There are three basic font types:
All three have a place in the world of fonts and all are better than the others in certain circumstances. Each type will be taken in turn.
Bitmap fonts
Bitmap fonts are, as the name implies, bits or dots that make up the characters just like marking the dots on a piece of graph paper. These dots are sometimes referred to as PIXELS standing for PICture CELLS.
They may seem to be crude and old fashioned, especially when compared with the modern TrueType or Adobe fonts that are used today. However, they are the basis for all fonts. The VDU screen consists of dots/pixels and all fonts displayed as Bitmaps on screen. Similarly, a laser printer prints in dots, small ones, but dots.
In the end screen and printer fonts have to end up as Bitmaps. The major exception to this is the case of plotters, more of this under Vector fonts below.
The big drawback of Bitmaps is that each size (point size), italic, bold version requires a separate font. Scaling Bitmaps is full of hazards. Increasing scale can cause big square steps that look ugly. In fact all lines that are not exactly vertical or horizontal are made of dots that are in steps, enlarging simply makes the steps larger.
Decreasing scale is usually alright for small changes, but for larger changes the arithmetic errors, rounding errors start to appear. Two lines that started the same width can end up different widths, two dots instead of three. Again the result is ugly. Scaling Bitmap fonts requires that a suitable Bitmap font Editor be available to sort out the resultant uglies.
So why does Windows arrive with eight Bitmap fonts as standard, several of them containing about six point sizes? The reason is simple, for the smaller fonts that are used regularly on screen the best results are ready made, hand crafted Bitmap fonts, each made specially for the job they are designed to do. Some of the smaller fonts in the SMALLF.FON font are barely readable, but they can convey a meaning.
More importantly to some, there are printers that can print at 200 pages per minute and more. These demand printer fonts that can keep pace, Bitmaps again. Also there are a number of special applications that use Bitmaps.
Vector fonts
Vector, or Stroke, fonts make up their characters by drawing straight lines. A curve is drawn with several short straight lines. A character consists of a series of points that are joined up to make the character.
Because of this these fonts can be scaleable. By adjusting the scale on which the points are drawn then the size of the character can be changed easily. If the size becomes too large then the straight lines start to be obvious and that represents the largest useful size of the font.
Vector fonts are used extensively in plotters, rather than printers and are well known in the fields of draftsmen and architects. They also were the first scaleable fonts used in Windows 2.0 and 3.0 under the names of Modern, Roman and Script.
Since the introduction of Truetype fonts the Vector font is little used in the Windows environment.
TrueType fonts
TrueType, or outline, fonts have now taken over much of the computer Typographical work. They, together with Adobe Type 1 fonts, are constructed with outlines. A letter 'O' has two outlines, one outside and the other inside and the TrueType engine fills the gaps between the two.
The outlines are drawn with straight lines and curves. Most computer users have come across Bezier curves used to created curves in drawing packages. Adobe uses Bezier and TrueType uses B-Splines, which are similar. A dot is placed 'off-curve' and acts like a magnet bending the line into a curve.
Because the construction is mathematical, then the size can be changed easily, similar to Vectored above. When these size changes are made the smooth curves are preserved entirely because of the curve handling.
Other things are possible, like italic and bold. Complex routines are available to control the character's appearance under many situations. These routines are usually referred to as Hinting. Pleasant characters may be made without any hinting but the best fonts carry large numbers of hinting instructions the ensure that characters are rendered in the best possible way. There is an article on Hinting in this library.
The TrueType format includes many tables of data to assist in providing the best possible perfomance.