The first "Windows" concept was the Xerox Alto, which was designed in 1973 at Xerox's Research Center in Palo Alto, California (They also designed the first laser printer in '69 which was available commercially in '78, not the sort of product that has a RRP, but agree, price of a house.).
Original cost of the Alto was $30,000+. Only sold a few thousand units, however the ideas of a graphical user interface (GUI) and a Mouse was picked up by Steve Jobs on a visit in 1979 and adopted (nicked) by Apple into their Lisa computer in '83 and subsequent Machintosh computers.
Bill Gates on the other hand was consulting for IBM and offered to write the Operating System for their pending Personal Computer (PC). In fact he offered $50,000 to Seattle Computer Products for their QDos product and then tweaked it into MS-Dos before licensing it to IBM for their 1981 launch of the IBM XT PC.
With the growth of Apple and their GUI, Microsoft started to develop their own, called Windows in '85, which was an add-on to their text based Operating System, MS-Dos. It probably wasn't till '90 when Windows 3 was launched that PC's powered up direct into a Graphical looking Operating System.
Michael Dell started his PC clone business in '84 running out of a Condo with a handful of employees in Texas. Like Alan Sugar with Amstrad, the computers were sold direct to the end user. In '87 Michael launched his UK business.
By '92 he was the youngest CEO of a Fortune 500 company. In '96 Dell starts selling servers, expanding into the Enterprise market. He's reported to be worth over $50 Billion.