Computer Basics - Quick Revision

Computer: electronic device that accepts data → processes → gives output → stores result.
CPU = ALU (calculations) + CU (control signals) + MU (memory).
1 Byte = 8 bits; 1 KB = 1024 B; 1 MB = 1024 KB.
Primary memory: RAM (volatile), ROM (non-volatile); Secondary: HDD, SSD, DVD.
Cache (L1/L2/L3) bridges speed gap between CPU & RAM.
OS is system software that manages hardware & provides user interface.
GUI uses icons/windows; CLI uses typed commands.
Machine language: 0-1 only; Assembly: mnemonic codes; High-level: Python, Java.
Compiler: whole program → object code; Interpreter: line-by-line execution.
USB 3.0 speed ≈ 5 Gbps; USB-C is reversible connector.
ASCII 7-bit (128 chars); UTF-8 variable-length, supports all languages.
IP address: 32-bit (IPv4), 128-bit (IPv6); MAC address 48-bit physical address.
HTTP port 80; HTTPS port 443; SMTP port 25.
Virus needs host file; Worm self-replicates; Trojan hides in useful software.
Cloud = on-demand network access to shared computing resources.
Shortcut keys: Ctrl+S (save), Ctrl+C (copy), Ctrl+Z (undo), Ctrl+Shift+Esc (Task Manager).

Formula/Rule	Application
Storage capacity = tracks × sectors × 512 bytes	Find disk size
Data transfer time = file size ÷ transfer speed	Download/upload time
Number of addresses = 2ⁿ (n = address lines)	Memory addressing range
Baud rate = bits per second ÷ bits per symbol	Serial communication speed
Throughput = (useful data) ÷ (total time)	Efficiency of system
Resolution = horizontal × vertical pixels	Screen/image clarity
Color depth bits = log₂(number of colors)	Bits needed per pixel
Sampling rate ≥ 2 × max frequency (Nyquist)	Audio/video digitization
Compression ratio = uncompressed ÷ compressed size	Space saved

“I Prefer My Apples Red” → Input, Process, Memory, Arithmetic, Output, Register.
“RAM Forgets, ROM Remembers” → RAM volatile, ROM permanent.
“GUI = Graphical User Interface” → think “GOOEY” pictures.
OSI layers: “Please Do Not Throw Sausage Pizza Away” → Physical, Data-link, Network, Transport, Session, Presentation, Application.
Port numbers: “80 = HTTP ATE-ZERO security; 443 = HTTPS FOUR-for-THREE encryption”.

Mistake	Correct Approach
Confusing MB (10⁶) with MiB (2²⁰)	Use 1024 for binary units (KiB, MiB)
Saying “ROM is a secondary memory”	ROM is primary & non-volatile
Treating cache as secondary storage	Cache is CPU-level, very fast, small
Writing 1 KB = 1000 B in technical exams	Always write 1024 B unless SI prefix specified
Forgetting USB is both serial & hot-pluggable	Mention these two features explicitly

Glance at shortcut keys & port numbers right before entering hall—easy 1-markers.
For binary/decimal conversions, verify with 2ⁿ table; silly slips cost marks.
If “which is fastest memory?” appears, answer Register (inside CPU), not cache.
In OS questions, always pick multitasking & GUI as key features of modern OS.
Use elimination in confusing options—remove any choice saying “1 KB = 1000 B”.

1. Which of the following is the smallest unit of memory?

A. Byte B. Bit C. Nibble D. Word **Answer:** B. Bit

2. The ALU performs ——— operations.

A. Input B. Arithmetic & Logic C. Storage D. Control **Answer:** B. Arithmetic & Logic

3. Which port is used by HTTPS by default?

A. 80 B. 21 C. 443 D. 25 **Answer:** C. 443

4. Cache memory improves performance due to ———.

A. Higher RPM B. Faster data access to CPU C. Larger capacity D. Magnetic storage **Answer:** B. Faster data access to CPU

5. UTF-8 is a type of ———.

A. Operating System B. Character encoding C. Network protocol D. Compiler **Answer:** B. Character encoding