Hardware and Communications
- Created by: Schofe98
- Created on: 01-06-17 15:20
Components of a Processor
Arithmetic Logic Unit - repsonsbile for all calculations and logic operations.
- can act as a conduct for input and output to and from the processor
Control Unit - manages the execution of machine code by sending control signals
Registers - small blakc of memory which is used as temporary storage for instructions as they are being processed.
- program counter
- memory address register
- memroy data register
- current instruction register
- Accumulator
Components of a Processor
Arithmetic Logic Unit - repsonsbile for all calculations and logic operations.
- can act as a conduct for input and output to and from the processor
Control Unit - manages the execution of machine code by sending control signals
Registers - small blakc of memory which is used as temporary storage for instructions as they are being processed.
- program counter
- memory address register
- memroy data register
- current instruction register
- Accumulator
Registers
Program Counter - stores the address for the next instruction to be executed
Memory Address - contains the address of the instruction or data to be fetched next
Memory Data - contains the data or instruction that has been fetched.
Current instuction register - holds a copy of the instruction that has been fetched for executing
Accumulator - any instruction that performs a calculation make use of this.
Memory and Caching
L1 - extremely fast but relatively small.
usually embedded within the Central processing unit.
L2 - often has a higher capacity than L1 and as a result operates slower
Maybe located on the CPU, dedicated to single or pairs of cores, or located on a seperate chip to avoid becing slowed by traffic of main buses.
L3 - works to improve the performance of L1 and L2 cache.
Parallel Processing
Two or more processors work together to perform a single task
- the task is split into subtasks (threads) which are executed simultaneously by available processors.
Advantages:
- More instructions can be processed in a shorter time because they are being executed simultaneously.
- Tasks can be shared to reduce load on individual processors and avoid bottlenecks.
Disadvantages:
- difficult to write programs for multi core programs
- results from different processors need to be combined at the end of processing, which can be complex and adds time.
- not all tasks can be split acorss multiple processors
- concurrency introduces new classes of software bugs.
FETCH - DECODE - EXECUTE
Single processor can only execute a single instruction at a time.
1. Fetch - fetches the data and instructions from main memory then stores them in its own internal registers.
2. Decode - the CPU 'understands' the commands within the instructions using an instruction set.
3. Execute - data processing and then stores in another register.
Once finished one cycle, the CPU will start the next cycle.
Memory and Caching
Input and Output Devices
Optical character recognition – converts printed media into editable text documents using a scanner.
- OCR is a post processing step that performs pattern matching by scanning the image for shapes that it can recognise as letters, numbers and symbols.
- Easy for humans to read, but complicated for the computer
Optical mark recognition – A reader reads forms to detect black lines and marks and note the position on the page.
- Used in predefined forms
- Multiple choice exam and registers, as they can be automatically marked and processed.
- Not suitable for written communication
Magnetic ink recognition – combination of ink containing iron oxide and specific fonts so it can read by a MICR reader.
- Normally just used in cheques.
- Doesn't have to rely on OCR which can be problematic.
Touch screens - resisitive and capacitive, both versions send X and Y coordinates of the touch when touch is registered.
- Resistive touch screens are much cheaper and are made up of two transparent sheets which send a voltage when they touch.
- Capacitive allow for much sharper image and for multiple touch points to be recorded simultaneously and making them more expensive.
Secondary Storage
Magnetic storage devices - a hard drives is a high capacity stoage meduim.
- has a fast transfer rate and access time
- provide a good compromise between stoage capacity, performance and cost.
- hard drives stores data on a hard drive plater; data is read and saved using an arm that has a special read/write head.
Flash storage - Solid state drives are becoming more popular as they tend to have a better performance than hard drives
- Tend to be more expensive
- No spinning disk or moving read head
Optical drives – using lasers to store data by burning microscopic indentions into a disk such as a CD.
- On DVDs data is stored on two levels and there are two lasers on different wave lengths used to read the data.
Fragmentation and Defragmentation
Files become fragmentated meaning they are split and stored on different parts of the disk.
- Takes a lot longer to collect data which is widely fragmented
Defragmentation is the process where files are physically re-arranged so that they are no longer fragmented and parts are stored together.
- Improves the speed of accessing data
Networks
Networking standards are what underpin communications.
A distibution system is where comptuers work together by sharing services with one another to provide a complete system.
- The internet is a worldwide communications intfrastructure, which means that you can access websites in any country in the world.
Client server - services are made available on servers to which clients connect in order to access the services eg Web Servers.
Peer to peer - each computer has the same status as the others.
- No computer acts as a server, meaning that peers must work togerther to fulfil the required task eg file sharing.
- Allows very large files to be downloaded efficiently without need for a powerful server.
Protocols
A set of rules that governs communications. A number of protocols together make a protocol stack.
HTTP: allows resources to be transmitted over the network.
FTP: works on an interactive model and is used when copying (uploading or downloading) a file from one location to another via the internet.
SMTP: standard internet for electronic mail transmission.
TCP: (transmission control protocol) provides relaiable and error checking streams of packets over a network and is the core transport protocol for HTTP.
IP address: each computer must have an unique address to the data is sent to the correct machine over the internet.
Networking
Hand shaking - to set up a communication link, both devices need to agree on a set of protocols to use.
- Signal from one device to the other and is ackowledged by the second.
Router - routes the packets to the correct port.
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