Computer Basics and Hardware — SSC CGL Computer Knowledge

The Computer Knowledge module is qualifying — its 60 marks don't count toward merit, but failing it voids everything else. The questions are deliberately basic: what does ALU stand for, which memory is volatile, how many MB in a GB. This chapter is the fact sheet; read it twice and the module is safe.

1. What SSC actually asks

Tier 2, Section III, Module I: ~10–13 of the 20 questions come from basics and hardware (the rest from MS Office, internet and security). Three marks each, −1 negative, qualifying threshold kept low. Question style is pure recall: full forms, "which of these is volatile", "brain of the computer", unit conversions.

2. Generations of computers

• Charles Babbage — "father of the computer" (Analytical Engine); Ada Lovelace — first programmer.
• India's fastest supercomputers are the PARAM and AIRAWAT families (C-DAC).

3. Inside the CPU

The CPU ("brain of the computer") has three parts:

• ALU — Arithmetic Logic Unit: all calculations and comparisons.
• CU — Control Unit: directs the fetch–decode–execute cycle; issues signals, does no math.
• Registers — tiny, fastest storage inside the CPU (accumulator, program counter).

Almost all machines follow von Neumann architecture: program and data share one memory, instructions execute via the fetch–decode–execute cycle. CPU speed is quoted in GHz (clock cycles per second); "dual/quad/octa core" = number of processing units on one chip.

4. The memory hierarchy

Fastest and smallest at the top:

1. Registers (inside CPU)
2. Cache (SRAM — between CPU and RAM; L1/L2/L3)
3. Primary memory:
   • RAM — volatile, read/write. DRAM (main memory, needs refresh) vs SRAM (cache, faster, costlier).
   • ROM — non-volatile, holds firmware/BIOS. Family: PROM (programmable once), EPROM (erase by UV light), EEPROM (erase electrically — flash memory's ancestor).
4. Secondary storage — non-volatile, large: HDD (magnetic), SSD (flash, no moving parts), optical discs (CD ~700 MB, DVD ~4.7 GB, Blu-ray ~25 GB), pen drives.

The volatility question is guaranteed: RAM loses data on power-off (volatile); ROM, HDD, SSD do not. And cache sits between the CPU and main memory — not on the hard disk.

5. Storage units — the ladder

$4\text{ bits}=1\text{ nibble},8\text{ bits}=1\text{ byte}$

$1\text{KB}=1024\text{B}\to 1\text{MB}=1024\text{KB}\to 1\text{GB}=1024\text{MB}\to 1\text{TB}=1024\text{GB}\to \text{PB}\to \text{EB}$

SSC uses the binary convention (1024, not 1000). One character of text ≈ 1 byte.

6. Devices and ports

• MICR — cheques (Magnetic Ink Character Recognition); OMR — exam bubble sheets; OCR — printed text to editable text.
• Printers: impact (dot-matrix) vs non-impact (inkjet, laser); plotters draw large engineering drawings.
• Ports: USB (universal, hot-pluggable), HDMI (audio + video), VGA (older, video only), Ethernet/RJ-45 (network).

7. Software and languages

• System software runs the machine: OS (Windows, Linux, Android), device drivers, utilities.
• Application software serves the user: MS Word, browsers, Tally.
• Compiler translates a whole high-level program to machine code at once (C, C++); an interpreter translates line-by-line (Python, older BASIC).
• Machine language = binary (the only language the CPU executes); assembly uses mnemonics and needs an assembler.

Binary conversion (one method, both directions): decimal → binary by repeated division by 2 reading remainders bottom-up: $25=11001_2$ (check: $16+8+1=25$). Binary → decimal by positional weights $\dots 16,8,4,2,1$.

8. Exam protocol

1. This module is qualifying — target accuracy, not heroics. 15 clean answers beat 20 rushed ones at −1 each.
2. Full forms are free marks: ALU, CU, RAM/ROM, PROM/EPROM/EEPROM, MICR/OMR/OCR, USB, HDMI.
3. For unit conversions, write the 1024 ladder in the margin once and read answers off it.
4. Device-classification questions: ask "does data go into the computer or out?" — plotter out, scanner in, touchscreen both.
5. Revise this fact sheet in the last 48 hours; recall decays fast and the module rewards freshness.