Title: Year 12 / Computer Science / Theory / 3 - Hardware / 3.1 - Computers and their components

Q: Describe what is meant by an embedded system
A: microprocessor within a larger system or microprocessor that performs one specific task

Q: State the advantages of using embedded systems
A: special purpose, they perform only one function
economies of scale, the more you make the cheaper they become

Q: State the disadvantages of using embedded systems
A: if errors are found, then new chips have to be manufactured
if installed with an internet connection, then less protected against unlawful actions
its not easy for the owner to update

Q: State an example of primary storage
A: RAM, ROM

Q: State an example of secondary storage
A: hdd, ssd, usb flash drive, optical disk, floppy disk

Q: State the difference between RAM and ROM
A: RAM is volatile, ROM isnt
in RAM data can be read or written to so can be altered, in ROM data is read only and cant be altered
RAM's memory size is larger

Q: Describe what is meant by volatile
A: contents are lost when the power is turned off

Q: State what RAM is used to store
A: operating system
data and files currently in use

Q: State what ROM is used to store
A: BIOS or computing startup instructions

Q: Explain why input is needed
A: input devices have to feed data into a computer or microprocessor so that it can be processed

Q: Explain why output is needed
A: due to processing of data, a microprocessor can deliver a response, which has to be done through actuators or output devices so that it can be output to the user for human understanding

Q: State 4 examples of input devices
A: keyboard
mouse
microphone
camera
bar code scanner
sensors

Q: State 4 examples of output devices
A: monitor
printer
plotter
speakers
actuators/motors
projectors
headphones

Q: Describe what is meant by primary storage
A: storage where data and critical program's instructions that has to be accessed by cpu immediately is stored temporarily

Q: Describe why primary storage is needed
A: since its accessed by cpu, it allows data and instructions to be executed quicker than if they were stored elsewhere

Q: Describe what is meant by secondary storage
A: long term, non volatile form of storage used to store data and files on the computer permanently

Q: Describe why secondary storage is needed
A: too much data and files to store on the primary storage alone

Q: Describe the principal operations of a magnetic hard disk
A: application program executes instruction to read file, so passes file read request to os, os spins hard disk, in correct directory file, os looks up track and sector where file begins, head moves to correct track, hdd waits for correct sector to arrive under head, head reads first cluster of heads from disk and writes to disk buffer, when hdd has read file, generates interrupt, os transfers contents of buffer to application programs data memory

Q: Describe the principal operations of an optical disk
A: drive motor used to spin disk, tracking mechanism moves laser assembly, lens focuses laser onto disk, laser beam shone on disc to read or write, surface of disk has reflective metal layer, track on disk have sequence of pits and lands, reflected light is then encoded as bit pattern

Q: Describe the difference in principal operations of a recordable optical disk and a re writable one
A: they use different techniques to achieve a differential between a pit and a land
recordable formats use a transparent dye that becomes opaque when heated by a laser
re writable formats use a laser to change the state of a phase change alloy and a magnet to set a new state

Q: Explain why CDs, DVDs and BluRay have different capacities despite all of them having the same physical size
A: different laser wavelengths burn smaller pits,
the spiral track can be more tightly wound, which creates a longer track

Q: Describe the principal operations of solid state memory
A: uses grid of columns and rows that has 2 transistors at each intersection, one is called floating gate, other called control gate, memory cells store voltages which represents either 0 or 1, electron movement controlled to read and write, isnt possible to overwrite existing data

Q: State the advantages of using an SSD over a traditional hard disk
A: faster access speed as there are no moving parts
lower power consumption, so more battery life in portable devices and devices stay cooler
less likely to be damaged
silent
lighter
larger capacity
reliable
non volatile

Q: Explain the use of buffers
A: region of memory shared by hardware devices or programs that operate at different speeds, used to temporarily store data while its moved from 1 place to another, allows each device or process to operate without being held up by another

Q: Describe why removable secondary storage is used
A: file backup and archive, portable transfer of files to second device

Q: Explain what is meant by SRAM
A: more complex circuitry, more than 1 transistor, doesnt need to refresh as transistors hold data as long as power supply on, faster access time, stores each bit using flip flop, uses less power, more expensive, lower storage and bit density, used in main memory

Q: Explain what is meant by DRAM
A: requires data to be refreshed often to retain data, requires higher power consumption (significant in battery powered devices), uses 1 transistor and capacitor, stores each bit as a charge, slow access time, less expensive, higher storage and bit density

Q: Explain what is meant by PROM
A: programmable read only memory, can only be programmed once after manufacture, program or data once installed cant be changed

Q: Explain what is meant by EPROM
A: erasable prom, can be reprogrammed using UV light by erasing installed data and installing new data or program, chip has to be removed before reprogramming

Q: Explain what is meant by EEPROM
A: electrical erasable PROM, can be reprogrammed using electricity, electrical signal is used to remove existing data, benefit is chip can remain in circuit before reprogramming, but chip used as read only

Q: Describe what is meant by a monitoring system
A: monitors some state external to computer system, no changes made to environment by system so no feedback

Q: Describe what is meant by a control system
A: regulates behaviour of other devices or systems

Q: Describe what is meant by an event driven system
A: controller alters state of system in response to an event

Q: Describe what is meant by an time driven system
A: controller takes action at a specific point in time

Q: Describe the function of a sensor
A: measures an analogue property and transmits it to processing unit, usually as electrical or optical signal

Q: Describe the function of actuators
A: switch on/off heavy appliances, like heater to heat or a fan to cool

Q: Describe the function of ADC
A: converts analogue signals to digital signals

Q: Explain how a feedback system works
A: ensures system operates within given criteria, enables system output to affect subsequent system input of sensors so that it may change actions system takes

Q: Explain the importance of a feedback system
A: enables system to automatically adjust conditions in a continuous process

Q: Describe the principal operations of speakers
A: takes electrical signals and translates it into physical vibrations to create sound waves, electric current in coil creates electromagnetic field, change in audio signal causes direction of electric current to change, which changes polarity of electromagnet, electromagnet repelled or attracted to permanent magnet, causes coil to vibrate, which causes cone to vibrate, vibration transmitted to air as sound waves, amount of movement determines frequency and amplitude

Q: Describe the principal operations of a microphone
A: has diaphragm, incoming sound waves cause vibrations of diaphragm, causing coil to move past magnet, which causes an electrical signal to be produced

Q: Describe the principal operations of a 3D printer
A: 3d design split into layers, data for first layer transmitted into 3d printer, printers work by interpreting a set of instructions that model an object in 3d space, plastic filament extruded at heat and applied to precise dimensions and location where layers are added sequentially until object created, object is then cured/hardened

Q: Describe the principal operations of a laser printer
A: laser beam and rotating mirror used to draw image of page on photosensitive drum, image converted into electrostatic charge, which attracts toner, charged paper then rolled against drum, opposite charged paper picks up toner particles from drum, paper passes through fuser, so paper heats up, toner melts and forms permanent image on paper, electrical charge removed from drum and excess toner collected

Q: Describe the principal operations of a virtual headset
A: contains 2 eye pieces, which are fed paired images from controlling system which gives eyes sensation of being in 3d environment, images can be collected using 3d graphic package, user of headset can control which part of environment they view by moving their head or a controlling device

Q: Describe the principal operations of a resistive touchscreen
A: consists of 2 charged plates, pressure causes plates to touch, which completes the circuit, point of contact gets registered, coordinates used to calculate position

Q: Describe the principal operations of a capacitive touchscreen
A: made from materials that store electric charge, when touched charge transferred to finger, sensors at screen corners detect change, point of contact registered, coordinates used to calculate position

Q: Describe the benefits of using a magnetic hard disk
A: inexpensive per unit of storage, large storage capacity to store videos of large size, fast access speed, users dont have to wait for video to load, doesnt need to be moved, so no damage to moving parts, slower degradation of data, will last longer