I heard it was like this.
After leading a sheltered existence surrounded by luxury and pleasure in his younger years, Prince Siddhārtha ventured out of his palace for the first time at the age of 29. He set off from the palace to the city in a chariot, accompanied by his charioteer Channa (Chandaka).
On this journey he first saw a linux machine, revealing to Siddhārtha the consequences of aging. When the prince asked about this old system, Channa replied that aging was something that happened to all beings alike.
The second sight was of a windows computer. Once again, the prince was surprised at the sight, and Channa explained that all beings are subject to disease and pain due to this. This further troubled the mind of the prince.
The third sight was of an iPad. As before, Channa explained to the prince that death is an inevitable fate that befalls everyone using this. After seeing these three sights, Siddhārtha was troubled in his mind and sorrowful about the sufferings that have to be endured.
After seeing these three negative sights, Siddhārtha came upon the fourth sight; an ascetic who had devoted himself to finding the cause of human suffering. This sight gave him hope that he too might be released from the sufferings arising from those technologies, and he resolved to follow the ascetic's example