IGCSE Computer Science
30 videosRevision videos for IGCSE Computer Science, unit by unit: Grade 9 data representation, data transmission and hardware.
Grade 9 · Unit 1: Data representation
2:41Denary, binary and hexadecimal
Place values, converting denary to binary and back, and why hex is used for bytes.
2:30Binary addition, overflow and shifts
Adding binary numbers with carries, overflow when a ninth bit is needed, and logical shifts as multiply and divide.
2:12Two's complement
Negative numbers in binary: the -128 place value, invert and add one, and reading a signed byte.
1:45Text: ASCII and Unicode
Character sets give every character a code. ASCII's 128 codes, Unicode's millions, and the storage trade-off.
1:27Images
Pixels, resolution, colour depth, image file size and metadata.
1:38Sound
Sampling an analogue wave: sample rate, bit depth, quality against file size.
1:50Storage units and file sizes
Bit to pebibyte in steps of 1024, and calculating image and sound file sizes.
1:58Compression
Why files are compressed, lossy against lossless, and run-length encoding step by step.
5:38Unit 1 quiz
Ten questions with a think-time countdown and explained answers.
Grade 9 · Unit 2: Data transmission
1:32Data packets and packet switching
Packet structure, routing, out-of-order arrival and reassembly.
1:19Simplex, half-duplex and full-duplex
Which way the data flows, and when.
1:43Serial and parallel transmission
Bits one by one or all at once, skew, crosstalk and USB.
1:21Error detection
Why errors happen, and checksums, echo checks and ARQ.
1:13Parity checks
Parity bits and parity blocks, including finding and fixing a flipped bit.
1:32Check digits
The multiply, add, divide-by-10 method with a worked example and a practice question.
1:28Encryption
Eavesdroppers, symmetric keys and the public and private key pair.
5:08Unit 2 quiz
Ten questions with a think-time countdown and explained answers.
1:32Crosstalk in transmission
How a signal leaks into a neighbouring wire, corrupts data, and how twisted pairs and shielding fix it.
1:48When to use serial or parallel
Choosing between serial and parallel: inside a computer, computer to printer, USB, Ethernet and a distance rule of thumb.
Grade 9 · Unit 3: Hardware
1:21Inside the CPU
The control unit, ALU and registers, the Von Neumann architecture and the three buses.
1:36The fetch-decode-execute cycle
Follow one instruction through the PC, MAR, MDR, CIR and ACC registers, then run a small program.
1:28What makes a CPU faster?
Clock speed, number of cores and cache size, with the run times worked out.
1:00Embedded systems
A computer built into a device for one job: examples, and how it differs from a general-purpose computer.
1:45Input devices
Keyboards, mice, touch screens, microphones, cameras, scanners and barcode / QR readers.
1:41Output devices
Screens, projectors, printers, 3D printers and speakers: what each one does.
1:06Sensors and actuators
A control loop: a sensor measures, the processor decides, an actuator acts. A thermostat shown step by step.
1:29Primary storage: RAM, ROM and virtual memory
Volatile RAM, non-volatile ROM with the boot program, and what virtual memory does when RAM is full.
1:30Secondary storage
Magnetic, optical and solid-state storage, plus cloud storage.
1:34Network hardware: NIC, MAC, IP and routers
What a network interface card, MAC address, IP address (IPv4 and IPv6) and router each do.
5:10Unit 3 quiz
Ten questions with a think-time countdown and explained answers.