Last October, Electronic Data Systems CEO Ron Rittenmeyer approached Hewlett-Packard CEO Mark Hurd with an idea, people familiar with today’s $13.25 billion deal told Deal Journal: Would Hewlett-Packard be willing to consider something like a joint venture in which the company would sell its services business to EDS and let EDS run it?

Seven months later, the two companies decided on a slightly different plan: Hewlett-Packard is taking over all of EDS, and combining their services businesses into one unit, which will still be known as EDS, run by Rittenmeyer, and based in Plano, Texas. H-P will allow EDS to run essentially as a standalone business, with no tweaks or significant cost cuts.

The trip from a “joint venture” that EDS would control to an all-out acquisition of EDS is a long, twisting one.

To many people — including, possibly, investors who slammed H-P’s stock this morning — H-P’s decision not to integrate all of EDS may be mystifying. The lack of a big integration acts as a warning sign to many: think of Sprint and Nextel, a deal in which Sprint snapped up the deliciously cheap Nextel, maintained two separate headquarters and two different primary technologies, and then allowed internal bickering and competition between the two companies to destroy the entire value of the combination. It is possible that Hewlett-Packard may be feeling the sting from its acquisition of Compaq in 2002, which involved a long integration so problematic that it prompted the ouster of former CEO Carly Fiorina. But that doesn’t seem enough reason not to fold EDS into the company.

Instead, EDS saw in H-P a savior, of sorts. EDS is facing slower revenue growth than H-P is, and its operating margins are lower. EDS management became convinced that H-P would be able to fix and grow the business in a way that it could not grow on its own.

At the same time, H-P needed to expand its services business, especially globally, to compete with IBM. H-P’s services business has a weaker brand name than EDS does, which is why H-P will spare EDS the integration growing pains. And a long integration may also have put H-P behind on its goal to compete with IBM. H-P looked at IBM and saw a business that was working — and IBM draws about 60% of its revenues from services. “H-P realized that IBM has the model right,” one person knowledgeable about the agreement said.