The term file refers to the space on either a hard disk or floppy disk for storing information.

Try to imagine a file as a parcel. The parcel is stored in a certain place, while its size and appearance usually provide you with no clues as to its actual contents. This is just the same with a file. A file is moved from one folder to another, just like a parcel is taken from one department to the next.

Opening a file poses no problem in itself. But as with a parcel, it is a question of whether a program can make any sense of the contents once a file has been opened.

In general terms, it is the contents of a file that are usually being referred to when you talk about opening or importing a file.

Let us assume, for example, that the parcel contains a letter which has characters you cannot read. This means that the contents of this letter are not directly accessible to you. If you know that the letter is written in Chinese, however, you can call upon a translator, who can then translate the letter into your own language.

The same applies when you open a file, i.e. you also have to know which "language" it is written in. The term "language" is what is known as the format of a file. The format defines the way information is written into a file. This is helpful in allowing the information to be read again afterwards without any of it being lost.

Similarly, if a program is to read a file containing "Chinese" characters, a translator also has to be brought onto the scene. This translator is known as a filter in computer terminology. The filter refers to the part of the program responsible for translating information from one format to another. It does not matter whether we are talking about translating from an external to an internal format or vice versa. Since the translation process to a large extent takes place independently from the main program itself, filters are often programs in their own right. In IsoDraw, the filters for all the formats come ready installed in the main program.