关于Vcc和Vdd的差别，以前就一直有这个疑问，后来也有和一个师弟谈到，当时他还想到会不会是和器件的几个端有关，结果我当时没考虑到双极器件，就认为不对，现在想起来才觉得惭愧啊…

下面是google了一番之后的结果：
Apparently this terminology originated in some way from the terminals of each type of transistor, and their common connections in logic circuits (i.e., Vcc is often applied to BJT collectors, Vee to BJT emitters, Vdd to FET drains, and Vss to FET sources).

This notation then carries across to integrated circuits — TTL ICs were originally based on BJT technology, and so often use the Vcc / Vee terminology; CMOS ICs are based on FET technology, and so often use the Vdd / Vss terminology.

The absolute distinctions between these common supply terms has since been blurred by the interchangeable application of TTL and CMOS logic families. Most CMOS (74HC / AC, etc.) IC data sheets now use Vcc and Gnd to designate the positive and negative supply pins.