Computer Science.Paper 1

Computer systems
1. It is able to take a set of inputs(Provides data to the computer) ,process them and create a set of outputs (Provides the processed data in a format that the user can understand and use.)
2. Processing involves manipulating the input data
3. A bus is a set of wires which provide the system with instructions are called software.
4. An ebbedded computer system is one that is part of a larger piece of equiptment such as a television and has a specific task to carry out.
CPU
1. The purpose of the CPU Is to process data.(It is where all the searching ,sorting ,calculating and decision making takes place) It fetches instructions from the memory (RAM) and decodes them and the exicutes them.
2. is an electric chip called a microprocessor (Also known as the brain of the computer).
3. It also controls all the other componenets of the computer for example: Hard disk and sound system
4. Located on the motherboard
  1. The CPU runs at the speed of its clock
5. 1. It consists of billions of transistors which are tiny electronic switches which are either on or off
  2. There are three sections inside: Control Unit , Arithmatic Unit(ALU) and registers.
    1. These are the Data Bus, which carries the data, the Address Bus which carries information on the location of the data and the Control Bus, which handles commands to control devices such as the hard disk, the monitor and the graphics card.
6. Control Unit
  1. It Has 3 main Jobs
    1. 1) It controls the way data moves around the CPU (Timing signals)
    2. 2)It executes the instructions provided by the program (Control signals)
    3. 3) it controls and monitors the flow of data between the CPU and the other components such as input devices ,memory ,graphics card ect (signals to memory /devices)
7. The cache is a very fast but small type of RAM
8. CPU Performance factors.
  1. Things that determine the performance are: Clock , Cores , Cache ,size of RAM and the Graphics Card.
  2. With each tick of the clock, the CPU can process one instruction. in aCPU with a typical clock speed of 3.5 GHz, this means that 3.5 billion instructions can be processed every second
    1. So the higher the clock frequency, the faster the CPU can run and the more instructions that can be processed every second.
    2. Every time the clock ticks, a bit of power is used and that power causes heat to be generated. If you go higher than a clock frequency of around 3.5-4GHz, the heat will damage the chip itself.
  3. Cores
    1. Every time the clock ticks, a bit of power is used and that power causes heat to be generated. If you go higher than a clock frequency of around 3.5-4GHz, the heat will damage the chip itself.
      1. Multi-tasking is the ability to carry out more than one task at the same time. Clearly, with two cores, a CPU can run two tasks simultaneously. A quad core can handle four simulateous tasks. So for example, one core could be running a photo editing application whilst another is handling a word processing application.
      2. Parallel processing is when a single task (program) is split into two or more parts and each part is processed at the same time. In theory this would double performance on a dual core cpu as each part is processed independently. However, you do not always get twice the performance because many programs cannot be split neatly into two independent parts. This is because they are mostly sequential i.e. each task depends on the outcome of a previous task and so it has to wait for the first task to be completed. An example where parallel processing is possible is a task to update all the pixels on the screen. The colour of one pixel does not tend to depend on another pixel
  4. Cache performance
    1. Having a larger cache will speed up processing because the CPU can access data and instructions faster than they can from RAM.
    2. However, cache memory is more expensive than standard RAM
  5. RAM capacity
    1. A computer always comes with a certain amount of RAM and this will most likely be enough for light use. But if you want to have a larger number of applications open all at the same time there may not be enough RAM available for your computer to operate smoothly
    2. In this case some applications are either not loaded at all, or they get swapped out to 'virtual memory'.
      1. Virtual memory is an area set aside on the hard disk to act as a very slow form of RAM. The operating system creates a 'swap file' in virtual memory. Virtual memory will be used to store some of the currently running programs and data if RAM is full.
  6. Graphics card
    1. The graphics card contains a 'Graphics Processing Unit' or GPU which is designed to handle graphics and images much faster than the CPU itself. If an application is making intense use of graphics or video then installing a GPU will improve performance considerably. The CPU will send any graphics related tasks directly to the GPU while it continues to process other tasks.
    2. Although installing a graphics card will lead to improvements in computer performance there are some issues that need to be considered:
      1. Graphics cards can be expensive.
      2. Graphics cards do not improve CPU performance on all tasks, only ones related to graphics and other large files.
      3. Graphics cards use a lot of power and this might mean that the computer also needs to be fitted with a more powerful power supply. The larger power supply will add further cost.
      4. Because graphics cards use a lot of power they need a cooling fan. The cooling fans are noisy so they make the computer sound louder than they were before the graphics card was installed.
Von Neumann Architecture
1. Another name for it is the stored program computer
2. Is not an actual computer but the idea of how a computer could be built.
3. Includes program and data loaded into the memory
4. Registers in a CPU includes the Memory Data Register (MDR) and the Memory Address Register (MAR)
5. The Program Counter contains the the address of the next instruction
6. The Accumulator holds temporary data whilst processing is underway.
7. Modern CPUs include a number of extra general purpose registers to make programs more efficient than having a single register needing to contain every temporary data item.
Fetch -Decode - Execute
1. Software or program is initially loaded into main memory (RAM)
2. A process called the Fetch-Decode-Execute cycle handles each instruction one at a time.
3. The cycle also handles the loading of data from memory
4. The first stage is 'Fetch' which loads an instruction or data from memory into the CPU
5. The second stage is 'Decode'. The instruction is decoded by the Control Unit so the CPU can handle the last stage
6. The third stage is 'Execute' which means carry out the instruction
Main memory
1. Main memory is any memory that is directly accessed by the CPU. Examples of main memory include Random Access Memory (RAM) ROM chips
2. Memory can be divided into two types: main memory and secondary storage.
3. Registers and internal cache are not considered main memory as they reside within the CPU. Hard disks and flash memory are examples of secondary storage. When the CPU needs to use programs or data from the hard disk, they are first loaded into main memory, and are accessed from there.
4. Main memory can hold more than one program at a time, which makes it quicker for the CPU to swap between tasks. Secondary storage is used for holding large amounts of data and programs long-term, but can only be accessed relatively slowly.
5. Volatile Memory
  1. Volatile memory is cleared whenever the supply of power is lost. In contrast, non-volatile memory will continue to hold anything it was storing even if it is not receiving any power.
    1. Volatile memory includes RAM, CPU registers and the cache.
6. RAM
  1. RAM is used as main memory. It is accessed directly by the CPU
  2. RAM is volatile memory. If it loses power, the data it holds is lost
  3. RAM holds billions of storage locations, each with its own memory address
  4. There are two type or RAM, namely DRAM and SRAM.
    1. Dynamic Random Access Memory (DRAM) is what you will find in a RAM module DRAM is commonly used for main memory because it is relatively inexpensive. However, it needs to constantly receive a "refresh signal" to keep its capacitors charged, otherwise it will lose the data it is holding.
    2. Static Random Access Memory (SRAM) is commonly used for the cache. This is because it is much faster to access than DRAM. Also, SRAM does not require a refresh signal.
secondary storage
1. Because main memory (RAM) is volatile, any data or programs currently being stored there will disappear once the power is lost i.e. the computer is switched off. And so secondary storage is used to retain a copy of programs and data that need to be kept long term.
2. Storage devices and media
  1. A secondary storage device is the physical hardware that carries out the storage action
  2. Some storage devices come with removable media. For example a DVD writer burns a blank DVD. The DVD itself is an example of storage media. Storage media is the physical object used to actually store the data.
3. Magnetic storage
  1. This uses minute magnetic particles or 'domains' to store data. A hard disk is an example of a magnetic storage device. It contains several platters on a spindle, spinning at high speed, with read/write heads floating just above the surface. Another example of magnetic storage is a magnetic tape cartridge.
4. Optical Storage
  1. Optical storage includes CD, DVD and Blu-ray disks.
  2. A laser beam burns tiny dark pits on to the surface of the optical disk. If a pit is present, this can represent a data bit being '1' and if no pit is present, this can represent a data bit being '0'.
5. Solid state media (Flash)
  1. Solid state media includes USB memory sticks, Solid State Drives and SDHC memory cards (as found in digital cameras)
  2. Solid state media hold data using electronic switches. If the switch is open, it represents a '1', since it retains an electric charge. If it is closed, it represents a '0'. It is an electrical form of storage, unlike magnetic or optical media. The technology is called 'Flash memory'.
6. Data Capacity

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