Predicting the future is notoriously difficult.
Who could have imagined, in the mid 1970s, for example, that by the end of the 20th century, computers would be as common in people's homes as TV sets? In the 1970s, computers were common enough, but only in big business, government departments, and large organizations. These were the so-called mainframe machines. Mainframe computers were very large indeed, often occupying whole air-conditioned rooms, employing full-time technicians and run on specially-written software. Though these large machines still exist, many of their functions have been taken over by small powerful personal computers, commonly known as PCs. In 1975, a primitive machine called the Altair, was launched in the USA. It can properly be described as the first 'home computer' and it pointed the way to the future.

众所周知，预测未来是非常困难的。
举个例子吧，在20世纪70年代中叶又有谁能想得到在20世纪末的时候，家庭用的计算机会像电视机一样普遍？ 在70年代，计算机已经相当普及了，但只用在大公司。 政府部门和大的组织之中，它们被称为主机。 计算机主机确实很大，常常占据了装有空调的多间房间， 雇用专职的技师，而且得用专门编写的软件才能运行。 虽然这种大计算机仍然存在，但它们的许多功能已被体积小但功能齐全的个人电脑――即我们常说的PC机――所代替了。 1975年，美国推出了一台被称为“牛郎星”的原始机型。 严格地说起来，它可以被称为第一台“家用电脑”，而且它也指了今后的方向。