Some data warehousing platforms offer intergenerational compatibility while others force you to migrate and retire the old stuff. Teradata, for one, has long maintained compatibility between several generations of releases so you can mix old and new hardware to scale up the total environment. If there's no compatibility, the boxes can't be linked to access data as a single environment. Even when compatibility is an option, there are limits to just how many generations of databases and hardware vendors can span, so check with your perspective vendor on compatibility and the long-term upgrade roadmap. Retailing giant Walmart has been a Teradata customer for more than 20 years, and last year it reached an agreement with Teradata to extend the relationship. Teradata powers Walmart's enterprise data warehouse, a data store that analyst Curt Monash pegged at 2.5 petabytes back in 2008. As part of the new agreement, Walmart's Teradata deployment will be expanded and refreshed. Up-to-data hardware usually offers good reason to upgrade. The latest Teradata products are said to use 50% less floor space and 40% less energy than older generations of hardware.