There have been a number of articles recently about Microsoft and Apple. While both companies are well known brands, most comparisons miss the fact that they are completely different businesses.

This history of IBM, Microsoft, and Apple also tells the tale of the "personal" computer.

Once upon a time computers were room-size mainframes, all computers were used for business and THE business computer company was IBM. IBM was serious business.

In the 1980s tiny startups appeared trying to create “personal” computers, maybe even put a computer on every desk. This was heresy to Big Blue but IBM was powerless to stop it and eventually even they got in the act with the IBM PC. The world of computing profoundly changed.

Fast forward 30 years and everything has changed again.

IBM still makes mainframes computers but their visibility has been greatly diminished as business focus has moved from the back-office to the desktop. IBM eventually gave up on desktop computers altogether and re-invented itself as a "services" or consulting business.

Microsoft has changed too. It has replaced IBM as THE business computer company. Business computing has shifted from mainframes to desktops and Microsoft makes the OS and the productivity software that runs business globally. Once the champion of "personal computers", Microsoft’s focus has changed from the personal computer to “enterprise software”.

And then there is Apple. Apple was the David to IBM's Goliath in the 1980's, pushing hard for personal computers. For decades it quietly made desktop computers that felt more personal, the PC for the rest of us so to speak. In the 1990's, Apple tried to get into serious business and floundered badly. The company almost went out of business but its loyal following kept it alive churning out desktop computers. Then CEO Steve Jobs returned to the company and things started to change. A lot.

It wasn't obvious at the time but it is now. Apple has reinvented the idea of a "personal" computer by taking the idea to the next level. It is not about a computer in every desktop anymore; We have that.

The next stage of personal computing is a computer in every pocket or backpack. Apple has emerged as the company pushing this vision harder and more successfully than anyone else.

It is pretty amazing how much Apple has changed in the last 5-10 years. As proof, look at their income statements and you will see a desktop computer company that has reinvented itself as a portable computer company. Apple built a solid, extendable foundation with MacOS X on the desktop and then they expanded: first laptops, then iPods, then the iPhone and now the iPad.

Apple still makes a tidy profit with desktop computers and they sell more Macs then ever before but after less than 3 years, 40% of their revenue (40%!!) comes from the iPhone alone. Add in iPods and iPads and one can see the future. Apple is now a mobile computing company. With iPhones selling in Wal-Mart? You can expect that trend to continue.

This transformation is also why Apple’s stock price has taken off and Microsoft’s has cratered. Enterprise software is for business and every business has a copy (legal or otherwise) of some version of Office and Windows. Enterprise software is a mature business which is driven by upgrades not new customers.

Almost everyone that can afford a desktop computer already has one but how many people have a pocket computer? If every person buys a smartphone and every other person buys a tablet, Apple stands to make a lot of sales to brand new customers. These are growth businesses not mature businesses and Apple products have emerged as "affordable luxury" items in these markets. Apple's devices are aspirational in segments that represent enormous future sales opportunity. The stock prices reflect that.

While Apple, Microsoft and IBM are often compared and have a shared history, they are different creatures today. IBM was mainframes and became services. Microsoft was personal desktop PC's and became enterprise software on the desktop. Apple continues its journey as the "personal computer for the rest of us" as an emerging mobile computing company.

And the story continues. How will things look in another twenty years?