How many computers did IBM believe that could be sold worldwide when they invented the term 'personal computer' (PC)?

Explanation

A personal computer (PC) is a multi-purpose computer whose size, capabilities, and price make it feasible for individual use. PCs are intended to be operated directly by an end user, rather than by a computer expert or technician. Early computer owners in the 1960s, invariably institutional or corporate, had to write their own programs to do any useful work with the machines. In the 2010s, personal computer users have access to a wide range of software.