By Mark Ward
Technology correspondent, BBC News website
If ever there was a company built to reflect the personality of one of its founders, that company is Microsoft.
The basic character of the firm was established as long ago as 1976 when Bill Gates clashed with the members of California's legendary Homebrew Computer Club.
This was where many of those that have gone on to shape the hi-tech world first met and chatted about their new hobby and the first popular home computer - the Altair 8800.
Bill Gates and co-founder Paul Allen wrote software for the Altair that actually allowed hobbyists to do something with it.
Homebrew members seized on the software, copied it and freely distributed it - much to Bill Gates' annoyance.
In an open letter to the group Mr Gates decried this willingness to steal.
All that copying without paying does, he said, "is prevent good software from being written."
"Who can afford to do professional work for nothing?" he asked in the letter, signing himself as a general partner at Micro-Soft.
Protect and survive
The letter is widely seen as establishing Microsoft's basic outlook as a fierce protector of its own programs. It stands in stark opposition to a more open approach that lets anyone tinker with the innards of software.
And, because Paul Allen stepped down from Microsoft in 1983, the letter is also seen as an insight into Bill Gates business philosophy.
That protective ethic carried over to operating systems such as DOS and the various incarnations of Windows and defined Microsoft's technical and business strategy. For a long time it was a great source of strength for the company.
It helped Microsoft gain control of the market for desktop computers and meant that innovation only happened when it said it could - largely because Microsoft controlled who had access to the way its software worked.
It is something of a myth that Microsoft is an innovator. The majority of the novelties in the computer world (including using windows as an interface, the spreadsheet and web browser) that we use on PCs today were invented outside Microsoft.
Microsoft has been keen to protect access to Windows
And, as many commentators have pointed out, Bill Gates' dedication to Windows has been a brake on the risks the company has been willling to take.
The rise of the internet and the open source and free software movement has made that desire to protect Windows and use it as the foundation for everything Microsoft does more of a weakness.
This is because the centre of the computer world has shifted from the desktop to the network - specifically the internet. Which is something Bill Gates has admitted he did not see coming.
Famously, Mr Gates engineered a u-turn at Microsoft in 1995 when he belatedly tried to catch up with net start-ups that were showing it a clean pair of heels. At the time tens of millions of people were browsing the web without any help from Microsoft software. The Internet Explorer browser had yet to make an appearance.
It is one of the ironies of hi-tech history that just as Bill Gates broadly succeeded in his aim of putting Windows on every desktop it no longer mattered.
The net, by its nature and founding ethic, encourages a more open and collaborative style of use and software development.
The success of this approach can be seen in the open source Apache software which is used on more than 60% of web servers. By contrast Microsoft's rival product, IIS, barely tops 30%.
It is also interesting that Google, one of Microsoft's most serious rivals, runs the many thousands of computers in its global network of data centres using Linux - an open source operating system.
Microsoft has admitted it was late to spot the threat from the net
At the same time, people are less and less interested in sitting down in front of the same PC and more interested in getting at their stuff no matter where they are.
This does not just apply to consumers keen to read e-mail on their phones as well as their laptops or PCs. It also applies to businesses many of which are starting to use net-based software services rather than buy, install, customise and maintain programs themselves.
Companies such as Salesforce.com and Qualys are among the leading lights of this software-as-a-service movement.
Plus in recent years Microsoft has innovated often by acquisition rather than by building technology in-house.
So it is probably appropriate that Bill Gates is passing his role as chief software architect to Ray Ozzie - whose signature work was on software called Lotus Notes which helps people collaborate across a network.
In many respects Bill Gates is an icon of an earlier era and Mr Ozzie is one of the standard bearers of that more open way of working.
And, it has to be asked, if Windows and Bill Gates' are so tightly coupled, if one goes, will the other? Could Windows Vista be the last outing for the operating system?
Clearly Ray Ozzie has some tough decisions ahead.