Topic 2

Topic 2

1. input and output

   • An input device is a piece of hardware that is used to enter data into a computer.
     • eg. mouse keyboard and mic
   • something that outputs the data from the computer
     • screen, speakers, printers

2. ram and rom

   • ROM is a special kind of memory which stores the instructions which the computer uses when it ‘boots up’- the BIOS (Basic input output system). It allows it to check the type of hard disk installed, the amount of RAM installed and the type of CPU being used. The information on a ROM chip is often programmed at manufacture
     • • PROM (programmable read-only memory) - manufactured as blank ROM. PROM chips can be bought cheaply and programmed directly by a programmer. They are not rewritable so they can only be programmed once. • EEPROM (electrically erasable programmable read-only memory) - popular in PCs and smartphones as the firmware can be easily updated by the manufacturer. Th
   • This is because your work was stored in Ram. Anything stored in it will be lost as soon as the power disappears. This is known as volatile memory. When the computer is first switched on RAM will be empty because it is volatile and needs power to maintain the contents. RAM is also referred to as Main Memory.
     • • Dynamic RAM, which can only hold a charge for a few milliseconds and must be constantly refreshed. DRAM is usually used for the main memory. • Static RAM, which does not need to be constantly refreshed, but is a much more complex and expensive design. SRAM is used for cache memory

3. secondary storege

   • Secondary storage is non-volatile disk space, and is sometimes called auxiliary memory, secondary memory or external memory. Storage devices, like an external hard drive are used to store files like photos, program files and any other information that needs to kept long term
   • types
     • Tape storage Big businesses and science projects, which process thousands of bytes of data every second, often use tape storage to back up their data. It is a very cheap and reliable way to store large amounts of data.
     • Optical disks CD, DVD and Blu-ray discs are forms of optical storage. They are a useful lightweight media for transporting data and programs. easliy broken or stracted.
     • The magnetic hard disk is a magnetised rigid plate or stack of plates with heads to read the data as the platters spin around. They spin at around 7200rpm. The data is encoded into bits and written onto the surface as a series of changes in the direction of the magnetisation. The data is read by detecting the changes in direction.

4. virtual

   • A computer will start to slow down if RAM is being fully used. When there is not enough RAM to deal with all the demands on the computer it will use a section of the hard disk as a temporary store for some of the data. This area is known as virtual memory. Put simply it is when a computer uses part of the hard disk to supplement main memory when main memory (RAM) is running low. The operating system makes part of the storage drive available to use as RAM. Virtual memory is much slower than main memory because processing power is being taken up by moving data around, rather than just executing instructions

5. cpu

   • 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.
   • Benchmarking is a test used to assess the performance of a computer. Different types of benchmark software are used for the different kinds of application you might want a computer to do.
   • The CPU processes data and instructions using the fetch-decode-execute cycle. The amount of time that it has to process each piece of data is controlled by a quartz clock inside the CPU.
   • Address bus - this sends information about where data needs to go by sending an address to the memory. The address bus only sends data in one direction - from the CPU to RAM. Data bus - this sends data to the memory or receives data from the memory. Data can flow both ways along the data bus.
   • parts
     • • Arithmetic logic unit (ALU)- This carries out calculations and makes decisions on the data sent to the processor.
     • • Control unit (CU)- This controls the timing of operations and the instructions. It decides where to fetch data from and where to send it to.
     • • Registers- Is a small amount of fast temporary memory within the processor where the ALU or the CU can store and change values needed to execute instructions.
   • purpose
     • Fetch The first step the CPU carries out is to fetch some data and instructions (Program) from the main memory then store them in its own internal temporary memory areas. These memory areas are called ‘registers’ or immediate access memory.
     • Decode The next step is for the CPU to make sense of the instructions it has just fetched. This process is called ‘decode’. The CPU is designed to understand a specific set of commands. These are called the instruction set of the CPU. Each make of CPU has a different instruction set. The CPU decodes the instruction and prepares various areas within the chip in readiness of the next step.
     • Execute This is the part of the cycle when data processing actually takes place. The instruction is carried out upon the data (Executed). The result of this processing is stored in yet another register. Once the execute stage is complete, the CPU sets itself up to begin another cycle once more.

6. binary

   • Binary is a number system using only 0 and 1 to represent all numbers. 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).
     • gates
       • NOT gate The NOT gate is a very simple gate. If 0 is input then the outputs 1 and if 1 is input it outputs 0.
       • AND gate The AND gate tells us if both of the inputs are 1, by outputting 1, otherwise it outputs 0.
       • OR gate The OR gate tells us if one or both of the two inputs are 1 by outputting 1 otherwise it outputs 0.