Computer Fundamentals & Architecture
DSSSB TGT CS — Section B P1 (Rank 6). Concise MCQ-ready notes.
1. Hardware vs Software
| Hardware | Software |
|---|---|
| Physical components (CPU, RAM, HDD, keyboard) | Programs & data instructions |
| Tangible | Intangible |
| Examples: motherboard, monitor | OS, apps, drivers |
Firmware: software embedded in hardware (ROM) — e.g., BIOS/UEFI.
2. Input / Output Devices
Input: keyboard, mouse, scanner, mic, webcam, joystick, barcode reader, touchscreen (also output)
Output: monitor, printer, speaker, projector
Both (I/O): touchscreen, network NIC, external drive
Trap: Soft copy = screen; hard copy = printout.
3. Memory Hierarchy (fast/small/expensive → slow/large/cheap)
Registers → Cache (L1/L2/L3) → RAM (Main) → Secondary (HDD/SSD) → Offline (tape/optical)| Level | Role |
|---|---|
| Registers | Inside CPU; fastest; very small |
| Cache | Holds frequently used data/instructions |
| RAM | Main memory; volatile; working programs |
| ROM | Non-volatile; boot firmware etc. |
| Secondary | Permanent storage; large capacity |
Volatile: RAM loses data on power off. Non-volatile: ROM, HDD, SSD, flash.
ROM variants (names for MCQs)
- PROM, EPROM, EEPROM, Flash (electrically erasable)
4. Storage Units
| Unit | Size |
|---|---|
| Bit | 0 or 1 |
| Nibble | 4 bits |
| Byte | 8 bits |
| KB | 1024 B (binary) / sometimes 1000 (SI) |
| MB | 1024 KB |
| GB | 1024 MB |
| TB | 1024 GB |
| PB | 1024 TB |
Trap: Exam often uses 1024 (2¹⁰). 1 Byte = 8 bits.
5. Types of Software
| Type | Purpose | Examples |
|---|---|---|
| System | Manage hardware & platform | OS, device drivers, firmware |
| Application | End-user tasks | Word processor, browser, games |
| Utility | Maintenance / support | Antivirus, disk cleanup, backup, zip |
Middleware (extra): software between OS and apps (exam occasional).
6. Language Translators
| Translator | Role |
|---|---|
| Assembler | Assembly → machine code |
| Compiler | HLL entire program → machine/bytecode before run |
| Interpreter | HLL line-by-line / statement execution |
| Linker | Combines object files |
| Loader | Loads program into memory for execution |
| Compiler | Interpreter |
|---|---|
| Whole program translation first | Translates while executing |
| Errors shown after compile phase | Stops at first runtime error often |
| Usually faster execution after compile | Easier debugging / portability feel |
7. Generations of Computers (brief)
| Gen | Era cue | Technology |
|---|---|---|
| 1st | 1940s–50s | Vacuum tubes |
| 2nd | 1950s–60s | Transistors |
| 3rd | 1960s–70s | ICs |
| 4th | 1970s– | Microprocessors |
| 5th | Present concept | AI, ULSI, parallel / intelligent systems |
8. CPU Components
| Part | Function |
|---|---|
| ALU | Arithmetic & logic operations |
| CU | Control Unit — directs operations, fetch/decode |
| Registers | Tiny fast storage (PC, IR, ACC, MAR, MDR…) |
Common registers
- PC (Program Counter): address of next instruction
- IR (Instruction Register): current instruction
- ACC (Accumulator): ALU results
- MAR / MDR: memory address / data registers
Instruction cycle: Fetch → Decode → Execute (→ Store)
9. von Neumann Architecture
- Shared memory for instructions and data
- Sequential execution via program counter
- Components: CPU, memory, I/O, buses
- Bottleneck: single bus/memory path for code & data (von Neumann bottleneck)
- Contrast idea: Harvard — separate instruction & data memories/paths
10. Buses
| Bus | Carries |
|---|---|
| Data bus | Actual data (bidirectional typically) |
| Address bus | Memory/I/O addresses (CPU → memory; width → addressable space) |
| Control bus | Control signals (read/write, interrupt, clock…) |
11. I/O Techniques
| Method | Idea |
|---|---|
| Programmed I/O | CPU waits/polls device continuously |
| Interrupt-driven | Device interrupts CPU when ready |
| DMA | Direct Memory Access — device↔memory transfer with minimal CPU |
Trap: DMA frees CPU from byte-by-byte transfer; DMA controller manages transfer.
12. Secondary Storage
| Type | Notes |
|---|---|
| HDD | Magnetic platters; cheaper/GB; mechanical |
| SSD | Flash memory; faster, shock-resistant, costlier/GB |
| Optical | CD / DVD / Blu-ray |
| Flash drives | USB pen drives, memory cards |
| Magnetic tape | Backup / archive; sequential |
13. Motherboard & Ports
Motherboard: main PCB connecting CPU, RAM slots, chipset, expansion slots, power connectors, ports.
Common ports / interfaces
- USB, HDMI, VGA/DisplayPort, Ethernet (RJ-45), audio jack, Thunderbolt
- Legacy: PS/2, serial, parallel (older MCQs)
- Internal: SATA, PCIe, M.2
14. Cloud Computing Types (brief)
| Model | You manage roughly | Provider gives |
|---|---|---|
| IaaS | OS, apps, data | Virtual machines, storage, network |
| PaaS | Apps & data | Runtime, middleware, OS |
| SaaS | Mostly usage/config | Full application (email, CRM) |
Deployment: public, private, hybrid, community.
15. Firmware: BIOS / UEFI
| BIOS | UEFI |
|---|---|
| Older firmware interface | Modern replacement |
| 16-bit limitations historically | Richer UI, larger disks (GPT), secure boot |
| POST + boot loader handoff | Same role, enhanced features |
- Stored in non-volatile chip on motherboard
- Initializes hardware (POST) and starts boot process
Quick traps checklist
- RAM volatile; ROM/secondary non-volatile.
- Cache sits between registers and RAM in hierarchy.
- 1 Byte = 8 bits; KB often 1024 bytes in exams.
- Compiler = whole program; interpreter = execute while translating.
- ALU computes; CU controls.
- von Neumann: shared memory for code & data.
- Address bus width → max addressable memory.
- DMA = memory↔device without constant CPU babysitting.
- SSD ≠ optical; HDD = magnetic.
- IaaS / PaaS / SaaS = increasing abstraction toward apps.