This was a question I initially posed to a friend of mine back in high school while we were discussing one of our favorite shared passions, audio equipment. Digital amplifiers were starting to appear on the scene, and I wondered aloud why all the circuitry couldn't be shoved on a single slab of silicon and be done with it. My friend (who knew electronics on that level) said it was theoretically possible, but you wouldn't be able to build an amplifier in the 80-100 watt per channel range we were currently enjoying because of the heat and power constraints. This was the age of "big iron" in audio, after all.
A few years later when I first started getting into personal computing I found myself asking the same question. Why can't all this crap be put on a single chip, or at least on the main system board?
Why did I need separate plug-in cards to control hard drive? Why did I need a separate card to control the I/O functions? Why did I need a separate video card? WHY COULDN'T ALL THIS STUFF BE ON A SINGLE BOARD?
Well, for starters, at the time the technology just wasn't there; we're talking the 8088/286/386 era, after all. The first few computers I owned (built from parts I'd gotten at computer fairs) had banks of discrete memory chips on the system boards and a 20 MEGAbyte drive was considered big! Good luck trying to troubleshoot a bad chip if you ended up with one. That's why I was dancing in the streets when the first DIMMs started to appear. Imagine that: four (or however many) memory chips soldered to little circuit boards that just snapped into the system board!
As the years progressed, I was happy to see that I wasn't the only one who had been wondering why all these discrete items couldn't be made part of the system board, because slowly drive controllers and I/O found their way onto motherboards, and before long, even video was becoming a standard part of the build. You could still buy souped-up peripheral cards, but they were no longer a necessity to build a functioning system.
And now here we are in 2015:
Just look at what Apple's done with the latest MacBook. We still aren't to the point where everything is on a single chip, but we're damn close. That tiny system board not only contains the CPU, memory, and controllers, but also the machine's solid state "hard" drive.
Being the inveterate nerd that I am, I've always taken great pleasure in peeking at the guts inside my tech, and I have to admit, as we get closer and closer to the "everything on one chip" I used to dream about, a part of me is kind of disappointed there isn't a whole lot left to look at when you pop the hood.