How computers work

Encryption and hashing

1. 04Two ways to encryptLock and unlock with the same key, or use a matched pair. How the keys get handed out, how many you need, why both get combined, and the calculation you cannot run backwards.11 slides · 13 exercisesGo to the exercises

Proving who you are, and certificates

1. 05Proving you are who you sayA different job from hiding the contents. Who wrote it, whether it was altered on the way, and whether that key is genuine. A tour of the tools for checking.12 slides · 13 exercisesGo to the exercises

How attacks work and get stopped

1. 06How attacks work and get stoppedWhere the holes in your own code are. The classic attack methods, the kinds of malware, and where each gets stopped.12 slides · 13 exercisesGo to the exercises

Table design and normalisation

1. 07Splitting tables the right wayWhy tables come apart, and why JOIN can put them back together. How keys get chosen, and normalisation as the procedure for splitting.12 slides · 13 exercisesGo to the exercises

Transactions and indexes

1. 08Failing halfway without breaking anythingA transfer where only one half happened would be trouble. How things succeed together or get undone together, how they are protected when touched at once, and how they are put back after a crash.12 slides · 13 exercisesGo to the exercises

Data structures

1. 09Ways of laying data outWhat is different between an array you have been pushing to and a list. Straight there by index, or walked to. The shapes data comes in: stack, queue, tree and hash table.12 slides · 13 exercisesGo to the exercises

Searching, sorting and how much work it takes

1. 10Ways of searching and sortingTwo ways of writing the same answer can differ by orders of magnitude once the data grows. The shapes of searching and sorting, the order notation for how effort grows, and recursion.11 slides · 13 exercisesGo to the exercises

Processes and scheduling

1. 11Sharing out a single CPUWhile you sit at node main.js, the browser and the music carry on. There is only one CPU, so why do they look simultaneous? How the order gets decided, interrupts, and keeping two things off the same thing at once.12 slides · 13 exercisesGo to the exercises

Managing memory, and files

1. 12Papering over not having enough memoryWhy a program larger than memory runs at all. Virtual memory and paging, choosing which page to evict, and where files live plus how they are backed up.12 slides · 13 exercisesGo to the exercises

Configuration and redundancy

1. 13Building so a breakage does not stop youWays of splitting the work across several machines, and what you keep ready so one failing machine does not stop everything. Duplication, RAID and the cloud.12 slides · 13 exercisesGo to the exercises

Uptime and performance

1. 14Counting how little it stops and how fast it isHow much does that system stay up, and how fast is it? The handful of formulas and ways of counting that let you say it with numbers rather than impressions.12 slides · 13 exercisesGo to the exercises

Binary and hexadecimal

1. 15Binary and hexadecimalA machine has nothing but 0 and 1. From there, follow the trail to the #ff0000 of colours and to why 0.1 + 0.2 will not come out evenly.12 slides · 13 exercisesGo to the exercises

Logic operations and character codes

1. 16Bit logic and character codesThe four operations that compare bits one place at a time. Masks that pull out just the places you want, shifts that move places along, and the machinery for finding a single broken bit.12 slides · 13 exercisesGo to the exercises

The CPU and running instructions

1. 17The order in which a CPU runs instructionsA computer is made of five units. At the centre of them, how an instruction is fetched, decoded and executed. Plus the formulas for counting speed and the trick of turning it into a production line.11 slides · 13 exercisesGo to the exercises

Layers of storage, and the cache

1. 18Fast memory and slow memoryFast memory is small and expensive. Large memory is slow. Stacking storage in layers because you want both, and the arithmetic of measuring the effect with a hit rate.12 slides · 13 exercisesGo to the exercises

Screen design, images and sound

1. 19The basics of screens and imagesWhy photographs are JPEG and icons are PNG. Who alt is written for. How to build a screen and how to hold the material you put on it.12 slides · 13 exercisesGo to the exercises

The development process, and design

1. 20Arranging the work when several of you build itEverything you did not need while building alone. The names for the order of the work, waterfall and agile, how to split into parts, and object orientation.12 slides · 13 exercisesGo to the exercises

Testing and estimates

1. 21How far to test, and how to estimateIt ran, so we are done - no. How far do you have to try before the doubt clears? Dividing the phases, and choosing the test data.12 slides · 13 exercisesGo to the exercises