequently tests cheque-processing MICR.

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).