3 - hardware Flashcards
primary memory
can be accessed directly from the CPU
RAM
Random Access memory
- can be written to and read from
- stores files/ data currently in use
- volatile (memory contents are lost powering off the comp)
- can increase size to improve operational speed
ROM
- non volatile
- permanent memory (can’t change contents)
- stores data the comp uses when powering up (BIOS/ bootstrap)
DRAM
dynamic RAM
- capacitors hold the bits of information
- transistors act like switches and allow chip to control circuit to read/ write the capacitor
- needs to be refreshed constantly - if not charge will leak away leaving it with 0
+ cheaper
+ consume less power
+ higher memory capacity
used by main memory
SRAM
uses flip flops which hold each bit
+ doesn’t need to be refresehd
+ faster
- if accessed at a high freq power usage can exceed a DRAM
memory cache generally uses SRAM for this reason
PROM - Programmable ROM
- can be altered once
- made of a matrix of fuses
- uses electric current - burns fuses to alter specific cells
eg mobile phones, RFID tags
EPROM - Erasable Programmable ROM
- use floating gate transistors and capacitors not fuses
- UV light programs it through a quartz window
eg new games consoles, apps under development
EEPROM -electrically erasable programmable ROM
- electrical signal can be used to remove existing data
+ chip can remain in the circuit while contents are changed
buffers
- ## temporary storage for data transmitted from one part of the system to another which functions as a queue
embedded systems +
+ small so easy to fit
+ low cost
+ dedicated to one task - simple interface - no OS
+ consume little power
+ very fast reaction to changing input
+ mass production so reliable
embedded systems -
- difficult to upgrade devices - with new tech
- fixing it is specialist
- interface can be simple but in reality it can be confusing
- open to hackers and viruses
- due to difficulty in upgrading and fixing devices are throw away - wasted
embedded system
A computer system with one dedicated task ( no multitasking)
hard for the user to update
built in hardware and software
magnetic storage - HDD
- has platters - that spin
- has read/write arm
- data stored on surface in sectors and tracks
- magnetic field determines binary value
latency
time it takes for a specific block of data on a data track to rotate around to the read-write head
removable hard disk drives
are HDDs that are external to the comp and can be connected to the comp using a USB port
magnetic storage +/-
+ large storage
+ cheap
+ fast read/write
- lots of parts
- not durable
- sealed unit ( cant fix easily)
- not portable
solid state storage - SSD
- sends current which forces electrons through a barrier
- and traps them in floating gates
- binary data is stored by the held electrons
(flash memory)
SSD +/-
+ reliable - no moving parts
+ lighter
+ less power consumption
+ run cooler than HDDs
+ access data faster
- expensive
- unknown longevity
optical storage - CD DVD
- is a disk - with a spiral track
- binary represtented using pits/lands
- laser shines on - pits reflect light differently to determine binary value (read)
- laser makes indents on disk (write)
dual layering
used in DVDs to increase storage capacity
2 layers which are joined together
- shorter the wavelength of laser light the greater the storage capacity of the medium
- can cause birefringence (light is refracted into two beams causing reading errors)
blu-ray
- uses blue laser (shorter wavelength)
- blue light means pits and bumps can be much smaller (can store more)
- uses a single thicker disk - no birefringence
- automatically come with encryption
laser printers
- use dry powder ink and static electricity
- ## use blue cyan magenta black - print all in one go
inkjet printers
- nozzles spray ink onto paper
- has a stepper motor and belt which moves the print head across the page
- a paper feed which feeds the printer with pages as required
- thermal bubble of piezoelectric
thermal bubble
- tiny resistors create localised heat which makes the ink vaporise
- causes the ink to form a tiny bubble, as the bubble expands some of the ink is ejected from the print head onto the paper
- when the bubble collapses, a small vacuum is created which allows fresh ink to be drawn into the print head
- this continues until the printing cycle is completed.
piezoelectric
– a crystal is located at the back of the ink reservoir for each nozzle
- The crystal is given a tiny electric charge which makes it vibrate
- This vibration forces ink to be ejected onto the paper and at the same time more ink is drawn in for further printing.
3D printers
-solid object is built up using resin, metal or ceramic
speakers
- passed through DAC
- passed through amplifier to create larger current
- electric current is then fed to speaker
- current fed into wire - wire wrapped round core - interacts with magnet
- vibrates creating sound waves
microphones
- diaphragm in the mic vibrates
- coil is wrapped around magnet - coil is connected to the diaphragm using a cone
- cone moves in and out causing the copper coil to move backwards and forwards.
- causes the magnetic field around the permanent magnet to be disturbed, inducing an electric current.
- current is then either amplified or sent to a recording device
keyboard
- allows test input
- key press converted into character code
- transmitted to a processor
- processor displays character on screen
screens
- use LCD backlit with LED or OLED (organic light emitting diode)
- OLED - give off light when electricity applied to electrodes
- each screen pixels is made up of 3 sub pixels RGB
capacitive touchscreens
- made up of layers of glass acting as a capacitor creating electric fields between glass layers
- When the top layer is touched, the current changes - location is calculated by microprocessor
+ medium cost
+ good visibility
+ multi touch
+ durable - only allows bare fingers
resistive touchscreens
- makes use of upper and bottom layer
- when touched layers touch making complete circuit
- signals are sent out which are interpreted by microprocessor
+ cheap
+ can use any touch - bare, gloved fingers - poor visibility
- no multi touch
- not durable
virtual headsets
- video sent from a comp to headset
- two feeds are sent to an LCD/OLED - one for left and right - lenses reshape video making it 3D
- when user moves head sensors measure movement
- use binaural sound (surround sound
- some use infrared sensors to monitor eye movement
sensors
- are input devices which read or measure physical properties such as temp pressure acidity etc.
- uses ADC - converts physical values into digital values
- microprocessor analyses data
- if outside acceptable range alarm is raised or signals sent to control valves
anti-lock braking system
use magnetic field sensors to stop the wheels locking if they have been applied too sharply
- when one of the car wheels rotates too slowly data is sent to microprocessor
- checks rotation of other wheels - changes it to match others
- constantly being checked to prevent locking
latency
lag in a system egg time to find track on a disk
flash memory
a type of EEPROM suited to use in SSDs
logic gate
take binary inputs and produce an output
logic circuit
several logic gates combined for a specific function
NOT
triangle shape
if A is TRUE- X is NOT TRUE
X = NOT A
X = A ̅
AND
D shape
if A is TRUE and B is TRUE - X is TRUE
X = A AND B
X = A.B
OR
)D shape
if A is TRUE OR B is TRUE - X is TRUE
X = A OR B
X = A + B
NAND
Dº shape
is A is NOT T or B is NOT T - X is T
X = A NAND B
X = ̅A.B ̅
NOR
)Dº shape
if A is NOT T and B is NOT T - X is T
X = A NOR B
X = ̅A+B ̅ ̅ ̅
XOR
))D shape
X= 1 if (A is 1 AND B is NOT 1) OR (A is NOT 1 AND B is 1)
X = A XOR B
X = A ⊕ B
truth table
trace the output from a logic circuit
all possible input combinations are considered
