Thanks, Clive.
I've just been thinking about why
PIN Number is more used than, for example,
PC Computer, or LCD Displays... Hm... No, people actually say LCD displays! Just discovered another one sample. In case of PIN, the word itself has other meanings, used as a noun or as well as a verb. So adding Number probably clarifies the exact meaning. Thinking about LCD Displays, the only another meaning of LCD that comes to mind is connected to drugs, so it is very unlikely to be confused with an electronic device
![Smile [:)]](/emoticons/emotion-1.gif)
Another idiom? And how about DVD/CD Disk? Used all the time.