Computer Applications for the APFC Exam 2026: Notes, PYQs & MCQs
- Computer applications is a technical block of 5–11 questions a paper — real computer science, not general-science current affairs.
- The MAR holds the address, MBR the data, IR the instruction, PC the next instruction.
- Octal → binary uses 3 bits per digit; hex → binary uses 4 bits; full-mesh links = n(n−1)/2.
- Each IP octet is 0–255; a real-time OS responds within a strict deadline; Java is object-oriented (not top-down).
- The modern layer — SSL/TLS, cloud computing, AI/ML and GPUs — is growing in the recent papers.
Computer applications is a technical, high-yield block in the EPFO Assistant Provident Fund Commissioner (APFC) exam — five to eleven questions a paper, and unlike the general-science current affairs a UPSC aspirant knows, this is proper computer science. This guide covers number systems, hardware and the CPU, operating systems, networking, and a thin modern layer of web, cyber-security and AI — with solved previous-year questions and 40 practice MCQs.
Why computer applications is a technical, high-yield topic in the APFC exam
Number-system conversions, CPU registers, the mesh-link formula, IP-address validity and operating-system types recur every sitting; the 2025 paper added a modern layer of AI, GPUs and SSL. Each recurring type is worked below.
Computer hardware and the CPU
- The CPU has the ALU (arithmetic & logic), the Control Unit and registers.
- Registers: the MAR holds the address to be accessed, the MBR/MDR the data, the IR the current instruction, and the Program Counter the address of the next instruction.
- Memory hierarchy: registers → cache → RAM (volatile) → secondary storage; ROM is non-volatile firmware; virtual memory uses disk to extend RAM.
- Peripherals and power: SMPS = Switch Mode Power Supply; USB = Universal Serial Bus; plug-and-play devices work on connection.
- Units: bit < byte (8 bits) < KB < MB < GB < TB < PB, each step 1,024.
Number systems and conversions
The four bases are binary (2), octal (8), decimal (10) and hexadecimal (16). For octal → binary, each digit becomes 3 bits (473 = 100 111 011); for hex → binary, each digit becomes 4 bits; for hex → decimal, multiply each digit by its place value.
The decimal equivalent of the hexadecimal number 5A6D is?
5×16³ + A(10)×16² + 6×16 + D(13) = 20,480 + 2,560 + 96 + 13.
Answer — 23,149
Operating systems and software
- System vs application software: the OS (Windows, Linux, Unix) is system software; Word, Excel and a browser are applications.
- OS types: batch, multiuser, distributed, real-time (strict deadlines) and embedded. Functions: process, memory, file and device management.
- Translators: a compiler converts the whole program at once; an interpreter line by line; an assembler converts assembly to machine code.
- Utilities: disk-error checking (CHKDSK), defragmentation, antivirus.
Which type of operating system is designed to respond to an event within a predetermined time?
A real-time OS is built to meet strict timing deadlines. Note: the 2023 answer key marked “embedded” for this item — know both and read the option set carefully.
Answer — Real-time OS (paper keyed “embedded”)
Networking and the internet
- LAN / WAN / MAN = Local / Wide / Metropolitan Area Network.
- Topologies: bus, star, ring, mesh. A full mesh of n nodes has n(n−1)/2 links.
- Transmission modes: simplex (one way), half-duplex (both ways, one at a time), full-duplex (both ways at once).
- IP addressing: four octets, each 0–255 — so an octet above 255 (e.g. 102.45.221.710) is invalid.
- Devices & protocols: a router connects different networks; FTP, HTTP/HTTPS (secure via SSL/TLS) and SMTP are protocols; spam is unsolicited bulk mail; phishing is deceptive identity theft.
In a mesh topology with six computers, how many links must there be?
Full-mesh links = n(n−1)/2 = 6 × 5 / 2.
Answer — 15
Web, programming and the modern layer
- HTML structures web pages through tags, attributes and hyperlinks.
- Language paradigms: C, FORTRAN and Pascal are procedural / top-down; Java is object-oriented.
- Operators: the dot operator connects a structure variable and its member.
- Cyber-security: SSL/TLS gives secure encrypted communication; malware is countered by firewalls and antivirus.
- Cloud computing delivers software/infrastructure/platform on demand (SaaS, PaaS, IaaS); the modern layer adds AI/ML and GPUs.
Which of the following is not a top-down (procedural) language?
C, FORTRAN and Pascal are procedural/top-down; Java is object-oriented, built around objects and classes.
Answer — Java
Quick-reference: computer applications for the APFC exam
| Item | Key fact |
|---|---|
| CPU registers | MAR = address, MBR = data, IR = instruction, PC = next instruction |
| Storage ladder | bit < byte (8 bits) < KB < MB < GB < TB < PB |
| Octal → binary / Hex → binary | 3 bits per octal digit / 4 bits per hex digit |
| Mesh links / IP octet range | n(n−1)/2 / 0–255 |
| Duplex modes | simplex / half-duplex / full-duplex |
| Translators | compiler (whole) / interpreter (line by line) / assembler (assembly → machine) |
| HTTPS security | SSL/TLS |
Practice MCQs on computer applications for the APFC exam
Forty practice questions covering hardware, number systems, operating systems, networking and the modern layer. Answers follow the set.
1-b 2-b 3-c 4-b 5-b 6-c 7-b 8-a 9-b 10-a 11-d 12-b 13-a 14-a 15-c 16-b 17-b 18-a 19-b 20-c
21-b 22-c 23-b 24-c 25-c 26-c 27-b 28-c 29-b 30-c 31-b 32-d 33-b 34-b 35-b 36-c 37-b 38-b 39-b 40-b
Frequently asked questions
What is the binary equivalent of octal 473?
The binary equivalent of octal 473 is 100111011. Each octal digit converts to three binary bits: 4 = 100, 7 = 111, 3 = 011.
What is the decimal equivalent of hexadecimal 5A6D?
The decimal equivalent of hexadecimal 5A6D is 23,149, calculated as 5×16^3 + 10×16^2 + 6×16 + 13.
How many links are needed in a full mesh topology?
In a full mesh topology of n nodes, the number of links is n(n-1)/2. For six computers, that is 6×5/2 = 15 links.
Which register holds the address of the memory location to be accessed?
The Memory Address Register (MAR) holds the address of the memory location to be accessed. The MBR holds the data, the IR the instruction, and the Program Counter the address of the next instruction.
How do you identify an invalid IP address?
Each octet of an IPv4 address must be between 0 and 255, so any address with an octet above 255, such as 102.45.221.710, is invalid.
What is the difference between simplex, half-duplex and full-duplex?
Simplex transmits in one direction only; half-duplex transmits in both directions but one at a time; full-duplex transmits in both directions simultaneously.
Which is not a top-down (procedural) programming language?
Java is not a top-down (procedural) language; it is object-oriented. C, FORTRAN and Pascal are procedural or top-down languages.
What is a real-time operating system?
A real-time operating system is designed to respond to an event within a strict, predetermined deadline. Examples include control systems for industrial and embedded applications.
