Computer Systems

Computer Systems

1. A computer system consists of hardware and software that work together to process data and complete tasks

   • Hardware is the the physical components of the computer like the CPU and motherboard as well as peripherals.
   • Software is the programs that a computer system runs. The two types are application which do tasks for the user and system which are required to allow the computer to function.
   • Embedded systems are built into other devices. Often used as a control system, they are dedicated to one task and are easier to design and make so they are cheaper to produce

2. CPU

   • The central processing unit is the brain of the computer. It processes all data and instructions.
   • The control unit is in overall control and executres program instructions. Controls flow of data inside CPU
   • Arithmetic Logic unit does all calculations which might be arithmetic/relational/logical.
   • Cache which is very fast memory in the CPU. The clock which signals the synchronisation of of instruction carried out. Buses that are collections of wires that transmit data between component and CPU.
   • Von Neumanns Architecture describes a system where the CPU runs the program stored in memory.
   • Fetch-Execute cycle is used to execute instructions. By using the address bus to fetch an instruction from main memory, using the data bus to transfer it to be decoded by the CU, then executed which might be by the ALU or CU.

3. Memory

   • Memory is where data is stored permenantely or temporarily and is a fundamental part of computer systems.
   • RAM is high speed volatile memory that stores data, files and programs whilst they are being used by the computer. It acts as the main memory. It can be read and written to but loses its data without power.
     • ROM is read only memory that is nonvolatile and stored the operating system as well as the instructions the computer needs to power up (BIOS). The data on this is permenant with or without power.

4. System Performance

   • Clock Speed is the number of instructions a single processor core can carry out per second. Higher clock speeds mean more instructions can be done in shorter speeds of time. However increasing the clock speed may make the CPU overheat so extra fans are needed.
   • The number fo CPU Cores can affect the speed as each core individually processes data. More cores means more instructions can be executed at once.
   • Cache is small storage on the CPU which is faster than RAM. There are 3 levels. The higher the level the more it can store but the slower it is. Cache speed is dependant on how far it is from the CPU. L1 is the closest and L3 is the furthest.

5. Secondary Storage

   • Secondary storage is storage that is nonvolatile storage that isn't directly accesible by the CPU
   • Magnetic hard disks are a stack of magnetised metal disks. Data is stored magnetically on small sectors within circular tracks. There is a read/write head on a moving arm used to access the sectors. They are cheaper per GB but less durable due to moving parts
     • Solid state drives have no moving parts and use flash memory which works by trapping electorns. It is faster and more portable but more expensive.
   • Optical discs are things lide CD's which use microscopic indentations to store data. They are cheap and portable and won't be damaged by water but are slow and can be scratched.
     • Cloud storage uses the internet to store files and data in a server in a remote location. Users can access data from anywhere and have a lot of storage but it can only be accessed by internet which makes it vunerable to hackers

6. OS

   • Complex system that runs and maintains a computer system found on most computer system and has many roles.
   • Communicates with peripherals using drivers allowing computer to take in inputs and give outputs
   • Manages applications by giving access to hardware and provides interface (GUI)
   • Manages memory by removing and inputting data inro RAM and controls how much access each program has.
   • Gives processes time slices with CPU to help get an efficient order of executing instructions.
   • Deals with management of file and disk management using defragmentation and organisation of files.
   • Manages system security through user account control to allow each user specific access to particular data.

7. Utilities

   • Any software used to maintain or configure a computer.
   • Encryption software scrambles data to prevent third-party access. Can only be decrypted with a key.
   • Files stored on hard disks are stored in any available space. From moving and deleting files there becomes gaps on the the disk and so the OS has to split files to fill those gaps. Defragmentaion reorganises the files to become one block.
   • Compression reduces file size to take up less disk space.
   • A backup is a copy of the computer systems files and settings stored externally to be restored in case of data loss.
   • Virus scanners inspect each file on your computer looking for viruses.