Overview of computer systems
A computer system is hardware plus software working together.
- Input devices: keyboard, mouse, scanner, microphone.
- CPU (central processing unit): follows instructions and calculates.
- Memory (RAM): fast, temporary, forgets when power is off.
- Storage: disk or SSD, keeps files for a long time.
- Output devices: screen, printer, speaker.
Software is the set of programs. System software (operating system) runs the machine. Application software (word processor, accounting program) does your work.
Network mechanisms and configuration
A network joins devices so they can share data and devices.
- LAN: a network in one place (a school, an office). WAN: links places far apart; the internet is the biggest WAN.
- Hub/switch joins devices in a LAN. A router joins networks and chooses the path for packets.
- Client asks for a service; server gives it (files, web pages, mail).
- Each device has an IP address, like a house number, so packets know where to go.
- A message is cut into small packets. Each packet is numbered, travels on its own path and is put back together at the end.
- Rules for talking are called protocols (for example TCP/IP, HTTP).
- Common layouts (topologies): bus, star, ring. Most offices use a star around a switch.
Using information networks
Networks save money and time for businesses and schools:
- Share files, printers and software.
- Email, chat and video calls.
- Websites and online shops; cloud storage and cloud software.
- Central databases for stock, billing and pay.
- Remote work and online classes.
Bandwidth matters: download time = file size in megabits / speed in Mbps. Remember 1 byte = 8 bits.
Ensuring information security and law
Threats: viruses and other malware, phishing (fake messages that steal passwords), hacking, data theft, accidents such as lost devices.
Protections:
- Strong, secret passwords and two-step login.
- Firewall to filter traffic; antivirus; regular software updates.
- Backups kept in another place.
- Access rights: each person sees only what they need.
- Encryption: scrambling data so thieves cannot read it.
Law: countries have laws on data protection, hacking, copyright and electronic records. Breaking them can bring fines or prison. Companies also write their own security rules and train staff.
Try it: trace a packet
Pick a website. Imagine your message cut into 6 packets. Draw your phone, the router, and the server. Mark the packets travelling. Then switch the firewall in the 3D and watch what changes.
Key formulas and definitions
- Computer = hardware (input, CPU, memory, storage, output) + software
- Packets = message size / packet size
- Download time (s) = file size (MB) x 8 / speed (Mbps)
- Security = firewall + password + update + backup
Worked examples
1. List the path of data when you type a letter and see it on the screen.
Keyboard (input) -> CPU (process) -> memory (held for use) -> screen (output). A save copies it to storage.
2. A 3,000-byte message is sent in packets of 500 bytes. How many packets?
3,000 / 500 = 6 packets.
3. A 50 MB file downloads at 10 Mbps. How long does it take?
50 MB x 8 = 400 megabits. 400 / 10 = 40 seconds.
4. Which device joins your home network to the internet?
The router. It also gives local devices their addresses and chooses the next hop for packets.
5. An email says "Your bank account is blocked, click here and enter your password." What is it and what should you do?
It is phishing. Do not click. Report it and contact the bank through its official number.
Common mistakes
- Mixing up memory and storage. RAM is temporary; disk keeps files.
- Thinking the internet and the web are the same. The web is one service that runs on the internet.
- Reading Mbps (megabits) as MBps (megabytes) when finding download time.
- Believing antivirus alone is enough. Passwords, updates and backups also matter.