Hardware

• Input, output, primary memory and secondary (including removable) storage each have a distinct role.
• Embedded systems are computers built into a larger device to do one dedicated job.
• The principal operations of laser and 3D printers, microphones, speakers, hard disks, flash memory, optical discs, touchscreens and VR headsets.
• Buffers hold data temporarily to make up for the speed difference between devices.
• RAM is volatile read–write memory; ROM is non-volatile. SRAM is fast and used for cache; DRAM is dense, cheaper and used for main memory.
• PROM is written once; EPROM is erased with UV light; EEPROM is erased electrically.
• Monitoring systems only observe; control systems use feedback from sensors to drive actuators.
• NOT, AND, OR, NAND, NOR and XOR: their symbols, functions and truth tables; converting between problem statement, circuit, truth table and expression.

What each part of a computer is for

Input devices get data into the computer; output devices present results. Primary memory (RAM and ROM) is directly accessible by the processor and holds the data and instructions currently in use. Secondary storage (hard disk, SSD) is non-volatile and keeps programs and data when the power is off; it is needed because RAM is volatile and limited. Removable storage (USB flash drive, memory card, optical disc) lets data be moved between computers and kept as an off-site backup.

An embedded system is a microprocessor-based system inside a larger device, performing one dedicated task: washing machine, microwave, car engine management, router, smart thermostat.

Describe the steps in order

• Laser printer: a drum is given a positive charge; a laser scans the drum and removes the charge where the image is not (or reverses it), leaving an electrostatic image; negatively charged toner sticks to the charged areas; paper is given a stronger charge and rolled past the drum so the toner transfers; a fuser (heated rollers) melts the toner onto the paper; the drum is discharged and cleaned.
• 3D printer: a 3D design (CAD) is sliced into thin horizontal layers by software; the printer builds the object one layer at a time, for example by extruding melted plastic through a heated nozzle that moves in x and y, then lowering the bed (or raising the nozzle) for the next layer.
• Microphone: sound waves make a diaphragm vibrate; a coil attached to it moves in a magnetic field (or the capacitance changes), producing a varying electrical signal; an ADC converts it to digital.
• Speaker