Nationally [ 2009-2010], about 21% are business majors, 10% major in social sciences and history, 8% in “health professions and related programs”, 7% are educational majors, 6% psych majors, 5% in visual and performing arts, 5% in biological and biomedical sciences, 5% in “communication, journalism, and related programs”, 4% in engineering, 3% English and literature, 2% in computer and information sciences, 1.4% in physical sciences, 1% in mathematics and statistics. I haven’t mentioned everything.
Harvard  is different. They had 758 kids majoring in economics, 495 in government, 306 in social studies, 290 in psychology, 247 in English, 236 in history, 158 in history and literature, 155 in neurobiology, 154 in molecular cell biology, 154 in sociology, and so forth.
This was back before highly engineered laptops, when PCs were simply big metal boxes with lots of slots in them, so assembling the 100 (or so) parts didn't require any impressive machine tools. Lots of hobbyists assembled their own PCs in those days. (There were opportunities for hot rodding PCs in those days. For example, I got an early IBM PC AT. The CPU's clock speed was set at 6 megahertz, but I ordered a part that made it run at 8 megahertz and enjoyed 33% faster speeds.)
I was an unusual student in that I went directly from undergraduate to MBA school in 1980. Something I noticed was that at age 21-23 I enjoyed the MBA school topics more than the undergrad topics because they felt more age-appropriate. As an undergrad econ major, I was supposed to worry about things like: What should the Fed do now? I had lots of opinions on the Fed, but I never felt like the Fed was on the verge of calling me up and asking me for advice, much less paying me money to tell them what to do. In B-School, however, we talked about case studies like: should a pet foods company bring out a line of gourmet refrigerated dog foods for the luxury market? * That seemed like the kind of topic that a company might plausibly pay me money in the next few years to advise them upon.
* In case you are wondering about gourmet refrigerated dog foods, a little poking around on the Internet shows they they were not successful back in my day, but have over the last few years become an established category. I suspect a necessary condition was the development of stand-alone pet food stores and/or small, cheap refrigerators that are now ubiquitous in retail outlets, typically for soda pop. The big problem I noticed in 1981 with the idea (besides the obvious questions about whether it's stupid and does your dog really care?) was that supermarkets would be reluctant to stock dog food in with refrigerated human food, while pet food aisles in supermarkets didn't have refrigerators.