He'd dyed his hair, which was almost unheard-of in the 1960s.

他染了头发，这在20世纪60年代是罕见的事。

Being relatively small, the screen had a resolution of a then-unheard-of 200 pixels per inch (ppi).

一款相对较小的显示器，它拥有一个前所未闻的每英寸200像素的显示屏。

He sometimes fires people for simply not doing a good job, “unheard-of in government service,” he wryly notes.

有时候，盖茨会因为部下干得不够好就打发他走人，并在辞退备注里面讽刺地写上“没听说过有这个人”。

Riots are almost unheard of in Japan.

暴乱在日本几乎是闻所未闻的。