3.1. Computers and their components Flashcards
1
Q
Input
A
Take in data from the outside world
2
Q
Output
A
Display data for humans’ understanding
3
Q
Primary storage
A
Computer’s main memory which
stores a set of critical program’s instructions & data
4
Q
Secondary storage
A
Non-volatile storage for noncritical
data that will not be frequently accessed
5
Q
Removable secondary storage
A
- File backup and archive
- Portable transfer of files to second device
6
Q
Embedded systems
A
- Small computer systems such as microprocessors
that are often a part of a larger system - Each embedded system performs a few specific
functions unlike general-purpose computers
7
Q
Benefits of embedded systems
A
- Reliable since there are no
moving parts - Require less power
- Cheap to mass-produce
8
Q
Drawbacks of embedded systems
A
- Difficult to program functions since there is either no interface
- Expensive expert help
needed for repair
9
Q
Laser printer
A
- A laser beam and rotating mirrors are used to
draw image of the page on a photosensitive drum - Image converted into electric charge which
attracts charged toner such that it sticks to image - Electrostatic charged paper rolled against drum
- Charge pulls toner away from drum and onto
paper - Heat applied in the fuser to fuse toner to the
paper - Electrical charge removed from drum and excess
toner collected
10
Q
3D printer
A
- Process starts from saved digital file that holds the
blueprint of object to be printed - Object is then built by sequentially adding layers
of a material (e.g. polymer resin) until object
created - Object is then cured (e.g. resin-made objects are
hardened by UV light)
11
Q
Microphone
A
- Incoming sound waves enter wind screen and
cause vibrations about a diaphragm - Vibrations cause coil to move past a magnetic core
- Electrical current generated which is then digitized
12
Q
Speaker
A
- Takes electrical signals and translates into physical
vibrations to create sound waves - Electric current in voice coil generates an
electromagnetic field - Change in digital audio signal causes current
direction to change which changes field polarity - Electromagnet is either attracted or repelled to a
permanent magnet, causing a diaphragm that is
attached to the coil to vibrate - Vibration transmitted to air in front of speaker
- Degree of vibration determines amplitude and
frequency of sound wave produced
13
Q
Magnetic Hard Disk
A
- Hard disk has platters whose surfaces are covered
with a magnetisable material. - Platters are mounted on central spindle and rotated
at high-speed - Surface of platters divided into concentric tracks &
sectors, where data is encoded as magnetic patterns - Each surface is accessed by read/write heads
- When writing, current variation in head causes
magnetic field variation on disk - When reading, magnetic field variation from disk produces current variation in read head
14
Q
Solid State (Flash) Memory
A
- Most use NAND-based flash memory
- Consist of a grid of columns & rows that has 2
transistors at each intersection - Two transistors:
Floating Gate: stores electros and the presence or
absence of charge (electrons) represents either 1 or 0
Control Gate: controls charge (electrons) flow for
read/write
15
Q
Optical Disc Reader/Writer
A
- Disc surface has reflective metal layer and is spun
Tracking mechanism moves laser assembly - Lens focuses laser onto disc
- Laser beam shone onto disc to read/write
- Tracks have sequences of amorphous and crystalline
states on the metallic layer - When reading, the reflected light from the different
states on the track are encoded as bit patterns - When writing, laser changes surface to crystalline and
amorphous states along the track, which correspond
to 1s or 0s.
16
Q
Touchscreen
A
- Considered as both an input & output device
- Resistive or Capacitive
17
Q
Resistive Touchscreen
A
- Consists of two charged
plates - Pressure causes plates to
touch, completing circuit - Point of contact registered
with coordinates used to
calculate position
18
Q
Capacitive Touchscreen
A
- Made from materials that
store electric charge - When touched, charge
transferred from finger
19
Q
Virtual (Reality) headset
A
- Virtual headsets consist of 2 lenses, (LCD) display,
circuit board with sensors, cover and foam padding - The display provides a simulation of a 3D
environment, generated by a 3D graphics package - The user can ‘move’ in the virtual environment by
moving their head or using controllers
20
Q
Buffers
A
Short-term memory storage that stores data right
before it’s used, typically in RAM.
21
Q
RAM
A
- Volatile memory: loses
content when power turned
off - Can be read and altered
- Used to store currently
executing program
22
Q
ROM
A
- Non-volatile memory: does
not lose content when power
turned off - Can only be read
- Used for storing OS kernel
and boot up instructions
23
Q
SRAM
A
- Doesn’t need to refresh
hence uses less power and
faster access time - Doesn’t need to refresh
hence uses less power and
faster access time - Each bit stored in flip-flop
- Has lower data density
- Used in cache memory
24
Q
DRAM
A
- Has to be refreshed, hence
has slower access times and
needs higher power - Only single transistor &
capacitor, hence less
expensive to purchase - Each bit stored as a charge
- Has higher data density
- Used in main memory
25
PROM
* Programmable ROM
* Can be programmed only once after it is created
* Data cannot be erased or deleted
26
EPROM
* Erasable Programmable ROM
* Can be erased by UV light exposure and can then be reprogrammed
* Chip has to be removed for Reprogramming
27
EEPROM
* Electrically Erasable Programmable ROM
* Can be erased by an electrical signal and can then be reprogrammed
* Can update data without removing chip.
28
Monitoring System
* Monitors some state external to computer system
* No changes made to environment by the system
and hence no feedback
29
Control System
* Regulates the behaviour of other devices or
systems.
* Event-driven system: the controller alters the state
of the system in response to some event.
* Time-driven system: the controller takes action at
a specific point in time
30
Hardware typically used in a system
* Sensor: measures an (analogue) property and
transmits it to a processing unit, generally as an
electrical or optical signal.
* Actuators: switch on/off heavy appliances (e.g.
heater to heat/fan to cool)
* ADC: converts analogue signals to digital signals
* Transmission cable: to transfer signals
31
Feedback Systems
* Output from system affects the input of sensors.
* Ensures system operates within the given criteria
* By enabling the system output to affect
subsequent system inputs, it may cause a change
in the actions taken by the system
* Thus enables the system to automatically adjust
conditions in a continuous process
