Lesson 1: How Computers Work
Chapter 1 study guide: quick notes, multiple-choice check, and short written answers.
1. Quick notes
Annotate and print
Use the tool bar at the bottom of the screen to highlight text, draw, and add sticky notes or text on top of these notes. Then save a PDF with or without your marks.
In the print window, choose "Save as PDF" as the destination. Chrome or Edge gives the best result.
The brain analogy
- Input: eyes, ears, nose, skin take in information.
- Processing: the brain compares what it senses with memory to find a match.
- Output: the mouth and muscles give the answer or move.
- A computer works the same way: input device, then CPU + memory, then output device.
CPU (Central Processing Unit)
- The "brain": does all processing, calculation and decisions.
- Does not store data, so storage is needed.
- Very fast: about 4 billion calculations per second.
Why two kinds of storage?
- CPU is very fast, so storage must be fast too, or the CPU is wasted.
- Faster storage costs more, so the storage is split in two.
RAM vs Hard Disk
| RAM | Hard Disk | |
|---|---|---|
| Speed | Fast | Slow |
| Cost | High | Low |
| Size | Small (8 / 16 GB) | Large (512 GB / 1 TB) |
| Holds | Programs and files currently in use | All games, movies, photos, music, programs |
- Example: 16 GB RAM costs about the same as a 1000 GB hard disk (about 60 times more space).
- Opening a game, program or file loads it from Hard Disk to RAM. That is the loading screen.
- Every extra open app takes RAM space.
- When RAM is full, the CPU works with the Hard Disk and the computer slows down badly.
Input and Output devices
- Input: bring data in (keyboard, mouse, microphone).
- Output: send data out (monitor, printer, speakers).
- Some devices do both, for example a touchscreen.
Hardware vs Software
- Hardware: the physical parts (CPU, RAM, Hard Disk, input/output devices).
- Software / program: a set of instructions that tells the hardware what to do.
- Analogy: a manual washing machine needs you to do every step; a modern one has built-in "washing programs".
- Application software: does a specific task for the user (Word, Photoshop, Firefox).
- System software: runs the hardware and gives applications a platform (operating system).
- Programming language: software used to create applications.
- Programming / coding: writing the instructions that make a program.
Binary
- Wires have two states: electricity (1) or no electricity (0).
- Binary is a base-2 system using only 0 and 1. It is the basis of all digital data.
- Each English letter uses 8 bits (1 byte).
- Examples: A =
01000001, B =01000010, N =01001110, O =01001111. - Humans count in base 10 (digits 0 to 9, ten fingers); computers count in base 2.
Possibilities with n bits = 2n
| Bits | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Values | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 256 | 512 | 1024 | 2048 | 4096 |
Memorise: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024. In base 10, 3 digits give 1000 possibilities (000 to 999).
Storage units
- 1 bit = a single 0 or 1. 8 bits = 1 byte.
- 1 KB = 1024 bytes (about 1 thousand)
- 1 MB = 1024 KB (about 1 million bytes)
- 1 GB = 1024 MB (about 1 billion bytes)
- 1 TB = 1024 GB (about 1 trillion bytes)
- Phone with 6 GB RAM + 128 GB storage: RAM sets how many apps run at once; storage sets how many files, photos and videos you can keep.
- Bigger console storage means more games installed at the same time.
CPU speed
- Measured in Hertz (Hz): 1 Hz = 1 operation per second.
- MHz = 1 million Hz; GHz = 1 billion Hz.
- Typical CPU: about 2 GHz = 2 billion operations per second.
Data transfer speed
- Measured in bits per second (bps). Small b = bit, capital B = Byte.
- 1990s: 10 Mbps. 2000s: 100 Mbps. Today: up to 10 Gbps.
- Dial-up was 56 kbps; 1 Gbps is roughly 18,000 times faster.
2. Multiple-choice check
Pick an answer to see right or wrong straight away, with a short explanation.
3. Short written questions
Try to answer in your own words first, then open the model answer.