Computing o level notes

Preface Underlined words have definitions in Appendix A: Definitions Bolded words r just cos i wanna emphasise 1

1 Computer Architecture In a computer, data is stored as bits . 8 bits = 1 byte, 4 bits = 1 nibble 1 Kilobyte (kB) = 10 3 bytes, Kibibyte (KiB) = 2 10 bytes Megabyte (MB) = 10 6 bytes, Mebibyte (MiB) = 2 20 bytes So on and so forth. You need to memorise until Exabyte / Exibyte Kilo → Mega → Giga → Tera → Peta → Exa Kibi → Mebi → Gibi → Tebi → Pebi → Exi Parts of a computer: Processor It executes instructions. The frequency (Hz) is how many instructions it can carry out in 1 second. Multi-core processors have > 1 processing unit and can perform more than one instruction at the same time Memory Whenever a computer needs to store data it goes here. Generally, this refers to Random Access Memory (RAM). It’s easily changed and volatile 2 . It stores data by assigning it an address . Secondary Storage It’s long term storage for large amounts of data and is non-volatile and cheaper than RAM but it’s much slower. Magnetic : More vulnerable to damage from magnetic fields, heat, impact, and natural deterioration over time. It’s heavier and bulkier than optical and solid-state media, and stores up to TBs of data. It’s cheap per GB, and is slower than solid state media. E.g. Hard disk Optical : More vulnerable to damage from scratches and natural deterioration over time, but more resistant to heat and impact. It’s portable as it’s small and light, but only stores up to GBs of data. It’s cheaper than SSDs per GB, but more ex than magnetic media, and slower than solid state media e.g. digital versatile disk (DVD) Solid-state : Most vulnerable, and most resistant to impact and temperature changes. It’s portable and lightweight due to it being small and light, and can store up to TBs of data. It’s the most expensive per GB, but faster than all other media. E.g. Solid-state drive (SSD) Data bus Bi-directional , transports data between CPU and memory Address bus Uni-directional , specifies memory address info. So when the processor wants to access data on say address 2, the processor 2 Data is lost if power supply is interrupted 1 Don’t write this tho, its not in tb and is very informal 2

will send 2 on the address bus, the data bus will return the data on address 2 in the memory to the processor. If the processor wants to override / update data at address 2, it will send data down the data bus and 2 on the address bus. The memory then updates address 2 with the data from the data bus