Chapter 3 - Hardware Flashcards
1
Q
Is a thermometer a sensor+why
A
No, it is a tube filled with alcohol or mercury that can be read by a human eye in comparison to a scale, computers cannot see the level so it needs something else.
2
Q
Whast sensor do you use to measure motion
A
Infra-red
3
Q
What sensor do you use to measure temperature
A
Temperature sensor
4
Q
Where would you use a pH sensor
A
In a pool
5
Q
Where is an acceleromenter used
A
In a car
6
Q
What are sensors
A
Input decives that can read or measure physical properties from their surroundings.
7
Q
Explain real data+1 eg,
A
Real data is anologue in nature, meaning that there are infinite no of values and the data requires interpretation/best judgemnent from user
Computers cannot make sense of real data
Thermometer
8
Q
What is an ADC
A
An Anologue Digital Converter
Takes real life data/physical quantities and converts them to digital format/discrete digital values.
9
Q
What is a DAC+eg of when they are used
A
Digital to anologue converter
When a computer is used to control devices eg.valve
Actuators are used
10
Q
What is an actuator
A
A device that helps achieve physical movements by converting energy to mechanical force
11
Q
What is feedback
A
When the output readings of a sensor are recieved by the microproccessor and may impact the next input to bring the system within the desired parimetres.
12
Q
What are the 2 types of applications for sensors
A
Monitoring and control
13
Q
Explain monitoring sensor use+eg.
A
If the new data recieved is outside the acceptable range,a warning message/alarm appears
The microprocessor/computer has no effect on what is being monitored, they simply observe and notify
Pollution in river
14
Q
Explain sensor applications:control
Eg.
A
If the new data recieved is outside the acceptable range, the computer/microprocessor sends signals to control aspects of the system/device. Output from the system affects the next set of inputs (feedback loop)
Chemical process control(maitnaining pH)
15
Q
What is the difference between active infra-red and passive infra-red
A
Active uses an invisible beam of infrared radiation that when broken changes the amount of radiation reaching the detector (wind screen wipers)
Passive has sensors measure he heat radiation given off by an object (security alarm system)
16
Q
Where are magnetic field sensors used
A
Anti-lock braking systems
17
Q
What does the CPU consist of (3/4)
A
CU-control unit
ALU- arithmetic and logic unit
Registers and buses
18
Q
What is a CPU
A
Central processing unit
Responsible for execution/processing of all instructions and data in s computer
Often installed as an integrated circuit on a microchip
19
Q
What did John van Neumann do
What features did it have
A
Developed a stored program computer in the 1940’s
Concept of CPU
CPU could access RAM directly
Memory could store programs and data
Stored programs were made up of data in sequential order
20
Q
What are the main components of the CPU (3)
A
ALU-arithmetic and logic unit
CU-control unit
Registers
21
Q
Purpose of ALU in the CPU
A
Allows arithmetic, logic and or operations to be carried out whilst a program is being run
There can be more than one ALU to carry out specific functions
22
Q
What does the CU in the CPU do
A
Reads instruction from memory/controls flow of information
Address of location where instruction is found is stored in the PC (program counter)
Generates command signals along control bus
System clock is used to produce timing signals for^(without system would crash)
23
Q
How is the instruction from the PC interpreted
A
Fetch-decode-execute cycle
24
Q
Where + how does the CU access its data and programs
A
In the RAM/IAS(immediate access store)
The CPU takes data and programs held in a backing store and temporarily puts them into RAM
This leads to faster operations
25
What are registers function in CPU (3)
General or special purpose eg.
ACC-actuator(carries out ALU+temporarily stores data)
PC-program counter(stores address where next instruction is found)
MAR-memory access register(stores address of memory currently being read/written from)
26
How is the CPU installed
Installed as an integrated circuit on a single microchip
27
What is the responsibility of the CPU and what does it consist of
Responsible for the execution/processing of all instructions and data in a computer application
Control unit (CU)
Arithmetic and logic unit (ALU)
Registers and buses
28
What are the main components of the CPU
ALU
Registers
CU
System buses and memory
29
CPU
Central Processing unit
Responsible for the execution or processing of all the instructions and data in a computer
30
Integrated circuit
Chip made from a semi-conductor material which carries out the same tasks as a larger citcuit made from individual components
31
Explain briefly/simply how memory works in a computer
Memory is comprised of partitions with each partition being made up of adresses and contents, the address uniquely identifies every location in the memory and the contents are the binary value stored in each location
32
Specific purpose registers (5)
Current Instruction Register (CIR)
Accumulator (ACC)
Memory Access Register (MAR)
Memory data/buffer register(MDR)
Program Counter (PC)
33
Purpose of CIR
Current Instruction register
Stores the current instructions being decoded and excecuted
34
Function of RAM
Also known as the immediate access store (IAS)
Holds all the data and programs needed to be accessed by the CPU, which takes data and programs held in the backing store and temporarily puts them into RAM as read-write functions carried out using RAM will be a lot faster, key data needed by an application will also be stored in RAM to speed up operations
35
Backing store
Secondary storage device (HDD/SSD) used to store data permanently, even when the computer is powered down.
36
Role of the CPU in a computer
Process instructions and data input into the computer so that the result can be output
37
Purpose of ACC
Accumulator
Used when carrying out ALU calculations, temporarily stores data
38
Purpose of MAR
Memory Access Register
Stores the address of the memory location currently being read from or written to
39
Purpose of MDR
Stores data which has just been read from memory or data which is about to be written to memory
40
Role of PC
Program Counter
Stores the address where the next instruction can be read and found
41
System busses def + (3)
A connection between major components in a computer that can carry data, addresses or control signals
-Address bus
-Control bus
-Data bus
42
Describe read write operations with MDR and MAR
The address uniquely identifies the location in the memory
READ
Address of the location to be read from is first written into the MAR, a read signal is sent to the computer memory and the contents of this address are put into the MDR
WRITE
Data to be stored is first written to MDR
The data is written to a new address which is then written to the MAR. A write signal is sent and the value would then be written into the correct memory location
43
Address bus
system bus that carries addresses throughout the system. Unidirectional (1 way only) to prevent addresses being carried back to the CPU (not good)
44
Significance of the width of an address bus
The wider the bus, the more memory locations that can be simultaneously addressed. (2 to the power no. Of bits)
45
Data bus
System bus that allows data to be carried to and from CPU to memory/input/output devices as it is bidirectional.
46
Word
Group of bits used by a computer to represent a single unit, the larger a computers word length the greater the performance
47
Significance of the width of the data bus
The wider the larger the word length, the better the overall performance of the computer
48
Control bus
System bus that carries signals from control unit to all other computer components. Bi directional and usually 8. Bits in width as it on,y carries control signals.
49
How the Fetch-decode-execute-cycle is carried out in the von Neumann computer model
Checks for instructions, the PC contains the address of the memory location of the next instruction to be fetched. This address is copied from the PC to the MAR using the address bus. The contents at the address in the MAR are temporarily copied into the MDR. The content of the MDR is then copied and placed into the CIR. The value in the PC is incremented by 1 so that it points to the next instruction that has to be fetched. The instruction is decoded and executed by sending out signals via the control bus from the CPU to the various components of the computer system, if there’s more instructions to service the process repeats otherwise it ends.
50
Core
A unit on a CPU made up of an ALU, CU and registers. There can be multiple cores on a CPU
51
System clock
Produces timing signals on the control bus to ensure synchronisation takes place
52
Clock cycle
Measured in GHz
Vibrational frequency of the system clock which sends out pulses along the control bus. 3.5GHz is 3.5 billion clock cycles a second
53
IAS
Immediate Access Store
Memory that holds all data and programs needed to be accessed by the CU
54
Cache
Temporary Area of storage used to quickly access frequently used data.
55
Factors that affect the performance of the CPU (4)
Width of the address and data bus - increasing width increases performance + speed
Overlocking - increasing clock speed potentially increases speed of computer
Use of cache memories - the bigger the cache the faster the access time as it doesn’t have to go look through RAM
Number of cores - alleviates the need to increase clock speeds - must take into consideration the time taken to communicate with each core
56
Overlocking
2 problems
Changing the clock speed of a system clock by accessing the BIOS, to a value higher than the recommended setting.
-unsynchronised operations leading to frequent crashes
-overheating of CPU leading to unreliable performance
57
Dual core
Quad core
CPU containing 2 cores using 1 channels to communicate
CPU containing 4 cores using 6 channels to communicate
58
Instruction set
List of machine code instructions used by a particular microprocessor. List of machine code commands that can be processed by the CPU.
59
Purpose + use of an instruction set for CPU
The computer needs to be able to understand the operation to be carried out, so there are a limited number of opcodes to be used (the instruction set). Need to be converted into binary and instruction the CPU on how to carry out an operation. Eg. ADD
60
Opcode
Informs the CPU what operations need to be done
61
Operand
Part of a machine code instruction that identifies what data is to be used
62
Devices in which embedded systems are found (6)
Cars
Set-top box (recording + playing back TV programs)
Security systems
Lighting systems
Washing machines
Vending machines
63
Embedded system
Combination of hardware and software designed to carry out a specific set of functions.
Have a user interface, analogue/digital input and some form of output, mechanical components etc.
Can be based on microcontroller, microprocessor and system on chips (SoC)
64
Types of embedded systems (2)
Programmable (updates by connecting to computer + downloading or automatically via WiFi)
Non-programmable (need to be replaced if they need a software update)
65
Benefits of embedded systems (7)
Small, can easily fit into devices
Relatively low cost to make
Dedicated to one task therefore simple interfaces and no need for an operating system
Consumer very little power
Can be controlled remotely
Very fast reaction to changing input
With mass production comes reliability
66
Are computers embedded systems
No, they are multifunctional
67
Drawbacks of embedded systems (6)
Difficult to upgrade
Troubleshooting faults becomes a specialist task
Interface can be confusing
If accessible over the internet it is open to hackers or viruses
Wasteful, devices often thrown away due to difficulty upgrading
Leads to an increase in the throw away society when they become out of date
68
Barcode
Series of dark and light lines of varying thickness used to represent data. Code has to be scanned using. A laser or led light source. Most commonly found at the checkout of supermarkets
69
What happens when a barcode is scanned
Barcode is read by laser or LED
Light is reflected off the barcode (not off the dark lines)
The reflected light is read by sensors containing photoelectric cells
As the laser/LED is scanned across the barcode a pattern is generated and converted to digital data for the computer to understand. L=0, D=1
70
Input/output devices found at supermarkets + uses (6)
Keypad - key in weight/number of items/ barcode number if it failed to scan
Screen/monitor-show cost of an item
Speaker - beep when scanned correctly
Printer - print reciept
Card reader - read customers card using PIN or contactless
Touchscreen- select items by touching an icon
71
What happens when the barcode has been successfully scanned
The number is looked up in the stock data base (it is the key field in the item record)
When the number is found the stock item record is looked up
Price + other details are sent to the checkout point
Number of stock items reduced by 1
New value for stock is written back to the item record
Number of items compared to re-order level, if <= it is automatically ordered
A flag is added to the record to stop reordering each time that barcode is scanned
Upon arrival, stock levels are updated
72
Advantages to management of using barcodes (5)
Easier + faster to check prices
Up-to-date sales information
Saves time + cost of pricing every single item
Allows for automatic stock control
Possible to check customer buying habits
73
Advantages to customer of using barcodes (5)
Faster checkout queues
Errors in charging reduced
Itemised bill
Cost savings can be passed on to customer (lower sale price)
Better track of sell by dates (fresher food)
74
QR code
Another type of barcode, quick response code
Consists of pixels me can presently hold up to 4269 characters or 7089 digits and allows internet addresses to be encoded within the QR code. Has 3 squares in the corners that are used to ensure correct alignment and orientation when reading the code
75
Advantages or QR codes compared to traditional bar codes (5)
Hold more information
Fewer errors as the higher capacity allows built-in-error checking systems
Easier to read
Easier to transmit
Possible to encrypt providing greater protection
76
Disadvantages of QR codes compared to traditional barcodes (2)
More than 1 format is available
Can be used to transmit malicious code (at tagging)
77
Frame QR codes
QR codes being used because of the ability to add advertising logos in the “canvas area”
78
Digital cameras
Input device that are controlled by an embedded system which can automatically adjust the shutter speed, focus, operate the flashgun, adjust aperture size and image size and remove red eye
79
What happens when a photo is taken
Image is captured when light passes through the lens onto a light-sensitive cell which is made up of millions of tiny sensors acting as photodiodes. The image is converted into tiny electric charges which are passed through an ADC which converts electric charges from each pixel into levels of brightness to form a digital array. Sensors measure colours which forms another binary pattern. The number of pixels determines the file size used to store the photo and the quality depends on the number of pixels used, levels of light, storage and Len’s quality.
80
Keyboard
Most common method of data entry, input device that can be connected via USB or wireless or be virtual/touchscreen. Each character consists of an ASCII value which when pressed is converted into a digital signal for the computer to interpret. You get ergonomic keyboards to increase speed and reduce wrist strain
81
How a computer recognises a letter pressed on the keyboard
There is a membrane/circuit board on the base of the keys, when a key is pressed it makes contact with the bottom conductive layer completing the circuit allowing the CPU to determine which key has been pressed and refer to an index file to see which character the key represents
82
Microphone
(How it works)
Input device either built in or externally connected through USB port or Bluetooth.
When a sound is made the air vibrates, the vibrations are picked up by a diaphragm in the microphone which also begins to vibrate and move in and out, causing the copper coil wrapped around the cone to move forwards and backwards so it cuts through the magnetic field around a permanent magnet and induces an electric current (analogue in nature) which is then either amplified or send to a recording device.
83
Optical mouse
Example of a pointing device that can be used on any surface, uses tiny cameras to take 1500 images per second.
A red LED is used in the base of the mouse, when the light reflects off the surface it is picked up by a complimentary metal oxide semiconductor (CMOS) which generates electric pulses to represent the reflected red light which are sent to a digital signal processor (DSP). The processor works out the coordinates of the mouse based on the changing image patterns as it moves about the surface and the computer moves the cursor depending on these coordinates
84
Benefits of optical mouse over mechanical mouse (3)
Benefits of mechanical mouse (3)
No moving parts
Dirt can’t get trapped
No need for special surfaces
No signal loss as there is a constant signal pathway (wire)
Cheaper to operate (batteries)
Fewer environmental issues (batteries)
85
2D scanner
Converts the image into an electronic format that can be stored in a computer
86
Pointing device
Input device that allows the user to control the movement of an onscreen cursor by clicking a button on a device
87
CMOS
Complimentary Metal-Oxide Semiconductor
Chip that generates electric pulses/currents when light falls on a surface
88
Stages of scanning a document
Cover is raised, the document is placed on the glass panel and the cover is closed. A bright light illuminates the document and a scan head moves across until the whole page has been scanned. An image is produced which is sent to a lens, to focus the image, using a series of mirrors. The image then falls onto a Charge Couple Device (CCD) and the software produces a digital image from the electronic form. Computers equipped with Optical Character Recognition(OCR) allow the scanned text to be converted into a text file format.
89
CCD
Charge Couple Device
Device Made up of thousands of light sensitive pixels that create an electric charge when light falls on them, transferring a scanned image into digital form.
90
3D scanners
Scan solid objects and produce 3D images which can be used in Computer Aided Design or 3D printing to produce models.
91
Application of 2D scanners
At the airport, OCR technology and face recognition for checking passports
92
Application of 3D scanning
Computed tomographic (CT) scanners
Used to create a 3D image of a solid object based on tomographic technology which builds up an image of a solid object through a series of very thin slices built up by X-rays, radio frequencies or gamma imaging. Each slice is stored as a digital image and can be represented digitally in the computer memory
93
Touch screens
3 types
Screens that allow users to manipulate a screen image using touch or a stylus
Capacitive
Infrared
Resistive (most common)
94
Capacitative touch screens
Protective layer of glass, transparent electrode layer and a glass substrate. Human skin is a conductor of electricity, so when we or a stylus touch the screen the electrostatic field of the conductive layer is changed allowing the microcontroller to calculate the coordinates or the point of touching by calculating where the change took place.
95
Types +explanation of each capacitive tough screen (2)
Surface - sensors placed at the corners and small voltages are applied creating an electric field. When a finger touches the field it draws current from each corner reducing the capacitance which is measured by the micro processor to determine where the touch took place. (Stylus or finger only)
Projective - transparent conductive layer in the form of an X-Y matrix pattern which creates a 3D electrostatic field which is disturbed by a finger, thin gloves or stylus and allows the microprocessor to determine the coordinates of the point of contact. Allows multi touch facility (pinching, sliding)
96
Advantages of capacitive touch screens (3)
Disadvantages (2)
Better image clarity
Durable screens with high scratch resistance
Allows multitouch
Only work with bare fingers or special stylus
Sensitive to electromagnetic radiation
97
Infrared touch screens
Glass screen with an array of sensors around the edge, that detect infrared radiation being reduced by the infrared beams being broken (finger touching screen), and infrared transmitters that cover the screen in a matrix pattern. The readings are sent to the microprocessor to calculate where the screen was touch
98
Advantages of infrared touch screens (3)
Disadvantages of infrared touch screens (3)
Allows multi touch facilities
Durable
Operability is unaffected by a damaged screen
Sensitive to water/moisture
Possibility for accidental activation if the beams are disturbed
Sensitive to light interference
99
Resistive touch screens
2 layers of electrically resistive material with a voltage applied across them. Upper layer is made of flexible polyethylene with a resistive coating on one side and the other layer is made of glass with a resistive coating. The layers are separated by air or an inert gas, when the polyethylene surface is touched the layers make contact and a circuit is complete with results in the flow of electricity. The point of contact is detected by the change in voltage, which is converted to digital data by the microcontroller and sent to the microprocessor.
100
Advantages of resistive screens (2)
Disadvantages of resistive screens (4)
Good resistance to dust and water
Can be used with finger stylus or glove
Low touch sensitivity
No multi-touch facility
Poor visibility in strong sunlight
Vulnerable to scratches
101
Actuator
Output device that converts electrical energy to mechanical. Thing such as a solenoid, relay or motor.
102
Types of light projectors (2) + def.
Used to project computer output onto large screens or interactive whiteboards. Used in presentations.
-Digital light projector (DLP)
-Liquid crystal display projector(LCD)
103
DLP
Digital light projector
Uses millions of micro mirrors on a digital micro mirror device (DMD).
The number of micro mirrors and how they are arranged on the DMD chip determine the resolution of the image, when they tilt toward the light source they are on. Creating a light/dark pixel on the projection screen. A greyscale image is created by the mirrors switching on or off several thousand times a second. A bright white light source passes through a condensing lens, colour filter, shaping lens, the DMD chip and another lens before it is projected onto the screen.
104
MOEMS
Microoptoelectromechanical system
What a DMD chip is made of, contains thousands of microscopic mirrors of polished aluminium arranged on the chip’s surface, each mirror corresponds to a pixel
105
DMD
Digital micrometer device
Chip that uses millions of tiny mirrors on its surface to create a video display
106
LCD projector
Liquid crystal display
Powerful white beam of light generated from a bulb/LED which is sent to a group of chromatic coated mirros that reflect the light back at different wavelengths corresponding to RGB components. The components pass through a 3 LCD screens producing 3 images, one in red, blue and green. The images are recombined using a special prism and the image finally passes through the projector lens onto a screen
107
Advantages of DLP (6)
Higher contrast ratios
Higher longetivity
Uses single chip, no need to line up images
Smaller and lighter than LCD
Better suited to dusty/smoky areas than LCD
108
Disadvantages of DLP (3)
Has shadows when showing a moving image
Doesn’t have grey components
Colour definition isn’t as good
109
Advantages of LCD (3)
Sharper image
Better colour saturation
More efficient in energy use (generate less heat)
110
Disadvantages of LCD projector (3)
Contrast ratios aren’t as good
Limited lifespan
Panels degrade over time as they are organic in nature
111
How ink droplets are produced (2)
Thermal bubble - tiny resistors create localised heat which makes the ink vaporise and form a tiny bubble, the ink is ejected from the print head onto the paper as the bubble expands, and once it collapses a small vacuum is created which allows fresh ink to be drawn in and the cycle repeats until the whole page is printed
Piezoelectric- Crystal located at the back of the ink reservoir for each nozzle gets given a tiny electric charge causing it to vibrate forcing ink to be projected onto paper whilst more gets drawn in.
112
Inkjet printer components (4)
Print head
Ink cartridges
Stepper motor and belt
Paper feed
113
Steps in an inkjet process (9)
Data from document is sent to a printer driver
Printer driver ensures the data is in a format that can be understood
Printer driver checks to see if the printer is ready to print (paper, ink etc)
Data sent to printer buffer
Sheet of paper fed into main body, if the sensor does not detect this an error message is sent
As the sheet is fed the print head moves across the paper and sprays the 4 ink colours in exact amounts to produce the final image
At the end of each full pass the print head advances slightly to the next line
If there is more data in the printer, the cycle continues until the buffer is empty
Once the buffer is empty the printer sends an interrupt to the CPU to request more data to be sent and the process repeats until the document is printed
114
Steps in laser printer process (11)
Data is sent to printer driver
Driver ensures the data is in a format the printer can understand
Check is made to see if the printer is available
Data sent to buffer
Printing drum given a positive charge, rotates and a laser beam is pointed at it to remove the charge in certain areas to leave a negative charge to match the image
Drum coated with positively charged powder that only sticks to the negative areas
Negativity charged sheet of paper is rolled over the drum
Toner on the drum sticks to the paper to produce the image
Electric charge on the paper is removed after 1 roll to prevent sticking
Paper goes through a fuser (set of heated rollers) to melt the ink
Discharge lamp removes the electric charge from the drum
115
Use of inkjet printers
Use of laser printers
Printing one-off photos that require good quality colour printing
Fast, High quality printouts as they have large tonor cartridges and paper trays to hold more paper
116
Laser printers
Use dry powder ink and static electricity as opposed to liquid ink to produce text + images. Print the whole page in 1 go using 4 toner cartridges
117
Types of 3D printing (2)
Direct 3D printing - uses inkjet technology, the head moves left to right and up and down
Binder printing - requires 2 passes for each layer, 1st sprays dry powder and the 2nd a binder to form a solid layer
118
3D printers
Use additive manufacturing to produce solid objects that work. Make use of inkjet and laser technology, and allow the object to be built up layer by layer using powdered resin, metal, paper or ceramic
119
How to create a solid object using 3D printers (5)
Design using CAD computer aided design software
Import to special software that prepares it in a format to be understood by the 3D printer
Set up 3D printer
Object built up layer by layer often taking hours depending on the material and size of the object
Object is removed from the printer, some require cutting away of excess, emerging in water to remove a jelly-like support and then left to cure
120
Uses of 3D printing (4)
Prosthetic limbs
Car parts
Facial reconstruction parts
Aerrospace
121
LED screens
Made up of tiny LEDs either red, blue or green. Brightness of each LED is controlled through a varying current. Produces vast, brilliant colours.
122
LCD screens
Screens made up of tiny liquid crystals that make up an array of pixels affected by changes in applied electric fields. Require backlighting using LED technology as they don’t produce any light themselves. A matrix of tiny white-blue LED behind the screen gives a very good contrast and brightness range
123
CCFL
What LCD screens used as a backlighting method before LEDs
Cold cathode fluorescent lamp, 2 fluorescent tubes behind the LCD screen
124
Advantages of using LEDs as a backlighting method (6)
Immediately reach maximum brightness
Consume very little power
Give a white light that sharpens the image and makes the colours more vivid
Brighter light and therefore for better colour definition
Lasts indefinitely
Thin
125
OLED
Organic Light Emitting diodes
Use organic materials (carbon compounds) to create flexible semiconductors. Organic films are sandwiched between 2 charged electrodes (metal cathode glass anode) which give of light when a charge is applied to them eliminating the need for backlighting and allowing for very thin screens which can be bent and folded (galaxy fold)
126
Advantages of OLED screens (6)
Thinner lighter and more flexible
Can be made from plastic
Give a brighter light
Don’t require backlighting (use less power)
Can be made big
Large field of view (ideal for TV)
127
Loud speakers
How they work
Output devices that produce sound by the digital data being passed through a DAC to be changed into an electric current which is then passed through an amplifier and fed to a loudspeaker to be converted to sound.
128
DAC
Digital to analogue converter
Converts binary data to analogue form
129
How a speaker converts electric current to sound
Current flows through the coil of wire wrapped around an iron core, causing the core to become a temporary electromagnet. As the current varies, the induced magnetic field in the core varies causing it to be attracted to the permanent magnet and vibrate. The iron core is attached to a cone made of paper or thin magnetic materials which vibrates along with it to produce sound waves
130
Types of memory and storage devices (2)
Primary memory
Secondary storage
131
Primary memory vs secondary storage (2 for primary, 4 for secondary)
Primary:
-Directly addressable by CPU
-Contains RAM ROM and cache memory
Secondary:
-Not directly addressable by CPU
-Contains all non-volatile devices
-Can be external or internal to the computer (more permanent data storage)
-HDD,SSD,DVD, memory stick and Bluetooth-ray disk
132
Features of RAM (3)
Used to store data
Volatile (memory contents lost when powering off the computer
Used to store things currently in use
133
Why does increasing RAM allow a computer to operate more quickly
As the RAM becomes full, the CPU has to constantly access the secondary data storage devices to overwrite old data on RAM with new data. Increasing RAM size reduces the number of times this has to be done allowing the computer to operate more quickly
134
Types of RAM technology (2)
Dynamic RAM (DRAM)
Static RAM (SRAM)
135
Input device
converts inputs into digital data which can be processed
136
Output device
shows the results of the processing in a way humans can understand
137
Pressure sensor
A transducer that generates different electric currents as pressure is applied
138
Acoustic sensor
Microphones that convert detected sound into electric signals/pulses
139
Moisture sensor
Measures water levels in eg. Soil based on the electrical resistance of the sample being monitored. Moisture levels in a green house
140
Humidity sensor
Measures the amount of water vapour in a sample of air based on the fact that the conductivity will change based on the amount of water present
141
Light sensor
Uses photoelectric cells that produce an output in the form of a current depending on the brightness of the light
142
Transducer
Converts energy from one form to another
143
Accelerometer
Measure acceleration + motion of an application. A piezoelectric cell is used whose output varies according to the change in velocity (applies airbags in a crash)
144
Level sensor
Use ultrasonics or conductivity to monitor liquid levels, can be optical or mechanical in nature
145
Purpose of RAM
To store current data and program instructions in use
146
Purpose of ROM
To store the computer's boot-up sequence as it is non-volatile
147
Why a computer needs RAM and ROM
ROM initiates the boot process and loads firmware instructions. RAM stores the operating system and in-use applications & data. Processing is done with data from RAM.
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What is meant by primary storage
a key component of a computer system, directly addressable by the CPU, that enables the system to function. Primary storage includes random access memory (RAM), read only memory (ROM), cache and flash memory.
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Features of DRAM (6)
Needs to be constantly refreshed
Less expensive to manufacture than SRAM
Higher memory capacity than SRAM
Main memory is constructed from DRAM
Consumes less power than SRAM
Consists of a number of transistors and capacitors
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Features of SRAM (4)
Uses flip-flops to hold each bit of memory
Doesn’t need to be constantly refreshed
Has a faster data access time than DRAM
CPU memory cache makes use of SRAM
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Flip flop
Electronic circuit with only 2 stable conditions
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Latency
Lag in a system eg. Time it takes to find a track pm a hard disk (depends on the time it takes to rotate around to its read/write head
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SSD endurance
Total guaranteed number of times data can be written to or read from a solid state drive in its usable life cycal
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Features of RAM (5)
Volatile
Temporary memory device
can be written to and read from
Used to store data files, part of the OS, files etc currently in use
Can be increased in size to improve operational speed of a computer
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Features of ROM (4)
Always used to store BIOS and other start up data
Non-volatile
Permanent memory device
Data stored cannot be altered
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Categories of secondary storage (3)
Magnetic
Optical
Solid state
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Magnetic storage
HDD
Data is stored in a digital format in sectors (contains a fixed number of bytes) and tracks on the 2 magnetic surfaces of the disks/platters made of aluminium, glass or ceramic material, the drive will have a number of platters that can spin about 700 times a second. Read write heads consisting of electromagnets, that can move from the centre of the disk and back 50 times a second can access all of the surfaces of the platters. Latency plays a role. All data will be read sequentially
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Page
Fixed length consecutive block of data utilised in virtual memory systems
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Paging
Used by memory management to store and retrieve data from HDD/SSD and copy it into RAM
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Removable hard disk drives
HDD’s external to the computer that can be connected using USB ports. Thus a way of backing up files or transferring them between computers
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Solid state drives
Have no moving parts and all data is retrieved at the same rate. Data is stored by controlling the movement of electrons within NAND or NOR chips. Data is stored as 0 and 1 in millions of tiny transistors (one a control, one a floating gate) within the chip to produce non-volatile rewritable memory
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Benefits of SSD over HDD (7)
More reliable (no moving parts)
Lighter
Don’t have to get up to speed before they work properly
Lower power consumption
Run cooler than HDD’s
Very thin (no moving parts)
Data access is faster
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Floating gate and control gate transistors
Use CMOS (complementary metal oxide semi-conductor) NAND technology. Flash memories make use of a matrix, at each intersection on the matrix’s there is a floating and controlled gate. Control gate lies on top, then a dielectric coating (insulation) separates it from the floating gate which allows the floating gate transistor to retain its charge of 1 (keeping the memory non-volatile).
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Why should a SSD be used at least once a year
So that the charge doesn’t leak away.
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How to program an intersection cell (floating and controlled gate transistors)
Apply a voltage to the control gate, electrons from the electron source are attracted to it but become trapped in the floating gate due to the dielectric coating, giving us control over the bit value stored at the intersection
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How an intersection on a matrix is arranged
Control gate
Dielectric coating
Floating gate
Tunnel oxide coating (allows electrons through)
Electron source
Substrate
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Main drawback of SSD (2)
Longetivity - only 20GB of write operations per day over a 3 year period (SSD endurance) so it cannot be used in servers where a huge number of write operations take place every day.
Not possible to over-write existing data, you have to erase the old data then write the new data at the same location
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Example of SSD technology
Memory stick/flash memories/pen drives
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Memory sticks/flash memories
Use solid state technology and connect to the computer via USB port, small and lightweight, used as a small back up device and for transferring files between computers. Used as a dongle (containing additional files to run software) in complex + expensive software to prevent copying + unauthorised access.
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Optical media (2)
CDs + DVDs
Blu-ray disks
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CDs + DVDs
How they work
Optical storage devices, a laser is used to read +write data from the pits and lands on the surface of the disk.
Thin layer of metal alloy or light sensitive organic dye stores the data. A single spiral track is followed by the red laser from the centre outwards as the disk spins and the optical head moves to the point where the laser beam contacts the disk surface. Divided into sectors allowing direct access to data. Outer part of the disk runs ter than the inner.
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How does wavelength of a laser light effect the capacity of a medium
The shorter the wavelength, the greater the storage capacity
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How can CD’s and DVDs be designated (2)
R (write once only)
RW (can be written to or read from many times)
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Differences between DVDs and CDs
DVDs have the opportunity for dual layering (increased storage capacity) - 2 layers of DVD joined with a transparent spacer + a very thin reflector. Second laser focuses at a fraction of a millimetre difference to the first.
DVD’s use lasers with a wavelength of 650 nanometres, CDs use 780 nanometres
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Most common use of DVD and blu-ray
Why not CD
Supply of movies and games
Memory capacity of CD isn’t big enough
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Main differences between DVD and blu-ray (4)
Blue laser used instead of red
Blue laser allows pits and lands to be smaller giving 5x the storage space
Automatically come with a secure encryption system (prevents piracy+copyright infringement)
Data Transfer rate of blu-ray is 36Mbps (26 higher than DVD)
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Interactivity blu-ray allows (6)
Record high definition TV programs
Skip quickly to any part of the disk
Create playlist of recorded movies + TV programs
Edit/reorder recorded programs on the disk
Automatically search for empty space on the disk
Accès websites and download subtitles
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Capacity of blu-ray vs DVD (3)
Dual layer DVD can store 4.7GB (2 hour standard def. movie)
Single layer blu-ray can store 27 GB (2 hour high def/13 hour standard def)
Dual layer blu-ray can store 50GB (4.5 hour high def/20 hour standard def)
