CHAP 1: Data representation Denary - base 10, 0-9, used by humans Hexadecimal - base 16, 0-9 and a-f, used by programmers Binary - base 2, used by computers To convert hexadecimal to denary; 1) conv to binary 2) conv binary to denary Uses of hexadecimal system 1) 2) 3) 4) Error codes IPV6 address MAC address HTML colour codes Error codes - Refers to memory location of where error occurred IPv6 ( internet protocol) - A 128 bit (32 hex) number broken into 16 bit chunks - Uses : to separate bits MAC address (media access control) - Refers to a number that identifies a device on the internet - Made of 48 bits - 6 groups of hexa digits NN:NN:NN:DD:DD:DD HTML colour codes (hypertext mark-up language) - Not a programming language - Used to develop/ design web pages #FF 00 00 #00 FF 00 #00 00 FF #FF FF FF white #00 00 00 black Representation of text and sound - Character sets: set of characters recognized by a variety of systems ASCII UNICODE Sound representation - Analogue signal → digital signal using ADC ADC is capable of taking multiple samples per second (sample rate) Sample rate: number of wavelengths samples per second ➔ Determines quality of audio Bit depth/ sample resolution: number of bits used to store each sample Advantages of high sampling resolution ➔ Larger dynamic range ➔ Better sound quality ➔ Less sound distortion Disadvantages ➔ Big file size ➔ Takes longer to download/ transmit ➔ Requires greater processing power Image representation - Image: grid of pixels Image w matrix of pixels: bitmap image Each pixel is represented by a binary number Image resolution: number of pixels in an image Colour depth: number of bits used to represent each colour ➔ 8 bit colour depth: 256 shades Advantages of high image resolution ➔ Better image quality ➔ Better colour Disadvantages ➔ Big file size ➔ Takes longer to download/ transmit ➔ Impacts no. of images that can be stores Data compression - Transmit files using lower bandwidth (transmission capacity of a computer network) To save storage Reduce time taken to download/ transmit file/ stream audio file Reduce cost of cloud storage Lossy compression - Eliminate unnecessary data. Original file cannot be reconstructed Details will be lost compared to original file Jpeg (joint photographic expert group) ➔ Reduces colour depth MP3 / MP4 (motion photographic expert group) ➔ Perceptual music shaping - two overlapping sounds; removes softer sounds ➔ Removes sounds outside of human hearing range Lossless compression - Data can be reconstructed after compression Used when data loss is disastrous RLE (run length encoding) ➔ Reduces size of long string of identical data Data transmission Data packets - Data is broken up into packets and transmitted using different routes Yay : good when a route is busy Boo : 1) packets need to be reassembled at destination 2) might get lost during transmission Packet structure Header - Ip address of receiver and sender - sequence no. of packet - size of packet payload trailer - data - method of identifying end of packet - CRC error detection CRC (cycle redundancy check) 1) Sender’s computer will calculate all the number of 1’s in the payload and store it as a hex value 2) Receiver computer will recalculate and compare with hex number sent 3) If different, packets will be need to resent Packet switching - Packets taking different routes to reach its destination Routes taken depends on router When packets arrive, they need to be reassembled using the identification data from the header and trailer Trailer is checked w parity (number of 1’s) Advantages ➔ Possible to overcome busy/ faulty routes ➔ High data transmission ➔ Easy to expand package usage ➔ No need to tie up single communication line Disadvantages ➔ Might get lost during transmission ➔ Have errors w real time streaming ➔ Delay at destination while being reassembled - Packets might get lost during transmission due to bouncing from one router to another, which might cause the network to freeze Router hopping is implemented to overcome this Hop number is placed at header of each packet, everytime it bounces off a router, hop number reduces by one If hop number reaches 0, packet will be resent Transmission methods Simplex half duplex full duplex Transmission types Serial - data transmitted one bit at a time over a single wire parallel - data transmitted multiple bits at a time over multiple wires Advantages - more accurate - works well over long distance - data is fully synchronised Advantage - fast - works well over short distance Disadvantage - slow Disadvantage - data can arrive skewed - longer wire, higher chances of errors USB (universal serial bus) - Serial data transmission Most common input/output port on computers Half duplex/ full duplex Plugging usb device into comp: 1) Comp automatically detects the device 2) If device recognised, device driver will load up allowing device n comp to communicate 3) If unrecognised, appropriate device driver will be downloaded Advantages - automatically detects device - backwards compatible - most devices use USB - easy to add more USB hubs - supports diff transmission rates Disadvantage - max cable length of 5 m - earlier versions of USB may not be supported by latest computers - slow transmission rates (compared to ethernet connections) USB-C - 24 pin symmetrical connecter Small n thinner compared to USB 20v power connectivity: full sized devices can carry data n charge at 10 gb/s Expected to be new industry standard Error detection Errors occur due to ➔ Interference ➔ Problems during packet switching ➔ Skewing of data 1) parity check 2) checksum 3) echo check 4) ARQ: automatic repeat request 5) check digit Parity check - Parity: number of 1’s in a bit Can either be odd/even 1) agreement between sender/receiver is made if parity is odd/even 2) when receiver receives data, parity will be calculated; if meets protocol = no errors Limitations: ➔ Exact location of error cant be detected if only one bit is transmitted ➔ Error cannot be detected if an even number of bits is changed → parity blocks used to overcome this Checksum - Data sent in blocks along w an additional value (checksum) at the end of the block 1) checksum value calculated from a block of data b4 transmission 2) calculation is done by an agreed algorithm, 3) checksum value sent w block of data 4) once received, checksum value is recalculated and compared 5) if the value is the same, no errors. Otherwise, request will be sent out to resend data Echo check - Data is sent to another device, copy of same data would be resent to compare Not reliable. Errors could happen at any stage ARQ 1) sender sends data w an error checking code at end of data 2) code is used to see if any errors occurred 3) if no errors, acknowledgement will be sent → a message to indicate that data is received → either pos/ neg (error) 4) a time out is used by sender device → a predetermined amount of time to wait for an acknowledgment 5) if no acknowledgment is sent during the time out period, data will automatically be resent until pos acknowledgment is received Check digit (data entry error detections) - Final digit included in a code. Calculated from all the other digits in a code Used in ISBN, VIN Can detect: → phonetic errors → omitted numbers → transposition errors → incorrect digit entered Encryption - Representing data using different characters Used to protect data from hackers → doesn't prevent hacking; makes data useless 1) symmetric - Uses 1 key to encrypt and decrypt - Key interception problem 2) asymmetric - Uses 2 keys. Public and private 1) Receiver makes public key and private key. Keys are mathematically linked but cannot be derived from one another 2) Receiver sends public key to sender 3) S uses public key to encrypt 4) R uses private key to decrypt CHAP 3: HARDWARE COMPUTER ARCHITECTURE ➔ ➔ ➔ ➔ ➔ ➔ ➔ CPU Von neumann architecture ALU, CU and registers Control, address and data bus Cores, cache and internal clock Fetch, Decode, Execute cycle Embedded systems - A comp is made of external and internal components Basic principles across all devices are the same 1) CPU: central processing unit - Known as microprocessor Central to all modern computers Installed as an integrated circuit on a single microchip Responsible for all operations in a computer Cpu consists of: ➔ CU (control unit) ➔ ALU ( arithmetic and logic unit) ➔ Registers and busses ➔ System clock 2) von neumann architecture ➔ ➔ ➔ ➔ To store programs and data in a memory CPU Can access memory directly Comp to store programs n data Stored programs were made of instructions which could be executed in sequential order ALU - Allows required arithmetics (+ - nd shift) or logic (AND, OR, NOT) operations Results of these operations is stored in accumulator CU - Reads instruction from memory and writes in memory using buses Coordinates all operations during executing instructions REGISTERS - Fast access memory that holds data and instructions during manipulation REGISTER SHORT FORM USAGE Current instruction register CIR Stores current information Accumulator ACC Stores results of ALU operations Memory address register MAR Stores address of memory location currently being read/written Memory data register MDR Stores data of memory location currently being read/written Program counter PC Stores address of next location System bus To connect cpu to memory and input/output address ADDRESS BUS (unidirectional) Carries signals relating to addresses between processor to memory CONTROL BUS (unidirectional) Carries control signal (read/write) and coordinates all activities within a computer. From processor to memory DATA BUS (bi-directional) Sends data between processor, memory and input/output device ⭐ READ OPERATION 1) Address of location will be in MAR 2) Read signal sent by CU is sent to memory unit via control bus 3) Content of memory location is stored in MDR ⭐ WRITE OPERATION 1) New value stored in MDR 2) Address of location stored in MAR 3) Write signal sent by CU is sent to memory via control bus 3) fetch, execute, decode - To carry out instructions, data needs to be fetched and stored in suitable registers 1) CPU fetches instructions from memory and is stored in registers 2) Address bus is used to store location and data bus is used to store instructions 3) Decodes in binary then will be executed FETCH 1) address of next location will be stored in PC 2) address is copied to MAR 3) instructions from MAR will be copied into MDR 4) instructions from MDR will be stored in CIR 5) PC will increase by 1 6) instructions will be decoded by CU 7) instructions will be executed by ALU 8) results of ALU will be stored in ACC 4) factors of cpu performance ➔ System clock ➔ Cache ➔ Cpu cores System clock - Small quartz circuit that generates electrical impulses in CPU - Controls timing of all computer operations - Part of system clock is called clock speed, measured by pulses per second - 1 gigahertz = 1b electrical impulses - Faster clock, more instructions could be executed Cache - Modern CPU chips have built in mini RAM’s called cache memory - Used where a processor has instructions and data it needs regularly → used when fast data access is needed - When CPU reads memory, it checks cache first then RAM - The bigger the cache, the less time it takes for a processor to fetch instructions CPU cores - CU + ALU + REGISTER = processing core - More core = more execution of instructions at the same time - BUT more cores = reduce overall performance → more cores need to communicate w CPU Buses width - Larger bus = more instructions/data carried Overclocking - High clock speed = data fetching: faster than original clock speed → cpu unable to execute instruction before next instruction arrives → crashing, overheating = unreliable performance 5) instruction sets - Set of common instructions → set of operations decoded in sequence - Instruction is made of OPCODE and OPERAND OPCODE OPERAND → short for operation code → data required for specific job as detailed by OPCODE → informs CPU what to do → may be piece of data or address location within RAM or register → stored on hard disk n copied to RAM when comp is powered on → most used OPCODE will be in cache instead of RAM 6) embedded systems - Combination of hardware and software that’s designs to carry out specific set of functions → hardware: electrical/ electro-mechanical/ electronic MICROCONTROLLERS MICROPROCESSOR SoC (system on chip) CPU,RAM,ROM + other peripherals embedded onto one chip to carry out a specific task Integrated circuit w cpu microcontroller (cpu, memory, input/output ports and secondary storage on a single microchip) Embedded systems are either ➔ Programmable ➔ Can be updated ➔ w wifi (automatic) ➔ Connect to PC and download update to software ➔ Non programmable ➔ Cant be updated Advantages - small n easy to carry - cheap - consume little power disadvantages - any device that can be accessed over the internet can be hacked n can get virus - usually thrown away due to difficulty in updating - troubleshooting faults in device becomes specialty task INPUT DEVICES 1) Barcode scanners - A series of dark and light parallel lines with varying thickness 1) 2) 3) 4) Barcode is read with red laser Dark lines absorb light, light lines reflect line Reflected light is read by sensor (photoelectric cells) Pattern is generated which is converted into digital data → computer can understand barcode 5) Barcode will be represented as WBBW (0110) 6) Barcode number searched in database 7) When found, stock item details will be displayed 8) Number of stock will reduce by 1 every time a barcode is scanned 9) When no of stock reaches re-order level, more items will be automatically ordered 10) When new stock items arrive, database will be updated advantages (for management) - easier + faster to change prices - more up to date info abt stock - allows for auto stock control advantages (for customers) - accurate - itemised receipt made - short que lines 2) QR (quick response) scanners - Matrix of dark squares against light bg Holds over 7000 digits Three large squares at corners of code acts as alignment Remaining small corner is to ensure right size n angle of camera is used when qr is scanned ➔ Advertise products ➔ Auto access to online websites ➔ Stores boarding passes Advantages Disadvantages Can hold a lot of info Each tiny square holds data, if one is scratched, the qr code cannot be read Fewer errors Sometimes required to install external app to read qr Easy to read Can be used to transmit malicious code Easy to transmit/share images Can be encrypted 3) microphones - Built in or external device When mic picks up sound, a diaphragm produces an electrical current. Currents gets picked up by sound card which has ADC and converts it into digital values and stored in a computer 4) mouse - To select times Optical - used red LED to detect movement mechanical - uses a ball at the bottom of the mouse to detect movement Optical over mechanical ➔ Lighter ➔ No moving parts ➔ Can work on any surfaces ➔ Isn't affected by dust Wired over wireless ➔ Cheaper ➔ No signal lost ➔ No need to dispose batteries 5) scanners - 2d n 3d Convs hardcopy → hardcopy 2d scanners Measures width n length 1) 2) 3) 4) 5) Open cover, place doc, close cover Bright light illuminates n scans doc Scan head moves across doc till whole page is scanned CCD (character couple device) takes scanned image n convs it into softcopy Editing softcopy uses OCR (optical character recognition). Convs doc into text file format Uses of 2d scanners ➔ Read passports ➔ OCR used to change text in electrical form ➔ Allows user to input data into existing database 3d scanners - x, y, z coordinates - Images scanned can be used in CAD (computerised aided design) 1) 2) 3) 4) 5) CT (computed tomographic) scanners are used to create 3D images CT scanners build up image using a series of thin slices Each slices is built using x-rays, radio frequency or gamma imaging Each slice is stored as digital image in comp memory Whole object is represented digitally in comp memory 6) digital cameras - Controlled by an embedded system which carries out these tasks ➔ Adjust shutter speed ➔ Focus image automatically ➔ Operate flash automatically ➔ Adjust image size ➔ Remove ‘red eye’ when flash is used 1) Image captured when light passes through lens onto light sensitive cell 2) Cells is made up of millions of tiny sensors called CCD which convs light into electricity 3) Image is the conv to a digital form using ADC 7) keyboards - Input device for data entry Each character on keyboard has an ASCII value Each character pressed is converted into a digital signal a computer interprets 8) touch screen - Capacitive Resistive Infra red capacitive - Two layers of glass protective layer, conductive, glass substrate - Layers acts as a capacitor that creates an electric field between glass plates - Human skin conductor of electricity → bare finger touches skin → electric field of conductive layer changes - Installed microprocessor calculates locations where E.F changed Surface Projective Sensors + voltages placed at corners to create electric field Transparent conductive layer in the form of XY matrix - creates 3d electric field Finger touching screen will draw current from each corner Works w bare fingers, stylus, thin surgical gloves or cotton gloves Only works w finger Allows multi touch facility YAY! - good visibility in sunlight - durable - Allows multi touch facility (projective) NAY :( - expensive - sensitive to electromagnetic radiation - surface screen only works w bare fingers infrared - Uses glass screen w an array of sensors and infrared transmitters - Sensors detect infrared radiation YAY! - allows multi touch facility - isnt affected by scratches or cracked screen - good screen durability NAY :( - sensitive to light - sensitive to moisture - possible for accidental activation Resistive - Made of two layers of electrically resistive material w voltage applied - Upper layer is made of flexible polyethylene w resistive coating - Bottom layer is made of glass w resistive coating YAY! - durable - not affected to moisture NAY :( - low screen durability - low touch sensitivity 9) sensor - Sensor pick up signal → ADC → microprocessor compares data with stored value → DAC → signal sent to actuator → action taken OUTPUT DEVICES 1) light projectors Dlp: display light projector - Uses micro mirrors on small DMD chip (digital micromirror device) - Number and arrangement of DMD determines resolution of projection - Micro mirrors tilt towards light → on - Micro mirrors can switch on/off thousands of times per second and create around 1024 shades of grey 1) 2) 3) 4) 5) Bright light passes through colour filter otw to DMD White light split into 3 primary colours Shaping lens mixes colours into secondary colours DMD will create 1024 shades of each colour Lens will project produced coloured image LCD: liquid crystal display - Old 1) White beam generated from bulb/ LED inside the projector body 2) Beam of light sent to group of monochromatic coated mirrors; reflects light at different wavelengths (RGB) 3) Three diff colours pass through three LCD screens 4) Three vers of images produced 5) Image recombined to produce full image 6) Image passes through projector lens onto screen DLP YAY! NAY :( High contrast ratios Moving image tends to suffer from ‘shadows’ Higher reliability Do not have grey components in image Uses single DMD chip Colour definition is not good as LCD Quiet Smaller and lighter LCD YAY! NAY Sharp images Bad contrast ratios Better colour saturation Limited life More efficient in energy use LCD panels degrade
