Many people assume that tablature ("tab" for short) is a modern invention, used only by guitarists who haven't learn to read music. In fact, tab has a long history, stretching all the way back to the 15th century. Pieces written for the lute and Baroque guitar were all written in tab only.
This beautiful manuscript is for a piece of music written for voice accompanied an instrument called the vihuela. Notes to be sung are in indicated in red and the lyrics are printed below. The rhythms are shown above the staff. If a note doesn't have a rhythmic value above it, then you just keep using the previous note value.
Before tab became standardized, German, French and Italian ways of writing tab were all very different. Sometimes, the lowest line would represent the highest sounding string (as some beginners often assume today), and sometimes letters were used instead of numbers.
Take a look at this extract from a piece by Adrian le Roy (c.1520-1598):
In this tab "a" means an open string, "b" means fret 1, and "c" means fret 2. The letters are written in the spaces rather than on the lines and the highest space refers to string 1. The "3" at the beginning simply means that there are three beats in the bar. The dots indicate right-hand fingering (a single dot means index finger).
Here’s the exact same extract in standard notation and modern tab:
Standard notation and tab both have their advantages. It's a good idea to be able to read at least a little standard notation because this will give you a deeper understanding of music than if you just rely on tab alone. It will also let you read music written for other instruments more easily.
However, as a quick, convenient way of writing guitar music, tab has a long history and is clearly set to be around for a long time to come.