Questions

‘Sitting on the fence’ is the correct idiom used. It is used to describe a person’s lack of decisiveness, neutrality or hesitance to choose between two sides in an argument or a competition, or inability to decide due to lack of courage. Thus, the sentence is grammatically and contextually correct. Thus, the correct formation would be, ‘Decide one way or the other; you can’t be sitting on the fence forever’.

The First Generation Computers size was very large. 

Since the First generation computers used 1000s of vacuum tubes that required lot of space made them gigantic in size. Single transistor could replace 1000 vacuum tubes and a single IC chip replaced 1000s of transistors made computers smaller and more speedy.

It is obvious that computers developed with more power, reliability, speed and smaller sizes due to the enhancement of technology.