Syllabus topics: Computer organization — functional components, input/output devices, storage types, memory hierarchy. Types of computers — micro, mini, mainframe, and supercomputers. Networking fundamentals — definition, need for networks, types (LAN, WAN, MAN), topology (star, ring, bus). Internet basics — IP address, domain name, web browser, email, WWW.
| Input devices | Output devices |
|---|---|
| Keyboard, mouse, trackball | Monitor (LCD, LED, OLED) |
| Scanner, barcode reader, QR reader | Printer (laser, inkjet, dot-matrix) |
| Microphone, webcam | Speakers, headphones |
| Joystick, light pen, graphics tablet | Plotter |
| Touch screen (also output) | Projector |
| OMR, OCR, MICR readers | Braille display |
| Biometric scanners |
OMR (Optical Mark Recognition) reads pencil marks — how your answer sheets are graded. OCR (Optical Character Recognition) reads printed text. MICR (Magnetic Ink Character Recognition) reads the numbers along the bottom of a cheque.
A touch screen is both an input and an output device. So is a network interface card, and a modem. Exams like this question.
▲ faster, smaller, more expensive per byte
│
┌────────────────────┐
│ Registers │ < 1 KB ~1 ns
├────────────────────┤
│ Cache (L1/L2/L3) │ KB–MB ~10 ns
├────────────────────┤
│ Main memory RAM │ GB ~100 ns
├────────────────────┤
│ Secondary: SSD │ GB–TB ~100 µs
├────────────────────┤
│ Secondary: HDD │ TB ~10 ms
├────────────────────┤
│ Tertiary: tape, │ TB–PB seconds
│ optical, cloud │
└────────────────────┘
│
▼ slower, larger, cheaper per byte
The hierarchy exists because of a trade-off. Fast memory is expensive, so you can afford only a little; cheap memory is slow, so you cannot work directly from it. The compromise keeps frequently used data in the fast levels — which works because programs exhibit locality of reference: they tend to reuse the same data and instructions repeatedly.
| Primary | Secondary | |
|---|---|---|
| Also called | Main memory | Auxiliary / backing store |
| Volatile | RAM yes, ROM no | No |
| Speed | Fast | Slow |
| Cost per byte | High | Low |
| CPU access | Direct | Only via primary memory |
| Examples | RAM, ROM, cache | HDD, SSD, DVD, tape |
| RAM | ROM | |
|---|---|---|
| Full name | Random Access Memory | Read Only Memory |
| Volatile | Yes — contents lost on power-off | No |
| Writable | Yes | No (or with difficulty) |
| Holds | Programs and data in current use | Firmware, BIOS, bootstrap |
| Types | SRAM, DRAM | PROM, EPROM, EEPROM, Flash |
SRAM vs DRAM: SRAM uses flip-flops, is fast and expensive, and is used for cache. DRAM uses capacitors that leak charge and must be refreshed thousands of times a second — slower and cheaper, and used for main memory.
ROM variants:
| Unit | Size |
|---|---|
| 1 nibble | 4 bits |
| 1 byte | 8 bits |
| 1 KB | 1024 bytes (2¹⁰) |
| 1 MB | 1024 KB (2²⁰) |
| 1 GB | 1024 MB (2³⁰) |
| 1 TB | 1024 GB (2⁴⁰) |
| 1 PB | 1024 TB (2⁵⁰) |
Storage manufacturers use powers of 10 (1 GB = 1,000,000,000 bytes), which is why a "500 GB" drive shows as about 465 GB in the operating system. The unambiguous binary units are KiB, MiB, GiB.
| Type | Size | Users | Speed | Use | Examples |
|---|---|---|---|---|---|
| Microcomputer | Desk | 1 | Lowest | Personal work | PC, laptop, tablet, phone |
| Minicomputer | Cabinet | 10s–100s | Medium | Departmental | PDP-11, VAX |
| Mainframe | Room | 1000s | High | Banking, airlines, census | IBM z-series |
| Supercomputer | Building | Few, large jobs | Highest | Weather, simulation, research | PARAM, Cray, Fugaku |
India's supercomputers are worth naming: the PARAM series, begun by C-DAC in 1991 under Dr Vijay Bhatkar, and PARAM Siddhi-AI, currently the fastest in the country.
Mainframe vs supercomputer is a standard question. A mainframe handles an enormous number of transactions simultaneously — reliability and throughput matter most. A supercomputer performs an enormous number of calculations on one problem — raw floating-point speed matters most. A bank needs a mainframe; a weather forecast needs a supercomputer.
DEFINITION
A computer network is two or more computers connected to share resources and communicate.
WHY IT MATTERS
Why networks exist:
| Type | Full name | Range | Speed | Ownership | Example |
|---|---|---|---|---|---|
| PAN | Personal Area Network | ~10 m | Low | Individual | Bluetooth earphones |
| LAN | Local Area Network | Building/campus | High | Private | College lab |
| MAN | Metropolitan Area Network | A city (~50 km) | Medium | Private or public | City cable network |
| WAN | Wide Area Network | Country/world | Lower | Usually public | The Internet |
The Internet is the largest WAN. LANs are fast and privately owned; WANs are slower per link and usually rely on leased telecommunications infrastructure.
Topology is the arrangement of the connections.
| Topology | Structure | Advantages | Disadvantages |
|---|---|---|---|
| Bus | All nodes on one backbone cable | Cheap, simple, little cable | One cable break kills the whole network; collisions; hard to fault-find |
| Star | All nodes to a central hub/switch | Easy to add nodes; one node failing does not affect others; simple to diagnose | The hub is a single point of failure; more cable |
| Ring | Each node to the next, forming a loop | No collisions; equal access | One break can stop everything; adding a node disrupts the ring |
| Mesh | Every node to every other | Highly reliable; multiple paths | Very expensive; n(n−1)/2 cables |
| Tree | Hierarchy of star networks | Scalable; easy to extend | Depends on the root; complex cabling |
| Hybrid | Combination | Flexible | Complex and costly |
The syllabus names star, ring and bus specifically. Know all three thoroughly, and be able to draw them.
BUS STAR RING
─┬────┬────┬────┬─ ┌───┐ ┌───┐ ┌───┐
│ │ │ │ ┌──┤ A │ ┌┤ A ├────┤ B ├┐
┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐ │ └───┘ │└───┘ └───┘│
│A│ │B│ │C│ │D│ ┌──┴──┐ ┌───┐ │ │
└─┘ └─┘ └─┘ └─┘ │ HUB ├──┤ B │ │┌───┐ ┌───┐│
└──┬──┘ └───┘ └┤ D ├────┤ C ├┘
│ ┌───┐ └───┘ └───┘
└──┤ C │
└───┘
Star is the dominant topology today — every Ethernet network with a switch is physically a star.
The mesh cable count is a common numerical question: a full mesh of n nodes needs n(n−1)/2 links. For 6 nodes that is 15.
| Device | Function | OSI layer |
|---|---|---|
| Repeater | Amplifies a weakening signal | Physical (1) |
| Hub | Broadcasts to every port — "dumb" | Physical (1) |
| Switch | Forwards only to the correct port using MAC addresses | Data link (2) |
| Bridge | Connects two LAN segments | Data link (2) |
| Router | Routes between different networks using IP addresses | Network (3) |
| Gateway | Connects networks using different protocols | All |
| Modem | Modulates/demodulates for analogue lines | Physical (1) |
Hub vs switch is examined constantly: a hub sends every frame to every port, wasting bandwidth and creating collisions; a switch learns which device is on which port and sends the frame only there.
| Mode | Direction | Example |
|---|---|---|
| Simplex | One way only | Keyboard to computer; television broadcast |
| Half duplex | Both ways, one at a time | Walkie-talkie |
| Full duplex | Both ways simultaneously | Telephone |
A global network of networks using the TCP/IP protocol suite. It began as ARPANET in 1969 (US Department of Defense) and reached India in 1995.
The Internet is not the Web. The Internet is the infrastructure; the World Wide Web is one service running on it, alongside email, FTP and many others. That distinction is a reliable two-mark question.
A unique numeric identifier for a device on a network.
| IPv4 | IPv6 | |
|---|---|---|
| Size | 32 bits | 128 bits |
| Format | Four decimal octets: 192.168.1.1 |
Eight hex groups: 2001:0db8::7334 |
| Total addresses | ~4.3 billion | ~3.4 × 10³⁸ |
| Notation | Dotted decimal | Colon hexadecimal |
IPv6 exists because IPv4 ran out. 4.3 billion addresses seemed limitless in 1981 and are not remotely enough today.
IPv4 classes:
| Class | First octet | Use |
|---|---|---|
| A | 1–126 | Very large networks |
| B | 128–191 | Medium networks |
| C | 192–223 | Small networks |
| D | 224–239 | Multicast |
| E | 240–255 | Experimental |
127.0.0.1 is localhost — the machine itself. Private ranges
(10.x.x.x, 172.16–31.x.x, 192.168.x.x) are not routable on the public
Internet, which is why your home router hands out 192.168.1.x.
Humans remember google.com; machines need 142.250.183.14. The Domain Name
System translates between them — effectively the Internet's phone book.
www . example . com
│ │ │
│ │ └─ Top-level domain (TLD)
│ └──────────── Second-level domain
└───────────────────── Subdomain / host
Top-level domains: .com (commercial), .org (organisation), .edu
(education), .gov (government), .net (network), plus country codes such as
.in, .uk, .us. India also has .ac.in for academic institutions and
.gov.in for government.
https://www.example.com:443/folder/page.html?id=42#section
│ │ │ │ │ │
protocol domain port path query fragment
Invented by Tim Berners-Lee at CERN in 1989. Its three foundations:
HTTP vs HTTPS: HTTPS adds TLS encryption. Anything involving a password or payment must use HTTPS; the padlock in the address bar indicates it.
Software that requests, interprets and displays web pages: Chrome, Firefox, Safari, Edge. Its core components are the rendering engine (which draws HTML and CSS), the JavaScript engine, and the network layer.
| Protocol | Purpose | Port |
|---|---|---|
| SMTP | Sending mail | 25, 587 |
| POP3 | Downloading mail (usually deleting from the server) | 110, 995 |
| IMAP | Reading mail while leaving it on the server | 143, 993 |
POP3 vs IMAP: POP3 downloads and typically deletes, so mail lives on one device. IMAP synchronises, so the same mailbox appears identically on your phone and laptop. IMAP is what almost everyone uses now.
Email address structure: username@domain.com — the local part, @, and
the domain.
Cc vs Bcc: every recipient sees the Cc list; nobody sees the Bcc list. Using Cc where Bcc was needed exposes everyone's address to everyone else — a real privacy failure, and a good exam point.
| Protocol | Purpose |
|---|---|
| TCP | Reliable, connection-oriented delivery |
| UDP | Fast, connectionless, no delivery guarantee |
| IP | Addressing and routing |
| HTTP/HTTPS | Web pages |
| FTP | File transfer |
| SMTP/POP3/IMAP | |
| DNS | Name resolution |
| DHCP | Automatic IP address assignment |
TCP vs UDP: TCP guarantees delivery and order, at the cost of speed — used for web pages, email and file transfer. UDP does neither, and is used where speed matters more than perfection: live video, voice calls, online games. A dropped frame in a video call is better than a stalled one.
Windows is not the only operating system a candidate is asked about. Two others appear in recruitment syllabuses, and both are asked at the level of what it is and what the common commands do — not at the level of administering one.
Linux is open source: the source code is published, anyone may read, modify and redistribute it, and there is no licence fee. That single fact explains most of its advantages:
| Feature | What it means in practice |
|---|---|
| Open source | No licence cost; the code can be audited and modified |
| Multi-user | Several users work on one machine at once, each with their own permissions |
| Multi-tasking | Many processes run concurrently |
| Portable | Runs on everything from a phone to a supercomputer |
| Stable and secure | Long uptimes; permissions and user separation are built in, not added |
| Shell | A command interpreter — bash is the usual one — that scripts anything you can type |
DEFINITION
A distribution is the kernel plus the tools packaged together — Ubuntu, Fedora, Debian, Red Hat. The kernel is the same idea in each; what differs is the packaging, the release policy and the default software.
| Command | What it does |
|---|---|
cat file |
Display a file's contents |
cp source dest |
Copy |
mv source dest |
Move, and also rename — there is no separate rename command |
rm file |
Delete a file |
touch file |
Create an empty file, or update its timestamp |
head -n 5 file |
First 5 lines |
tail -n 5 file |
Last 5 lines |
wc -l file |
Count lines |
grep pattern file |
Print the lines that match a pattern |
| Command | What it does |
|---|---|
pwd |
Print the working directory — where you are now |
ls |
List the contents; ls -l adds permissions, owner, size and date |
cd dir |
Change directory; cd .. goes up one, cd ~ goes to your home directory |
mkdir dir |
Create a directory |
rmdir dir |
Remove an empty directory |
rm -r dir |
Remove a directory and everything inside it |
Paths are worth stating explicitly, because the distinction is examined: an
absolute path starts from the root and begins with /, as in
/home/ravi/notes.txt. A relative path starts from wherever you are, as in
notes.txt or ../data/notes.txt.
| Command | What it does |
|---|---|
whoami |
The current user |
useradd name |
Create a user account |
passwd name |
Set or change a password |
usermod |
Modify an existing account |
userdel name |
Delete an account |
groupadd name |
Create a group |
su name |
Switch user |
sudo command |
Run one command with superuser privileges |
The root user has unrestricted rights. Ordinary work is not done as root;
sudo is used to borrow those rights for a single command, so that a mistake
affects one command rather than the whole session.
Every file carries three permissions for each of three classes of user:
| Permission | Value | On a file | On a directory |
|---|---|---|---|
| r read | 4 | Read the contents | List the contents |
| w write | 2 | Modify the contents | Create or delete files inside |
| x execute | 1 | Run it as a program | Enter it with cd |
The three classes are the owner, the group, and others. ls -l
shows them as nine characters, for example -rwxr-xr--: the first character is
the file type, then rwx for the owner, r-x for the group, r-- for others.
chmod changes them, and the numeric form is the one asked for. Add the values
for each class and write the three digits in order:
rwx = 4 + 2 + 1 = 7r-x = 4 + 0 + 1 = 5r-- = 4 + 0 + 0 = 4so chmod 754 file produces exactly -rwxr-xr--. Two more that are worth
knowing on sight: 644 is rw-r--r--, the normal permission for a document,
and 755 is rwxr-xr-x, the normal permission for a program or a directory.
chown user file changes the owner; chgrp group file changes the group.
macOS is Apple's operating system for Macintosh computers. It is built on a
Unix foundation, which is why its Terminal accepts most of the commands
above unchanged — ls, cd, pwd, cp, mv, chmod all behave as they do
on Linux.
What it adds is the graphical layer: Finder for files, the Dock for launching applications, Spotlight for search, Mission Control for managing windows and desktops, and Time Machine for backups. Its advantages as usually listed are a consistent interface, tight integration with Apple hardware, strong multimedia support and Unix stability underneath.
The examinable contrast in one line: Windows uses \ as its path separator
and drive letters such as C:; Linux and macOS use / and a single tree
starting at root, with no drive letters at all.
Two marks
Five marks
Ten marks
Explain computer organization — functional components, I/O devices, storage types and the memory hierarchy.
Explain networking fundamentals — the need for networks, types, topologies and devices — with diagrams.
COMMON ERRORS