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Computer System Reliability Disaster Recovery How reliable systems are – Planning what to do if there Unreliable systems may have is a disaster (fire, flood, Anything that has a input, legal impact, aircraft natural disaster etc.). Making output device, processor and accidents etc., loss of data, sure you detect, correct and storage device loss of use of systems prevent problems by backups, spare hardware, impacting on business failover, backup power IPOS Down time When a computer system isn’t running, the system is down. It is important to reduce the amount the system is down especially when we rely on them so much De facto Open standards Failover Redundancy Standards that just develop by common use. They become the standard way of doing things (e.g. Programmers using Comments) Standards that are publically available. Software keeps an eye on the health of systems. If it detects a problem it may switch over to another working system (mirror system) and keeps the system running Keeping a spare piece(s) of hardware in case one breaks. Making sure there is no system down time (or very little) Open source software is publically available, experts can use and change. E.g. Android, Linux No one to blame if things g wrong CPU RAM ROM CACHE memory Processors instructions Volatile memory Non volatile Uses a fetch - decode – execute cycle Holds the most recent instructions that have been processed Holds the boot up program used when the computer first starts (boot strap) Volatile memory located as part of the CPU chip Lack of RAM is a likely cause of performance issues Generally holds less data than RAM. Manufacturing costs higher than RAM VIRTUAL memory Clock Speed Cores Flash Memory An area on the hard disk used as memory. Used when RAM is too small to deal with the amount of instructions. Effects the performance Speed of the processor. E.g. 4GHZ - this means the CPU can process 4 billion instructions per cycle/second Dual core – This means two Solid-state memory used as low cost secondary storage in portable devices and as removable memory Processing units in the CPU Quad core – four processing units per CPU For example USB, SD , Micro SD LOGIC GATE - AND LOGIC GATE - OR Both inputs need to be on (1) for the output to be on (1) One or the other inputs need to be on (1) for the output to be on (1) LOGIC GATE - NOT Truth Table The output is opposite to A table that contains all of the inputs and output the input combinations for a logic gate Hardware Software All the physical parts in a computer system Programs, apps e.g. motherboard, keyboard, mouse etc Software is the programs that run on a computer. File formats Instructions and Data When the CPU fetches data it will be treated as an instruction (something it has to do) or just data (information) INPUT devices OUTPUT devices Secondary Storage types Hardware that allows data to Hardware that allows data to be entered into a computer be output from a computer Magnetic – Hard disk system e.g. Keyboard, system e.g. monitor, printer Optical – CD,DVD, BlueRay mouse Solid state – No moving parts, USB, External hard disk Secondary Storage - Secondary Storage Secondary Storage Durability Portability Reliability How tough the storage is, how easy it is to damage How easy it is to move it. E.g. CD is easy to carry around, USB is lighter. Hard disk heavy and inside the computer Does the hardware work or does it break down easily? Can you reply on it? e.g CD can be scratched, Hard disk more durable Secondary Storage Non-volatile method for storing large amounts of data for long term use e.g. Hard disk, USB, SD card, Micro SD Used to store progams and data, other files Secondary Storage Sizes Magnet hard disks – large capacity, (GB/TB) Optical disks – (CD/DVD) holds large programs, videos, relatively slow but inexpensive 700mb (CD) 4,7GB(DVD) Flash (solid-state) – relatively inexpensive and good access times, can hold many GB of data Binary Units Binary to hexadecimal Split the binary into nibbles Binary to denary Hexadecimal to binary Denary to binary Binary addition (Overflow) Place a 1 under the correct numbers that add up to make the number When you add numbers together and the answer won’t fit into the number of binary digits (you need an extra binary digit) Hexadecimal Sound sampling Why do we use hexadecimal Storage sound numbers? Binary numbers Size file - interval get very big and difficult to use. It is easier for programmers to convert between binary and hex than binary and denary Character sets Metadata Resolution Colour depth A standard that converts all characters on a normal keyboard into binary codes for the computer to understand Information about the image that allows a computer to recreate the image from binary Describes the quality of an image. Measure in DPI (dots per inch)/pixels Refers to the number of bits used to represent the colour of each individual pixel Proprietary standards Industry standards UNICODE ASCII Standards owned by a company. For example products/software made by Microsoft way work in a specific way. This will be different to Apple products for example Mostly hardware standards that lots of companies agree to follow. For example USB An industry-standard character set that can represent thousands of different characters A relatively simple character set that can represent 128 different characters e.g. ASCII and UNICODE The higher the resolution the The more colours, the more e.g. the height, width, colour bigger the file size (and the bits needed so the larger the more space you need to save file size (and the more space depth it) you need to save it) Database – Validation The automatic checking of inputted data by a computer system to ensure it is sensible, no erroneous data is entered e.g. Range check –1-10 Presence check – “Required” Off the shelf software Relatively cheap, (compared to custom written software) Easily available from most computer shops Thoroughly tested so there won’t be any serious problems or bugs Lots of user support i.e. user guides, online help and forums Operating system Memory management User interface Multitasking Peripherals Security Windows,Android,IOS,Linux Open source software Free to use If you have skilled programmers to hand, the source code can be adapted to suit your particular needs (that is what 'open source' means) May not have as much bugfixing support and security patches as commercial versions Utility programs DO – Disk organisation tools – defragmenter (reorganise hard disk and puts all of the free space together) SM – System maintenance tools, system cleanup,auto updates,anti spyware S – Security – Firewall, antivirus Proprietary software Proprietary software legally remains the property of the organisation, group, or individual Stable product – reliable, lots of bug fixes Support in a timely manner – updates, help Usability – standard interfaces, features Custom written software Software written specifically for you The company will get the exact software/system that they need The software will work exactly how they want it to work Only has features that they specifically need in their business. Open source – things to discuss QLEF Database DBMS Entities and tables Database – Key files POSD Separation from apps and benefits Entity - An object or thing of importance about which data is captured Foreign key - A field used in one table to represent the value of a primary key in a related table Primary key - A field in a table which uniquely identifies each record in that table persistent, organised store of data in electronic form Custom data handling Table - A set of data elements organised in fields and records Database – Forms Database – Queries Database – Reports Database – Modules User interface tool which allows a user to enter or change data in a table Database management tool used to retrieve information based on specified criteria Database management tool used to present information to the user in a professional way Database software and languages contain modules pre-written programs. SELECT * FROM PUPILS grade > C [Make] = "Ferrari" AND [Price] < 8000 " Networks Hubs/Switches Wireless access points Client server More than one computer connected together Hub - broadcasts data to all devices on a network. This can use a lot of bandwidth as it results in unnecessary data being sent - not all computers might need to receive the data. Switch - stores the MAC addresses of devices on a network and filters data packets to see which devices have asked for them A networking hardware device that allows a Wi-Fi compliant device to connect to a wired network (part of your Wi-Fi router) Network type where a computer is a server and others are peers. Peer to peer WAN LAN vs WAN IP address Network type in which every computer can act as a client or server, with no central servers A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs) A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, or office building Unique number assigned to every computer or device connected to the Internet Share files and devices (e.g. printers) Site (software)licences are likely to be cheaper than buying several standalone licences Users can collaborate (work together) Server - Software that provides services to a client, or the hardware that is running it, Client - Software or hardware that requests services from a server Network topology Network topology Network topology Standalone Bus – label the terminators, server, workstation Ring – label the server, cable, workstation Star – label the server, hub, cable, workstation A computer that is not connected to a network All software is installed on the standalone computer. It doesn’t share peripherals with any other computer Network topology Network topology Network topology TCP/IP Bus Ring Star – TCP/IP (also known as the internet protocol suite) is the set of protocols used over the internet. It organises how data packets are communicated and makes sure packets have the correct data (so they can get to their destination without a problem) easy to install cheap to install, as it doesn’t require much cable if the main cable fails/damaged whole network will fail more workstations are connected the performance of the network will become slower because of data collisions can transfer data quickly, even if there are a large number of devices connected because the data only flows in one direction, so there won’t be any data collisions. If the main cable fails or any device is faulty then the whole network will fail. very reliable – if one cable or device fails then all the others will continue to work high performing as no data collisions can occur very reliable – if one cable or device fails then all the others will continue to work expense to install MAC address DNS server A unique number permanently assigned to every physical interface on a computer network (the serial number of the network hardware) Computer within an ISP network responsible for matching up host names to IP addresses HTML Compression The computer programming language hypertext markup language used for displaying web pages in a browser The process of reducing the physical size of files Lossy – some of the quality of the original file is lost Lossless – none of the original file quality is lost Internet Router A worldwide collection of computer networks Device that forwards data packets to the appropriate parts of a computer network WWW - The world wide web is a collection of webpages found on a network of computers (internet). Your web browser uses the internet to access the web Algorithms Test data A series of steps designed to solve a problem The data you use to test part of your program e.g To test a maths quiz you might enter “24” or “4.2” normal data or “Bob” – erroneous data Flow charts High level language Machine language Translator Diamond – Decision Parallelogram – Input/Output Rectangle - Process Programming languages which are similar to natural languages Binary instructions used by the CPU Converts high level languages to machine code Assembler Compiler Interpreter IDE Utility which converts low level code into machine code Utility which coverts high level code into low level code, whole blocks of code at a time Utility which coverts high level code into low level code, one line at a time Software which provides a number of dedicated tools for software developers (IDLE in python) Error diagnostics Run time environment Translator Auto documentation Converts assembly language into machine code ADD 02EA Compiled program runs very quickly. Difficult to find errors Syntax and execution errors can be quickly identified Variables and constants Variables A value stored in memory that can change while a program runs Constants A value stored in memory that cannot change while a program runs Pseudocode Data types Real(float) eg 10.3, 12.5 Integer eg 10,12 Boolean eg True/False Character eg A, space,! String “Hello world” Pseudocode For everything within the “grade” If 4 is less than 5 Add 5 to 4 Print the result Otherwise Print "no" Case based on Grade Case >=100 Report “Perfect Score” Case > 89 Report “Grade = A” Lists and Arrays Errors Array - (like a list) is a series of memory locations – or ‘boxes’ – each of which holds a single item of data. All data in an array must be of the same data type List - data structures similar to arrays that allow data of more than one data type Syntax - A type of error that occurs due to incorrect spelling or grammar in a program Pseudocode Pseudocode Logic - A type of error that occurs due to incorrect algorithm design Ethical right and wrong as far as programmers are concerned: Don’t take bribes Don’t do tasks you cant do a good job of Avoid injuring others Don’t hard the profession Environment Energy – energy used by computers, air conditioning, thinking about sustainable resource/environment friendly, reuse equipment, make things reliable Disposal of equipment – recycle at the environmental centres as they can be hazardous Legal Legal Computer misuse act (hacking/theft) Data protection act Unauthorised access to computer material Unauthorised access with intent to commit Unauthorised modification of computer material. Making, supplying or obtaining anything which can be used in computer misuse offences. The Data Protection Act (DPA) is a law designed to protect personal data stored on computers or in an organised paper filing system Find out the 8 principles