Some say that asking IBM to fess up about how many once-upon-a-time OS/400 shops have migrated to a different platform is like asking a poker player to reveal the cards in his hand: It just ain't gonna happen.

But all bets aside, some folks nearest to the customers (mainly software vendors selling the tools to convert applications and also analysts in the field) speculate that shops are migrating to and away from the i family of servers while others are modernizing. They just can't identify how many are taking each path. Money doesn't seem to be the deciding factor although there isn't any information available to show whether it's more cost-effective to convert OS/400 applications to another platform or to modernize them.

One study done several years ago by Forrester Research estimated the cost of migrating code from an iSeries to a Unix or Linux system at $20 per line.

But it isn't that easy, says Brad Day, a vice president and senior analyst at Forrester Research. "You can't say what is the cost to migrate from one platform to another," he says. "It's much more complicated than that."

IBM converts customers between its own platforms and from other platforms to its systems, but the company doesn't discuss the cost because it varies so much between cases. IBM won't even offer up a range, an IBM spokesperson says.

Usually what affects the number of poker chips it takes to migrate to a new platform is how extensive the migration is. For example, it would cost more to move a system to a dissimilar version of a completely different operating system and database than to migrate applications between similar operating systems, such as moving DB2 on Linux from a p5 to an i5 machine. "The cost is in services," Day says. "It's a per-diem-billable exercise."

One thing's clear when determining whether it's best to stay on the i or go with another platform: It's usually an application-led decision, Day says. "It comes down to what makes the best sense for the application the business wants to run," he adds.

For i5, that's a good thing. "It's the only platform that can support many operating systems," Day says. "No other platform can do as many operating systems as it can in support of applications."

So when companies consider the future, they might end up choosing an i5, Day says. Because most businesses aren't certain what applications they might need to add as their business grows, they might go with an i5 because it can operate applications on the top platforms for software: Windows, AIX, Linux, and i5/OS. "There might be a killer app they can run that they haven't found yet, and they know it would first end up on one of those platforms," Day says.

There are other arguments for going with an i5, including the lower lifecycle costs that result from minimal staffing. "A manager running an i5 shop is often the system administrator, system operator, and database manager all in one," Day says. "IBM made it so turnkey and integrated that one person can manage what normally would require multiple IT staff on other platforms."

Costs aren't the deciding factor in a shop's decision whether to modernize or migrate an OS/400 system, says John Ball, vice president of marketing for iSeries development tools vendor ASNA, whose product lineup includes software for moving RPG to Windows. He's noticed that software vendors tend to migrate their OS/400 applications to other platforms to achieve growth beyond the iSeries market while mixed-environment enterprises tend to migrate off OS/400 to what they see as the most contemporary system, and small iSeries shops tend to stay put and, perhaps, modernize.

BCD, another tools vendor, advocates modernizing on the iSeries. Eric Figura, the company's director of sales and marketing, thinks most shops view modernization of legacy apps as the strongest option for capitalizing on their investment and creating stable, scalable code.