1. data storage
1.1. hard disk drives
1.1.1. where data is stored and retrieved using magnetic properties
1.1.2. stores operating system and installs programs/users data
1.2. solid state drives
1.2.1. reduced latency when compared to hard disk drives
1.2.2. data is stored and retrieved using electronic properties of NAND chips
1.3. optical storage systems
1.3.1. surface of these devices are made of light sensitive organic dyes or metal alloys
1.3.2. data is stored and retrieved using optics
1.4. parameters used to choose storage device
1.4.1. speed
1.4.2. capacity
1.4.3. portability
1.4.4. durability
1.4.5. reliability
1.5. memory access
1.5.1. direct memory access
1.5.1.1. any storage location can be accessed at any moment
1.5.2. sequential memory access
1.5.2.1. allows the user to access data one by one in a sequence
2. Input and Output devices
2.1. Input devices
2.1.1. Scanner
2.1.1.1. 2d scanner
2.1.1.1.1. panel is raised and document is placed on the glass. cover is then closed and a bright light illuminates the document
2.1.1.1.2. scan head moves across the document until the whole page has been scanned
2.1.1.1.3. image is focused and falls on a CCD and is then converted to electric form
2.1.1.2. 3d scanner
2.1.1.2.1. scans solid objects and a 3 dimensional image representing the object is used
2.1.1.2.2. several images at various 3d coordinates of the object are taken by the scanner
2.1.2. barcode reader
2.1.2.1. barcode: a series of dark and light parallels of different thickness
2.1.2.2. the barcode is read by a red LED or laser
2.1.2.3. light from the white areas is reflected back off the barcode
2.1.2.4. pattern is generated and converted to digital data
2.1.2.5. identifies object and its price
2.1.3. qr code reader
2.1.3.1. scans using phone's camera
2.1.3.2. qr code is analysed using internet connectivity and phone number appears on the screen
2.1.4. digital camera
2.1.4.1. have a microprocessor which automatically adjusts the shutter speed, focuses the image, operates the flash,...
2.1.5. keyboard
2.1.5.1. each key on the keyboard as a unique ASCII code
2.1.5.2. when a key is pressed, it is converted into a digital signal which the computer interprets
2.1.6. pointing devices
2.1.6.1. requires a flat, non-reflective surface.
2.1.6.2. uses a red light to detect motion in the 2d coordinates
2.1.7. microphone
2.1.7.1. has a diaphragm that vibrates to produce electrical signal
2.1.7.2. signal is sent to sound card which is converted to binary values
2.1.8. touchscreen
2.1.8.1. capacitive
2.1.8.2. infrared
2.1.8.3. resistive
2.1.9. sensor
2.1.9.1. temperature
2.1.9.2. pressure
2.1.9.3. light
2.1.9.4. motion
2.1.9.5. sounds
2.2. output devices
2.2.1. printers
2.2.1.1. inkjet
2.2.1.2. laser printers
2.2.1.2.1. uses dry powder rather than liquid ink
2.2.1.3. 3d printers
2.2.2. loudspeakers/headphones
2.2.2.1. digital data stored in the computer is converted to analogue data
2.2.2.2. sound wave is passed through the amplifier
2.2.2.3. sound emerges out of speaker
2.2.3. LCD + LED monitors
2.2.3.1. LED
2.2.3.2. LCD
3. network hardware
3.1. routers
3.1.1. forwards data packets until it reaches its destination
3.1.2. decides the path in which the data packet has to be sent
3.2. modems
3.2.1. turns digital data into an electrical signal
3.3. hubs
3.3.1. broadcast data from a device to all devices on its network
3.3.2. can result in unnecessary data transfers
3.4. switches
3.4.1. switches the MAC address of devices
3.4.2. filters data packets according to MAC address and forwards it to specific device
3.5. bridges
3.5.1. connects 2 separate LAN networks
3.6. wireless access points
3.6.1. built into routers
3.6.2. how wireless devices connect to wireless networks
4. CPU
4.1. responsible for processing the instructions given to a computer
4.2. contains ALU, Control Unit and Cache memory
4.3. performance is affected by:
4.3.1. cores
4.3.1.1. a processing unit
4.3.1.2. consists of ALU and CU registers
4.3.2. clock rate
4.3.2.1. indicates the number of instructions processed by a CPU in a second
4.3.2.2. measured in MHz or GHz
4.3.2.3. over-clocking: increasing the speed of the computer by increasing the CPU clock
4.3.2.4. if computer is forced to work at a speed higher than its limit, instructions might not execute completely --> overheating
4.3.3. cache
4.3.3.1. cache size
4.3.3.1.1. small memory part located close to CPU, holds the data and instruction that the CPU is likely to use more frequently
4.3.3.1.2. control unit reduces time by checking cache before requesting instructions from RAM or main memory
4.3.3.2. cache memory
4.3.3.2.1. increases CPU speed
4.3.3.2.2. faster to use compared to RAM
4.3.4. processor type
4.3.4.1. complex instruction set computing (CISC)
4.3.4.2. reduced instruction set computing (RISC)
5. Parts of the Von Neumann System
5.1. Buses
5.1.1. Adress bus
5.1.1.1. transmit the address between processor and memory
5.1.1.2. unidirectional: sends from the processor to memory and in/output devices
5.1.2. Data bus
5.1.2.1. sends data between the processor, memory and in/output devices
5.1.2.2. bi-directional
5.1.3. control bus:
5.1.3.1. signals sent by processor to control memory and peripheral devices
5.1.3.2. unidirectional
5.2. Memory Unit
5.2.1. consists of number partitions
5.2.2. each partition consists of data + an address which uniquely identify every location in memory
5.3. Read/Write operations
5.3.1. read
5.3.1.1. memory address register and memory data registers are used to read content.
5.3.1.2. read signals is sent by the processor to memory and are then copied to MDR
5.3.2. write
5.3.2.1. data is written into MDR
5.3.2.2. address is copied into MAR register
5.3.2.3. "write signal" is sent by processor to memory unit using control bus and then the location is written with the data in the MDE
5.4. Processors
5.4.1. ALU
5.4.1.1. Processor contains arithmetic logic unit and control unit
5.4.2. CU
5.4.2.1. controls memory and contains CIR (current instruction register) and program counter (PC)
5.4.2.1.1. CIR
5.4.2.1.2. PC
5.4.2.2. control unit reads instructions from memory, decode sit and sends control signals to the memory to carry out the instruction
5.5. FDE cycle
5.5.1. fetch
5.5.1.1. instruction is fetched from memory and then copied to MDR
5.5.1.2. MDR contents are copied to CIR and instructions are processed
5.5.2. decode
5.5.2.1. instructions are decoded so it can be executed
5.5.3. execute
5.5.3.1. processor sends control signals to memory unit and devices in computer system act accordingly
6. computer memory
6.1. primary memory
6.1.1. memory that is directly accessed by CPU
6.1.1.1. registers
6.1.1.2. cache
6.1.1.3. ram
6.1.1.3.1. a temporary memory which stores data, files and parts of the operating system (that is currently in use)
6.1.1.3.2. types of ram:
6.1.1.4. rom
6.1.1.4.1. permanent memory that is used to store instructions that are executed when the computer is on
6.1.1.5. virtual memory
6.1.1.5.1. the part of the hard drives that stores data when the computer has too many processes and programs running at the same time
6.1.1.5.2. used when RAM does not have enough capacity
6.1.2. latency: the time taken by components to respond to a request
7. networking
7.1. data packets
7.1.1. when data is broken into small chunks when sent over a network
7.2. types of networks
7.2.1. LAN (local area network)
7.2.1.1. a network of computers within the same building
7.2.1.2. do not need to connected to the internet
7.2.1.3. example: connections of computers in an office
7.2.2. WAN (wide area network)
7.2.2.1. a network of LANS in a geographical area
7.2.2.2. example: the internet
7.2.3. PAN (personal area network)
7.2.3.1. connects personal connections in a home
7.2.3.2. wired
7.2.4. WPAN (wireless personal area network)
7.2.4.1. short distance wireless networks
7.2.4.2. example: bluetooth connection within devices in a car
7.2.5. MAN (metropolitan area network)
7.2.5.1. connects devices in a city
7.2.6. SAN (storage area network)
7.2.6.1. provides servers that enable users to store files in a large scale
7.2.7. VPN (virtual private network)
7.2.7.1. a network that creates safe and secure connection for an organisation over the internet
7.3. network models
7.3.1. client - server models
7.3.1.1. clients:
7.3.1.1.1. computers that request information
7.3.1.2. servers:
7.3.1.2.1. computers that provide information
7.3.1.3. examples:
7.3.1.3.1. web servers
7.3.1.3.2. application servers
7.3.1.3.3. print and mail servers
7.3.2. peer to peer models
7.3.2.1. each computer is responsible for providing data equally
7.4. types of connections
7.4.1. wired
7.4.1.1. copper cable
7.4.1.1.1. coaxial
7.4.1.1.2. unshielded and twisted
7.4.1.1.3. shielded and twisted
7.4.1.1.4. advantages vs disadvantages
7.4.1.2. fibre optic cables
7.4.1.2.1. made of glass
7.4.1.2.2. digital data is transmitted in the form of light signals which are decoded at the receiver end.
7.4.1.2.3. advantages vs disadvantages:
7.4.2. wireless
7.4.2.1. needs to have a wireless network interface card (NIC)
7.4.2.2. uses radio signals to connect to computers within its range
7.4.2.3. advantages vs disadvantages
7.4.2.3.1. adv
7.4.2.3.2. dadv