Randy Mott doesn't think small. As CIO of four of the largest U.S. companies during his career of more than 30 years, he has tended to go "all in" on IT measures, whether they're data center consolidations or workforce overhauls.

But three of those market-leading companies--Wal-Mart, Hewlett-Packard, and now General Motors--couldn't be more different. At least Mott caught them at very different stages in their evolution.

Mott's 22 years at Wal-Mart, where he was CIO from 1994 to 2000, were marked by tremendous growth, as it shot past $100 billion in revenue to become one of the largest corporations on the planet. During those years, as it emerged from the larger-than-life shadow of founder Sam Walton, Wal-Mart was a pioneer in analyzing big data (before the term existed) to optimize its global supply chain and ultimately deliver all manner of products to customers at "everyday low prices."

They were Wal-Mart's glory years, before the lawyers and interest groups and politicians started sinking their teeth into the country's largest employer, and before Target, Costco, Amazon, and other rivals cut in with their own supply chain and business model innovations. It was at Wal-Mart that Mott learned the virtues of delivering IT projects quickly ("speed merchant," InformationWeek called him in a 1996 magazine cover story), and always on a tight budget. It was also where Mott learned to measure everything and to act like a "retailer first, technologist second," a primal business focus he retains to this day.

Mott's HP years, from 2005 to 2011 (following five years at rival Dell), were marked by massive cost cutting and consolidation, as CEO Mark Hurd tapped him to reduce the company's IT spending from 4% of revenue to 2%. Under the Mott-led IT "transformation" at HP (which he took on the road to show off the HP dog food the IT organization was eating), the company modernized and consolidated data centers and applications, moved toward a single enterprise data warehouse, shifted work from IT outsourcers and other contractors to employees, and directed those employees to spend more of their time on new development and less on support and maintenance. Financially rigorous cost-benefit analyses of every IT project, big and small, were the mandate.

Those all-in moves weren't always popular with the rank and file. Unlike Wal-Mart during the Mott years, HP was already a mature company with an HP-Way-or-the-highway culture. It had become the largest IT vendor in the world, largely through acquisitions, but its biggest products and fattest profit margins were under siege. After the HP board ousted Hurd in 2010 for what amounted to technicalities and bad judgment, Mott didn't last much longer under Hurd's replacement, Léo Apotheker, who months later was replaced by Meg Whitman.

HP's day of reckoning is still to come. Even after the company said in May that it will cut 27,000 jobs--8% of its workforce--over the next couple of years amid slumping profits, there's still a sense that things will get worse at HP before they get better.

Out of the frying pan, into the pressure cooker, Mott began his career at GM 20 weeks ago. A historic bankruptcy filing, controversial government bailout, and several years of austerity measures should have knocked most of the arrogance and complacency out of the company's 200,000 employees.

In many respects, GM's a better venue than HP was for Mott to apply his IT transformation/consolidation/measurement playbook. Unlike HP, GM isn't looking to slash IT costs in the process, and by reversing the company's overwhelming reliance on outsourcers, Mott will need to hire thousands of people as it brings software development and other skills in-house.

The way Mott sees it, he's joining a "$150 billion startup," fresh from an IPO (the U.S. Treasury Department still owns 26% of GM) and an executive management overhaul (GM is on its third CEO in 2-1/2 years). Asked why he'd join a company in GM's straits, in an industry where he has no experience, Mott said there are only a handful of multinational companies out there "with an appetite to really change," and he's getting a charge out of learning the IT challenges that come with global auto platforms, just-in-time delivery, and CAFE standards.

Mott knows those challenges are daunting: "You come in and you have a choice to make that says: Does that company deserve the best IT it can get? And with that come hard choices. And they aren't hard choices I necessarily like to make any more than the next human being."

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