What is the purpose of secondary storage
to store data/files/ long term data
What is the need for primary storage?
- To store boot-up insturctions
-To store immediate/current data being calculated
What is an embedded system.
A microprocessor is a combination of hardware and software designed for a specific function within a larger system that performs a specific task.
Feautres of an embedded system.
Has memory,
input/output abilities.
processor integrated into machine,
not easily changed (by user/owner)
does not have its own operating system
Does not require much proccessing power.
What are disadvantadges of an embedded system.
- difficult to change/update firmware by user // difficult to upgrade to take advantage of new technology
- cannot be easily adapted for another task
- difficult to update or repair - usually thrown away instead
How does a laser printer work?
- contains a revolving drum that is given an electrical
charge - contents of page (provided by buffer/user) are drawn on drum as an electrostatic charge by a laser beam that moves back and forth
- the drum is coated with oppositely charged toner which only sticks to areas charged by the laser beam
- the drum then rolls over electrostatically charged paper, transferring the pattern onto the page
- paper is passed through a fuser/is heated to seal image
- the electrical charge is removed from drum, excess toner is collected
How does a 3D printer work?
- additive manufacturing
- uses digital 3D model or CAD file
- builds up model one layer at a time - starting from bottom, using xyz coordinates
-Filament on the wheel and is fed into the head of the printer into the nozzle.
-Filament is injected into the nozzle, while the nozzle heats up. Then the melted filament is dispensed. - material is fused together layer by layer
How does a microphone work?
- has a diaphragm
- incoming sounds waves cause vibrations about diaphragm
- this causes coil to move past a fixed magnet
-the coil cuts the field lines of the magnetic inducing a voltage, - electrical signal is produced
-The electric current generated is then digitised using ADC
How do speakers work?
- an electric current is sent to speaker
- the electric current passes through a coil
- current in the coil creates an electromagnetic field
- an electromagnet is repelled by, or attracted to the permanent magnet based on direction of the current in the coil
- movement of coil causes the diaphragm to vibrate - this vibration creates sound waves
How does a magnetic disk drive work, read and write ?
Magnetic Hard Disk
* has platters - divided into sectors and tracks
* surface of disk can be magnetised
* has a read/write head mounted on an arm
* data is encoded as a magnetic pattern
* writing - variation in current in head causes variation in magnetic field on disk
* reading - variation in magnetic field causes variation in current through head
Advantadges of a magnetic disk drive?
Advantages
* costs less per unit storage (used when large storage capacity is required)
* has more longevity (used with devices that work all the time and have large number of read write operations)
Solid State Memory
* uses a grid of columns and rows (arrays/blocks) that has two transistors at each
intersection:
* floating gate - stores voltage (represents either a 1 or 0)
control gate - controls movement of charge/electrons during read/write operations
* not possible to overwrite existing data (need to erase first then write data into location)
How does a solid state drive work
- Data is stored in NAND flash memory cells
- Made up of control and floating transistors
- Each cell uses a transistor with a floating gate
-Control gates control the flow of electrons in and out floating gates
-Floating gates hold/store the electron/voltage
Advantadges of solid state drive.
Advantages
- no moving parts - more reliable
- faster data access times
How is SDD non volatile (explain how it stores data)?
-High voltage is applied to the control gate
-The control gate then forces them into the floating gate
- The floating gate keeps the electrons in position.
- Therefore the storage is non-volatile
How does optical Disk work
- a rotating disk with tracks made from a reflective metal layer
- data is read/written using laser light (either red or blue) that is shone onto the disc and creates pits.
- data is stored in pits and lands on the track
- reading - reflected light from different states is encoded as a bit pattern
How can you re-write a disk
- remove the whole layer of pits then re shine laser to ingroove pits.
Uses of Optical disk
- used for transferring data between devices or as back-up systems
- can be read-only - used to distribute software, movies or games
- generally have lower storage capacity
How does a touch-screen work (resistive and capacitive)
Resistive touch screen
* has two layers
* when user touches screen, layers touch and a circuit is completed
* processor determines horizontal and vertical point of contact
* will work if any object touches the screen
Capacitive touch screen
* has several layers
* when top layer is touched, there is a change in the electric current
* a microprocessor identifies the coordinates of touch
How does a virtual reality headset work?
- video/data is sent from a computer to the headset
- the video feed is sent to an LCD/OLED display
- there are two lenses placed between eyes and screen - allows for focusing and reshaping of video for each eye, creating 3D effect
- uses an fps of 60 to 120 sensors measure/track movements of user, allowing the video on the screen to react to and mimic movements
- uses surround sound so sound from speakers appears to come from all directions
- can also use infrared sensors to monitor eye movement, allows depth of field on screen to be more realistic
What is the purpose of a buffer and how does it work
Purpose of a buffer
- A buffer is a small temporary storage area in memory (usually RAM) used to hold data while it is being transferred from one place to another.
- To act as temporary storage until it is ready to be transmitted to the device
-The data that is being transferred goes into the buffer and waits until it can be sent to the transferred device
- Reduces waiting time and prevents data loss
- It is used when devices operate at different speeds, allowing the faster device to continue working without waiting for the slower one.
- Allows processes to operate independently of each other.
How does buffer work
- instructions and data are sent by computer to buffer
- data is transferred from buffer to device - allowing the user to continue using the computer, allowing the processor to continue processing
- When the buffer is empty, an interrupt is sent to the computer, requesting more data
What is RAM, what does it do? What does it store?
- primary memory
- stores currently running part of software/data/OS/programs/processes
- either static or dynamic
- can store data about I/0 devices, contents of buffer, or information about current process
How does SRAM and DRAM work
SRAM - transistors arranged as flip-flops, more complex circuitry
DRAM - uses (a single) transistors and capacitors, stores bits as a charge
