Microsoft and Apple's decision to sign a five-year deal that guarantees Office for Mac wasn't just a cosmetic arrangement - it's meant as a clear signal of the depth of the commitment between the two firms.

Scott Erickson, director of product management and marketing for Microsoft's Mac Business Unit, told Macworld why it was necessary: "The commitment came about because we had a lot of questions from people in the Mac community about our commitment to upgrading our software due to the Intel switch," he explained.

"They were asking whether we were going to be in it for the long term. Well, the answer is "yes". Apple knows that and we know that, but we wanted to make a visual and verbal statement to our customers around the world to say 'we are here and we are going to do this'."

The agreement is in three parts, explained Erickson. Microsoft has agreed to continue to develop Office for the Mac with universal binaries for both the PowerPC and the new Intel based Mac, and Apple has agreed to continue to make new technologies available to Microsoft in a timely fashion.

In effect the deal formalises existing relationships between the two companies.

"We think it's a very visual way to represent to customers that we are committed to the Mac, we've been in it for over 20 years and we don't have any plans to go away," he revealed.

The agreement was signed in November 2005 and followed the end of a prior technology agreement between Apple and Microsoft that was signed back in 1997 and expired in August 2002.

Microsoft has also confirmed it will introduce a series of slight upgrades to its Mac products in the current quarter.