Memory, Number Systems and Operating Systems
Memory, Number Systems and Operating Systems
Memory questions ask the units of storage and the difference between RAM, ROM, cache and secondary storage. Number system questions ask quick binary, octal and hexadecimal conversions. Operating system questions ask what an OS does and name examples. All three appear in recent NTPC papers.
1. Memory Units and Types
| Unit | Size |
|---|---|
| Bit | 0 or 1 |
| Nibble | 4 bits |
| Byte | 8 bits |
| Kilobyte (KB) | 1,024 bytes |
| Megabyte (MB) | 1,024 KB |
| Gigabyte (GB) | 1,024 MB |
| Terabyte (TB) | 1,024 GB |
| Petabyte (PB) | 1,024 TB |
| Memory | Key facts |
|---|---|
| RAM | Primary, volatile, read-write; called random access because any location can be reached directly in the same time |
| ROM | Primary, non-volatile; holds start-up instructions; PROM, EPROM, EEPROM types |
| Cache | Very fast memory between CPU and RAM; holds frequently used data |
| Registers | Fastest memory, inside the CPU |
| Secondary storage | Non-volatile: hard disk, SSD, pen drive, CD (about 700 MB), DVD (about 4.7 GB), Blu-ray |
| Speed order | Registers > cache > RAM > secondary storage |
2. Number Systems
| System | Base | Digits |
|---|---|---|
| Binary | 2 | 0, 1 |
| Octal | 8 | 0 to 7 |
| Decimal | 10 | 0 to 9 |
| Hexadecimal | 16 | 0 to 9 and A to F (A = 10, F = 15) |
Decimal to binary: divide by 2 repeatedly and read remainders from bottom to top
Binary to decimal: add place values 1, 2, 4, 8, 16, ... where the bit is 1
One hex digit = 4 bits; one octal digit = 3 bits
3. Operating System and Software
| Item | Fact |
|---|---|
| Operating system | Manages hardware, memory, processes, files and devices; interface between user and hardware |
| Examples | Windows, Linux, macOS, Unix, Android, iOS |
| Booting | Starting the computer and loading the OS; cold boot (power on) and warm boot (restart) |
| Kernel | Core of the OS |
| GUI vs CLI | Windows uses icons (GUI); MS-DOS uses typed commands (CLI) |
| System software | OS, device drivers, utilities |
| Application software | MS Word, browsers, games |
| Compiler | Translates the whole program at once |
| Interpreter | Translates line by line |
| Open-source OS | Linux, Android |
✗ RAM keeps data when power is switched off | ✓ RAM is volatile; ROM and secondary storage keep data without power
✗ 1 KB = 1,000 bytes in computer memory | ✓ In binary measure 1 KB = 1,024 bytes
हिंदी नोट: 1 बाइट = 8 बिट और 1 KB = 1024 बाइट। RAM अस्थायी (वोलेटाइल) और ROM स्थायी स्मृति है। कैश मेमोरी CPU और RAM के बीच तेज़ स्मृति है। ऑपरेटिंग सिस्टम हार्डवेयर, मेमोरी और फ़ाइलों का प्रबंधन करता है; उदाहरण विंडोज़, लिनक्स और एंड्रॉइड।
Exam Pointer: Verified NTPC patterns: bytes in a kilobyte (December 2020 CBT-1), why RAM is called random access (March 2026 Graduate CBT-1) and the main function of an operating system (June 2025 Graduate CBT-1). Number conversions are tagged syllabus-based.
Pariksha Pattern: Every Way NTPC Asks This Topic
Pattern 1: Memory units
[PYQ: NTPC CBT-1 30-Dec-2020 Shift-1]
EXAM LEVEL
Q. How many bits make one byte?
8 bits.
Answer: 8
EXAMATLAS LEVEL
Q. How many kilobytes are in 2 MB, and how many bits are in one nibble? Arrange in increasing size: GB, KB, TB, MB.
2 MB = 2 × 1,024 = 2,048 KB. A nibble has 4 bits. Increasing order: KB, MB, GB, TB.
Answer: 2,048 KB; 4; KB, MB, GB, TB
Pattern 2: RAM, ROM, cache and storage
[PYQ: NTPC Graduate CBT-1 25-Mar-2026 Shift-3]
EXAM LEVEL
Q. Which memory loses its contents when the power is switched off?
RAM, because it is volatile.
Answer: RAM
EXAMATLAS LEVEL
Q. Arrange in decreasing speed: hard disk, registers, RAM, cache. Which memory keeps start-up instructions permanently?
Registers are fastest, then cache, then RAM, then hard disk. ROM keeps the start-up instructions permanently.
Answer: Registers, cache, RAM, hard disk; ROM
Pattern 3: Number system conversion
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. Convert the decimal number 25 into binary.
25 = 16 + 8 + 1, so the bits for 16, 8 and 1 are on: 11001.
Answer: 11001
EXAMATLAS LEVEL
Q. Convert binary 101101 to decimal, and hexadecimal 2F to decimal.
101101 = 32 + 8 + 4 + 1 = 45. 2F = 2 × 16 + 15 = 47.
Answer: 45; 47
Pattern 4: Operating system functions and software types
[PYQ: NTPC Graduate CBT-1 5-Jun-2025 Shift-2]
EXAM LEVEL
Q. Is MS Word system software or application software?
Application software; it helps the user do a task, while system software runs the computer.
Answer: Application software
EXAMATLAS LEVEL
Q. List three jobs of an operating system, name two open-source operating systems, and state how a compiler differs from an interpreter.
An OS manages memory, runs and schedules processes, and organises files and devices. Linux and Android are open source. A compiler translates the whole program at once; an interpreter translates and runs it line by line.
Answer: Memory, process and file management; Linux, Android; whole program vs line by line
60-Second Revision
- 8 bits = 1 byte; 1,024 bytes = 1 KB; nibble = 4 bits.
- RAM volatile, ROM non-volatile, cache between CPU and RAM, registers fastest.
- 25 = 11001; 101101 = 45; hex 2F = 47.
- OS manages hardware, memory, processes and files; Windows, Linux, Android.