They flollow introductions from the user and from the computer progammer.

The hardware is the components that are interconnected. The computer needs all those components, buy they are independent and we can change any of them.

The basic componets are the CPU, the memory, the graphics card and the peripherals.

The central processing unit is also called "the processor". It is the "brain" of the computer; it looks at the information and takes decisions based on logic.

1. Hard disc: Also called "hard drive", it is a set of rigid discs with a magnetic surface. It stores all your programs and files.

   • Advantages: It can store a large amount of data (today around 1 TB). We can save and erase the information when we want.

   • Disadvantages: It is relatively slow: compared to other types of memory, it takes longer to read and write information.

     
     

2. RAM (Random Access Memory): This is a green plastic card with chips. The RAM is installed in a slot on the mother board. Mother boards have empty slots so that we can add more RAM if we want. The RAM stores the applications and files that we are using.

   • Advantages: It stores (writes) and retrieves (reads) quickly.

   • Disadvantages: We lose the work if there is an electrical power cut. Small memory capacity (around 6GB) compared to the hard disk.

• CDs, DVDs: We call them "optical memories" because they use light to work.

  • Advantages: Cheap.

  • Disadvantages: Not good to rewrite.

    
    

• Pen drives, memory cards: They store the information in chips.

  • Advantages: Rewritable. Quick.

  • Disadvantage: More expensive than a CD or a DVD.

It defines the format of the graphics and helps the processor to process the graphics faster.

We need a powerful graphics cards to play video games, to watch movies and for graphic design.

It is the logic that the computer follows.

The programmer writes instructions. A set of instructions is a "program". When we use a program, the computer follows the instructions in the program.

The OS defines the internal logic for the functioning of the computer.

To program the OS, we must know which are the components of the hardware and how they are connected.

For example, when we tell the computer to switch off, the OS decides to first close the applications, then to transfer all data from the RAM to the HD, and finally to switch itself off

Operating systems evolve along with computers. In the 1980s only one user could interact with a computer and computers only had text, not images.

Computers had one processor, one application, one floppy disc, one keyboard and one screen.

The OS was programmed only to manage those hardware components.

In those days, the OS was stored on a floppy disk, which was loaded after switching on the computer.

The user first loaded the OS, (stored on an external disk) and then the application (stored on another external disk). The user could then start to use the application

It can manage multiple applications at the same time.

It has a graphic display, so we can interact with the computer using a mouse.

It can connect to the internet

Today, the most common operating systems are those sold by Microsoft: Windows Vista, Windows 7...

Microsoft's Windows has a long history which started with the OS called "DOS" (Disc Operating System).

Apple Macintosh is another company which offers an OS for computers. The "Mac" is preferred by graphic designers and artists.

LINUX is a free OS. "Free" means that users don't have to pay to use it, and that programmers can modify the OS as they like.

There are also various OS for mobile telephones.

• Entry peripherals. Entry peripherals give information to the computer: keyborard, mouse, microphone, thermostat...

• Exit peripherals. The computers uses the exit peripherals to give information to us or to an actuator: screen, speakers, printer, light bulb, motor...

A peripheral can be both entry and exit; an example is the router to connect to the internet.

The router receives information from the internet and sends information to the internet.