The PAD is short for "scratch-pad". It is a temporary storage area for strings. It is heavily used by 4tH itself, e.g. when you print a number the string is formed in the PAD. Yes, that's right: when you print a number it is first converted to a string. Then that string is 'COUNT'ed and 'TYPE'd. You can even program that subsystem yourself as we will see when we encounter formatted numbers.