GCSE CS Computers

GCSE CS Computers

1. Input - output - process

   • A computer is a machine that takes some kind of input from its surrounding, processes the input according to a give rules, and provides some kind of output.
   • Processing means performing a series of actions on the input according to a given set of rules. So this process is like a sequence of step-by-step instructions, so the process should follow an algorithm to process the full results.

2. CPU

   • Components of a CPU
     • ALU - The Arithmetic Logic Unit (ALU) works everything out. It executes basic arithmetic operations (addition, subtraction etc…) Carries out program instructions.
     • CU - The control unit which performs the tasks of fetching, decoding and managing the execution of instructions and the storing of the results.
     • Decoder - interprets program instructions and tells the ALU what operation to carry out
     • Clock - Controls the rate at which the program instruction are carried out.
     • Buses - Electrical conductors that carry instructions between components in the CPU and between the CPU and other components on the motherboard (e.g. RAM)
     • Registers - memory locations. Some perform special functions in the FDE cycle
       • Program counter - holds the address of the next instruction to be fetched
       • Memory Data register(MDR) - a temporary store (buffer) for anything copied from memory
       • Memory Data register (MAR) - Holds the address of the memory location currently being read (fetched) or written to.
   • Von Neumann Model
     • This is where both the program and data are stored in the memory. Components are: Processing unit/CPU Program counter Memory to store data and instructions Input and output mechanisms
   • Fetch-decode-execute cycle
   • The central processing unit (CPU) carries out(executes) all the stored programs instructions.
   • Clock speed
     • The CPU carries out one program instruction for each clock cycle. Clock speed is usually measured in GHz. 1 GHz is 109 cycles per second. 2.2.GHZ CPU means that its clock ticks 2.2 billion times per second (number of FDE per second)

3. Memeory

   • RAM
     • RAM is the ‘working’ or 'temporary’ memory‘ of the computer. If you switch a computer off whilst working your work usually disappears. This is because it is stored in the RAM. Data does not stay in the RAM permanently, because of this it is known as 'volatile memory'.
     • Works with the CPU to store instructions, Data and programs
   • ROM
     • ROM is a type of memory that retains its data even without power, so even when the computer is switched off, it will not lose the data which is saved onto it Non-Volatile.
     • Data is not erased when the computer is switched off
     • ROM stores the computer’s BIOS
   • Cache Memory
     • Cache memory is very fast memory that is built into the CPU and speeds up a computer by allowing the CPU to access instructions and exchange data with RAM more efficiently by temporarily storing the contents of frequently used memory addresses.
       • Very Fast; Speeds up processing by storing recently or frequently used instructions (so no need to use main memory. Cache is small in Size; It is also expensive in comparison to RAM (Main memory)
   • Secondary storage is any kind of permanent storage to which the contents of RAM/RAM are copied. is non-volatile, meaning it retains its contents without the need for a power supply
     • Solid state
       • Solid state devices are a form of flash memory, it is therefore non-volatile like ROM so the contents are not lost when there is no power supply, but able to be written to as in RAM. This uses electricity to store data as 1 and 0.
         • Solid State Devices offer faster read/write times than either magnetic or optical storage devices. They are also silent and resistant to physical shock which makes them ideal as portable storage devices.
     • Magnetic
       • Magnetic disks are read with a moving head inside the disk drive and magnetic tapes are read by moving the tape past a read-write head. Using 1 and 0’s to represent the north and south within a magnet. Moving parts make these media quite slow to read from or write to and moving parts go wrong
     • Optical
       • They use a surface where a pattern of reflective and non-reflective areas represents the binary data. The reflections from a low-power laser beam read this pattern as the surface moves past it. Typical devices include CD-ROM, CD-RW (Read-Writeable), DVD and Blu-Ray.

4. Cloud storage

   • Users store and backup their data on storage devices, usually hard disks drives on servers, somewhere on the internet on a server. You can only access your data over the internet but you can casses it on multiples devices.

5. Embedded systems

   • An embedded system is one that is designed to do a specific job, usually part of a bigger system, that might have other electrical or mechanical parts, such as a washing machine. Build for a small range of specific task unlike a desktop and laptop computers that are general purpose and are capable of carrying out many different tasks.
   • Embed systems are called real-time systems before they must ensure an immediate response in order for the system to react to different situations. E.g. Digital Camera or Microwave oven

6. Logic

   • The CPU is made up of millions of tiny switches that can only be in one of two states, either 'ON' or 'OFF'. While the processing of data is taking place, the switches will alternate between these two states.
   • Binary logic is applying the binary 1/0 on/off states to true and false statements. (Boolean Statements) 1 = True 0 = False This is representing electronic circuits on the cpu being open or closed.
   • Trust Tables
     • This shows visuals which part of a program runs depending on the certain conditions (this is shown as an if statement). The table will show all possibilities and outputs

7. Operating systems

   • Application software - an end use program e.g. word, photoshop, web browsers or any App
   • System software
     • Runs and maintains the computers system and manages users, this is an OS and utility software
   • Manages users through a user interface
     • GUI - Graphical user interface or a command line
   • Peripheral device management
     • the input and output
       • e.g. Mouse and keyboard
       • e.g. Screen, speakers
   • User management
     • User log in and file permissions
   • Memory management
   • Multitasking - lots of programs running at the same time within the computer system - the OS manages this
   • File management

8. Utility software

   • is a collection of tools which does a specific job to help optimise the system
   • Encryption software
   • Data compression software
   • Backup
   • Defragmentation software
   • Malware and anti-malware software

9. Simulation and modelling software

   • A computer model attempts to abstract the rules and mechanisms that control real-life systems and apply them, n a computer program so that they can be used to simulate the behaviour of those system under different conditions.
   • E.g. Flight simulators Traffic flow Weather forecasting Financial modelling

10. Programming languages

    • Machine code
      • Machine code is the base level of code the computer need to run command. This is written in binary 1’s and 0’s Writing code using binary was very difficult for programmers to read and write programs
    • Assembly Language
      • Due to the difficulties in programming using machine code Assembly language was created. This language used to define the instruction set rather than the binary e.g 1011 and 1001 commands to ADD and SUB. This made it easier to read and write code Assembly still translated the command/words back to machine code.
    • High level languages
      • High level languages do not have a one to one correspondence between the command and machine code One command in high level could represent lots of machine codes e.g. INPUT a or OUTPUT a+b All High level code need to be translated to machine code before it runs

11. Translators

    • Is a program that is able to convert high-level language command into a set of machine code commands.
    • Compilers
      • The compiler converts all the high level source code to machine level object code before attempting to run the code it produces. The object code can be save and run independently from the source code e.g. creates a separate executable file
    • Interpreter
      • Converts the source code one instruction at a time into machine code then runs it before translating the next instruction It does not create an addition object It must be translated from the source code every time

Imagens e arquivos do mapa

• What Is an Embedded System? (Incorporar)
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• The Central Processing Unit (CPU): Crash Course Computer Science #7 (Incorporar)
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• Boolean Logic & Logic Gates: Crash Course Computer Science #3 (Incorporar)
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