varchar - storage and performance

[Anon]

I have two questions concerning a varchar field.
Firstly, does the varchar use up much more storage space than a normal char field. For example would a 75 charactor varchar be more efficient than storing this in a char(100)? Or is there an overhead in creating the varchar.

Secondly, does the performance of queries suffer as a result of using the varchar?

thanks

[Anon]

Varchar takes up as much space as the characters you put in, plus 2 or 3 bytes overhead.

char fields allways take up as much space as you reserved for them, plus 2 or 3 bytes overhead.

So, a varchar usually takes up less space than a char field.

Reading varchar is just as fast as char,
but updating varchar could be slower becaus of the change in required space in the database file.

But I don't think you'll notice unless you do 100k queries at a time