GCSE Computing

GCSE Computing

1. Computer Systems

   • What is a computer system
     • A computer system is a set of parts, including the computer itself, that work together to perform tasks. It is based on processing data and producing information
   • Importance of Computer Systems in the modern world
     • Computer systems are involved in most human activities. A few examples are for Safety (controlling trains and guiding aircraft) and for Travel and entertainment
   • Need of Reliability in computer systems
     • As we become more dependent on Computer Systems, we need to be able to trust their reliability. The computer systems the we interact with are usually so reliable that we don't give them much thought. However computer systems can sometimes let u down. Unreliable computer systems can cause serious problems e.g. aircraft accidents

2. Computing Hardware

   • What is a Computer hardware
     • Hardware is the term that describes the physical components of a computer system, anything that can be seen or touched.It includes input, output, storage and processing devices.

3. The Central Processing Unit (CPU)

   • What is the purpose of the CPU
     • The purpose of a CPU is processing data
   • The Fetch, execute cycle
     • When the computer is switched on it starts to run an endless fetch–execute cycle The programs the CPU needs to process are stored in the main memory. The CPU fetches the next instruction, decodes it and executes it before repeating the process.
   • How common characteristics of the CPU effect it's perfomance
     • The number of cores – how many instructions it can process at a time. A multiple core processor has more than one CPU In a dual core CPU, two CPUs work together. Since these can fetch, decode and execute instructions at the same time, the computer is able to process more instructions.
     • Cache memory is very fast memory that can work at speed similar to the CPU, but it is very expensive and only used to store data waiting to be processed by the CPU. Cache memory is usually provided in much smaller sizes than the main memory, megabytes, MB as opposed to gigabytes, GB (1GB = 1024 MB). Cache memory is located very close to the CPU to minimise access times.

4. Binary Logic

   • Why data is represented in Computer Systems in Binary form
     • Computers use binary because 1 and 0 can be represented very easily using simple electronic components set into the ON or OFF state (a switch).
   • Logic Gates
     • In the NOT gate, if 0 is input then it outputs 1; If 1 is input then it outputs 0. The AND gate outputs 1 only if both inputs are 1. The OR gate outputs 1 if either of the inputs is 1.

5. Memory

   • The difference between RAM and ROM
     • RAM is volatile and ROM isn't. RAM is also much larger than ROM, however the contents can't be changed in ROM but can in RAM
   • The need for ROM in a Computer System
     • ROM is often used to store the boot program, a sequence of instructions to start the computer and load the operating system.
   • The purpose of RAM in a Computer System
     • RAM stores the programs and data that the computer is currently working on. The operating system will also be loaded into RAM in order to run.
   • Cache Memory
     • Cache memory is used next to the CPU to provide very fast access to data. Cache is used between the main RAM and the CPU to improve performance by holding the data that has just been, or is just about to be, processed. Cache memory is a much more complex design than standard RAM, is more expensive and only available in much smaller sizes, so is not suitable for main memory