Why historically do people use 255 not 256 for database field magnitudes?

Question

You often see database fields set to have a magnitude of 255 characters, what is the traditional / historic reason why? I assume it\'s something to do with paging / memory l

Answer 1

A maximum length of 255 allows the database engine to use only 1 byte to store the length of each field. You are correct that 1 byte of space allows you to store 2^8=256 distinct values for the length of the string.

But if you allow the field to store zero-length text strings, you need to be able to store zero in the length. So you can allow 256 distinct length values, starting at zero: 0-255.