If you're talking about the sharp decline in computer science degrees granted to women around 1984, I have a couple of guesses.

First, no one really knew what kind of career path getting a computer science degree entailed until around then anyway, and once women had figured it out they decided they didn't want it.

Second, in my opinion women are much more sensitive to their career's stability and predictability than men are, for the simple reason that they're the ones who have to plan out when to have children. You'll notice that the drop-off more or less coincided with the first (or second, or maybe third - I forget which) big bust in the PC industry in the 80s. Mainframes and even microcomputers did not have boom-and-bust cycles like PCs did in the 80s, although individual companies might blow up the industry as a whole was relatively stable. College students looking for stability around that time might sensibly decide "computing" wasn't for them any more.

My favorite reference in this discussion (well, about women in science and engineering as a whole) is Philip Greenspun's article (http://philip.greenspun.com/careers/women-in-science) who basically makes the argument that the median scientist who doesn't win Noble Prizes actually has a pretty crappy career and that women are smart enough to stay away.