Module 5.6-5.7 Basic computer structure and microprocessors

Knowledge levels

Item	A	B3	B1	B2 / B2L
5.6(a) Computer terminology (bit, byte, software, hardware, CPU, IC, RAM, ROM, PROM) and computer technology in aircraft	1	1	2	2
5.6(b) Computer operation, layout, buses, instruction words, memory terms and devices, data storage	—	—	—	2
5.7 Microprocessors: functions, control and processing unit, clock, registers, ALU	—	—	—	2

All categories need the terminology in 5.6(a); the internal workings are B2/B2L only.

Terminology

Term	Meaning
Bit	binary digit, 0 or 1
Byte	8 bits; word = the number of bits the processor handles at once (8, 16, 32, 64)
Hardware	the physical parts (chips, boards, displays)
Software	programs (instructions) and data; firmware = software stored in non-volatile memory inside hardware
CPU	central processing unit - fetches, decodes and executes instructions
IC	integrated circuit - many components on one chip
Kilo/Mega/Giga byte	in computing, often powers of 2: 1 KiB = 1 024 bytes

Memory devices

Memory	Volatile?	Written how	Use
RAM (random access memory)	yes - lost when power is removed	read/write in operation	working data; SRAM (fast, flip-flop based) and DRAM (capacitor based, needs refresh)
ROM (read only memory)	no	programmed at manufacture	fixed programs
PROM	no	programmed once by the user
EPROM	no	erased by ultraviolet light through a window, then reprogrammed	older avionics
EEPROM / Flash	no	erased and rewritten electrically, in the unit	field-loadable software, databases, configuration
NVRAM	no	RAM with battery or non-volatile back-up	fault history, settings

Key fact: RAM is volatile; ROM, PROM, EPROM, EEPROM and Flash keep their contents without power. Flash/EEPROM allows software loading on the aircraft (5.13).