CDS Physics · Free notes
Electronics and Computers: CDS Physics
Electronics and Computer Fundamentals has 23 past-year questions in CDS General Knowledge, from 2016 (II) to 2026 (II): 10 EASY, 12 MODERATE and 1 HARD. Twenty-one of them come from 2025 and 2026, so this is the newest part of the paper and it is growing. Only one asks about electronics (the transistor); the rest are computer facts on software, languages, memory, networks and security. Most are one-line recall, so learn the terms in the tables exactly, and note the year beside any fact that has changed over time.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Electronics, Hardware and Data
9 PYQsSemiconductors and the transistor, the five computer generations with quantum computing and AI, memory types and file sizes, and binary numbers with logic operators.
Software and Networks
14 PYQsSystem and application software and the jobs of an operating system, machine, assembly, high-level and markup languages, the layers and ports of the internet, and firewalls and malware.
Formula & revision sheet
2 formulas · 6 reference tables · 17 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
2 formulas · 6 reference tables · 17 gotchas across all subtopics — the exam-eve cheat-sheet
Formulas (2)
Reference tables (2)
Semiconductors, diodes and transistors3 rows
| Region of a transistor | Doping | Size |
|---|---|---|
| Emitter | Heavy (the most impurity): it supplies the charge carriers | Medium |
| Base | Light (the least impurity) | Very thin, so carriers cross it without being lostQ CDS 2016 (II): in a bipolar junction transistor the base has the least impurity. |
| Collector | Moderate | The largest, so it can get rid of heat |
Computer generations and new kinds of computing5 rows
| Generation | Main hardware | Roughly when |
|---|---|---|
| First | Vacuum tubes | 1940s to mid 1950s |
| Second | Transistors | Late 1950s to mid 1960s |
| Third | Integrated circuits (ICs) | Mid 1960s to early 1970s |
| Fourth | Microprocessors (very large scale integration) | From 1971Q CDS 2026 (I): the fourth generation used microprocessors. |
| Fifth | Artificial intelligence and parallel processing | Still developing |
Watch out for (9)
- The base is thin and lightly doped→ Semiconductors, diodes and transistors
- A hot semiconductor conducts better→ Semiconductors, diodes and transistors
- Integrated circuits are the third generation, microprocessors the fourth→ Computer generations and new kinds of computing
- A qubit belongs to quantum computers→ Computer generations and new kinds of computing
- Flash is erased electrically, not by ultraviolet light→ Memory, storage and file sizes
- Bits are not bytes→ Memory, storage and file sizes
- Two sizes of megabyte→ Memory, storage and file sizes
- AND needs both, OR needs one→ Binary numbers and logic operators
- Flip, then add 1→ Binary numbers and logic operators
Reference tables (4)
System software, application software and the operating system6 rows
| Software | Kind | What it does |
|---|---|---|
| Windows, Linux, UNIX | System (operating system) | Manages memory, files, devices and the user interface |
| Linker | System | Joins compiled code with the subroutines it callsQ CDS 2026 (II): linking a program with its subroutines is not a job of the operating system. |
| Compiler, interpreter, assembler | System | Turn a program into machine code |
| Spreadsheet, MS PowerPoint, AutoCAD | Application | Do a task for the user |
| UNIX | System (operating system) | Written in C; portable, multi-user and time-sharedQ CDS 2026 (I): UNIX can be time-shared by several users. |
| AUTOEXEC.BAT | Start-up file (MS-DOS) | A list of commands run automatically when the computer startsQ CDS 2026 (II): AUTOEXEC.BAT holds the commands run at start-up. |
Machine, assembly, high-level and markup languages4 rows
| Level | What it looks like | Examples |
|---|---|---|
| Machine language | 0s and 1s run directly by the processor | The processor's own instruction codes |
| Assembly language | Short words (mnemonics), one for each machine code | x86 assembly, MIPS assemblyQ CDS 2026 (I): of Python, Java, x86 and MIPS, the assembly languages are x86 and MIPS. |
| High-level language | Close to English; runs on many processors | Python, Java, C |
| Markup language | Tags that label the parts of a document | SGML, HTML, XMLQ CDS 2026 (II): SGML is an open standard that does not depend on a computer's hardware. |
Networks, protocols and mobile communication4 rows
| TCP/IP layer | What it does | Examples |
|---|---|---|
| Application | The services users' programs call on | HTTP, FTP, SMTP, TELNET, DNS |
| Transport | Delivers data between programs on two machines | TCP, UDP |
| Internet | Gives addresses and routes packets | IP |
| Link | Sends bits over the local connection | Ethernet, Wi-Fi |
Firewalls and malware7 rows
| Term | What it is |
|---|---|
| Firewall | Checks every packet against rules and blocks what is not allowedQ CDS 2025 (II): a firewall examines packets, prevents unauthorised access and blocks suspicious activity. |
| Virus | Malware that attaches to a file and spreads when that file is run |
| Worm | Malware that spreads by itself across a network |
| Trojan horse | Malware that looks like useful software but carries a harmful partQ CDS 2025 (I): the Trojan horse is the malicious software among hacking, password cracking and a firewall. |
| Ransomware | Malware that locks the user's files and demands money |
| Spyware | Malware that secretly records what the user does |
| Phishing | A fake message or website that tricks a user into giving passwords |
Watch out for (8)
- Linking is the linker's job→ System software, application software and the operating system
- AUTOEXEC.BAT runs commands; CONFIG.SYS loads drivers→ System software, application software and the operating system
- Assembly belongs to one processor family→ Machine, assembly, high-level and markup languages
- A markup language does not depend on the machine→ Machine, assembly, high-level and markup languages
- TCP and IP are not application protocols→ Networks, protocols and mobile communication
- Software ports are numbers, not sockets→ Networks, protocols and mobile communication
- A firewall is not antivirus→ Firewalls and malware
- Hacking is not software→ Firewalls and malware
PYQ weightage by concept
8 concepts · 23 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
8 concepts · 23 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Computer generations and new kinds of computing | 3 | 13% |
| Memory, storage and file sizes | 3 | 13% |
| Binary numbers and logic operators | 2 | 9% |
| Semiconductors, diodes and transistors | 1 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| System software, application software and the operating system | 5 | 22% |
| Machine, assembly, high-level and markup languages | 3 | 13% |
| Networks, protocols and mobile communication | 3 | 13% |
| Firewalls and malware | 3 | 13% |
Test yourself on Electronics and Computer Fundamentals
10 past CDS questions from this chapter, timed at 10 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.