Computers

Computers

1. Hardware

   • CPU
     • Uses the Fetch-execute cycle
     • Uses Von Neumann architecture
       • Registers are small storage areas for use during execution of an instruction
       • Program Counter (PC) - stores the address of the next instruction to be fetched
       • Current Instruction Register (CIR) stores the instruction currently being executed
       • Accumulator (ACC) stores values currently being processed
       • Memory Address Register (MAR) stores the address to be read/written in main memory
       • Memory Data Register (MDR) stores the data to be read/written to main memory
       • The Arithmetic Logic Unit (ALU) performs mathematical and logical operations.
       • The Control Unit (CU) / Clock decodes the program instruction in the CIR, selects machine resources and operations, and coordinates activation of those operations.
     • The steps of the fetch-execute cycle are:
       • 1. The memory address in the PC is copied to the MAR
       • 2. The instruction stored in the memory location contained in the MAR is transferred to the MDR
       • 4. The PC is incremented, ready for the next instruction
       • 5. The instruction in the CIR is decoded and executed by the CU, potentially making use of the ALU
       • 3. The instruction now in the MDR is copied to the CIR
     • Speed pf the CPU is dictated by these variables:
       • Clock Speed - The faster the clock speed, the more instructions can be fetched and executed in a second, this is measured in Gigahertz
       • Number of Cores - having multiple cores allows several instructions to be fetched and executed at the same time
       • Cache Size - cache memory is extremely fast memory, used to store frequently used instructions and data, more cache memory improves performance as more instructions can be stored, meaning fewer are needed to be fetched from RAM
         • L! Cache - smallest and fastest
         • L3 Cache- Biggest and slowest - still faster than RAM
   • Secondary storage types
   • Additional Components
     • GPU - has 100s or 1000s of specialised cores, designed to rapidly manipulate memory and perform specific mathematical operations, does vector calculations
     • Sound Card - manipulates audio - plays audio through speakers
     • Motherboard - connects all the components together
   • Embedded Systems
     • A small computer that forms part of a larger system, device or machine e.g GPS systems, engine management systems and electronic calculators
     • Advantages
       • Limited number of functions
       • Tend to require less power
       • Less processing power

2. Software

   • Operating Systems
     • Collection of programs that manages and controls the computer ( file management, process management, hardware management and user interface management
     • Examples: Windows, macOS, Linux, Android, IOS
     • File Management
       • creates a virtual file structure of the physical components. It is a hierchal structure starting with the root directory, like a tree
       • Includes meta data for date created, modified and last time it was accessed. The last backup, file creator, access permissions and file size
       • Users can perform functions on files like creating, naming, saving, copying, moving and deleting
     • Process Management
       • Each program is made up of program instructions. When some of these instructions are runing, this is a process. The operating system uses multiprocessing to allocate use of the main memory and the CPU
       • Multiprocessing can be used only when there is more than one processor in the system. This is common in most computer systems nowadays. This means that several processes can execute at the same time. A scheduler is used to time the different processes, task manager shows this
       • There are several different scheduling algorithms, which all have certain similarities: - they all use a queue to hold waiting processes -they all use the clock cycle to time the execution and they all switch between processes
         • FCFS - first in, first out queue, processes arrive, are executed then leave the queue in order, a slow algorithm because all the processes have to wait for the previous one to finish
         • Round Robin - Much more efficient, each process is given a fixed amount of time, then it is switched out and sent to the back of the queue
         • Priority Based - each process is given a priority based on several things, including how much time it needs and the memory it will use. A process with a higher priority will be executed before a process with a lower priority
     • Hardware management
       • Device drivers are needed to be installed for each new input or output device, device drivers allow devices created by different manufacturers to communicate
       • Resource management - when a process is running it may need to use resources such as printers, hard disk drives, memory and the processpr. The operating system allocates the required resource to the processes that are currently running, ensures that any data or instructions do not conflict with each other
     • User interface management
       • The user doesn't need to know about the hardware, so the operating system uses virtualisation to give the user the impression that they are interacting directly with the hardware, the user sees a virtual machine giving access to logical devices. The operating system translates the user's actios to match to the physical devices
       • Users are granted different access permissions to perform tasks. A networked system would allow acces to data they need, security features such as usernames and passwrods, are included to protect the systems, the operating system can keep track of different users and what they are doing/.
       • System administrators have special privileges to maintain the computer system. This may include being able to add users and give them access
       • A GUI is used in most PCs and laptops, uses WIMP (windows, icons, menus and pointer) to describe the features of this interface. Applications are represented by icons, and can be accessed through menus, users interact with a mouse. - require more processing power
       • CLIs are text-based. Users control the computer by typing commands, uses little processing power and are extemely powerful, but takes longer to learn how to use them
       • Mobile interfaces are similar to GUIS except they respond to touch, and are single-user operating systems

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