In the 80s, Apple was dominant in the GUI space. Windows 3.1 put a huge dent in this. By the time Windows 95 came out, Apple was essentially dead.
During all this, Intel and Microsoft had an uneasy marriage of convenience. They were dependent on each other but had clear lines of separation between hardware and software.
Microsoft tried to branch out. The original versions of NT ran on other architectures, like Alpha and MIPS. Under Steve Jobs (many may remember that Steve Jobs was only interim CEO for years after the NeXT purchase while the Apple board searched for a replacement for Gil Amelio).
5+ years ago, with a resurgent Apple in the PC space, Apple abandoned Motorla for Intel, killing the PowerPC in all but name. Microsoft had long since abandoned all the non-x86 architectures.
Intel was so dominant that they sold their low-power chip division (XScale) and seemed to have an answer for low cost computer devices in the form of the Atom as the netbook market just exploded.
Intel basically discounted any device smaller than this. So did Microsoft. Apple completely transformed the mobile space with the iPhone and then the iPad, catapulting ARM from a niche embedded product to something eating away at Intel from the bottom end, potentially threatening their entire business.
In the 90s the churn of forced obsolescence made MS and Intel a lot of money and solved a lot of problems. There were no old versions of Windows to support as the market for PCs was growing at a huge rate and hardware just didn't last that long.
Now the CPU power that the average user needs has plateaued. Any PC made in the last 5 years (maybe longer) will be fine for most people. The trend now is towards lower power and more mobility, which is why ARM is a strategic threat to Intel.
It's incredibly funny ("the ironing is delicious" as Bart would say) that Apple is now one of Intel's biggest customers while being the driver to the threat to Intel.
And now Microsoft, once an unstoppable juggernaut, just doesn't get it when Ballmer describes tablets as "just another form factor". They failed for 10 years to make tablets just another way to sell more Windows licenses. They're still kicking that dead horse with Windows 8.
All the while Apple is making money hand over fist and HP, Dell, etc are struggling to make a buck or, in HP's case, getting out of the PC business entirely.
All of these companies try to imitate Apple releasing vaguely copycat products but none of them get it. They're engaged in what I call "shotgun marketing" as they have no idea what the market wants and just fire off a shotgun blast, hoping something will stick.
Only Apple seems willing or able to put the consumer first. The Apple-haters will I'm sure violently disagree with some or all of this.
Microsoft I believe will continue a very long but now inevitable slide into irrelevance (companies that large take many years to die). The jury is still out on Intel.
The only companies that seem to have a long future ahead of them are Apple, Google and maybe Facebook.