Microsoft's plan to run Exchange 12 only on 64-bit platforms is a mistake, an analyst said Monday.

"This was not a good move on Microsoft's part," said Peter Pawlack, analyst with Directions on Microsoft, a Redmond, Wash.-based research firm that specializes in tracking the developer.

"Sixty-four bit is definitely coming on, and as people move forward to new systems, they'll buy 64-bit servers," said Pawlack. "But we're not there yet. I think upgrades and migrations [to Exchange 12] are going to be very slow."

Last week, Microsoft announced that Exchange 12 -- which should release sometime in the first half of 2007 -- will be exclusively 64-bit. By Microsoft's account, it made the decision because of the performance gains that 64-bit offered over 32-bit.

"The product team have been testing E12 on 32-bit and 64-bit, and have found some significant gains and a reduction of IOs per second which results in really good performance gains," wrote Eileen Brown, a Microsoft IT evangelist, on her blog. "They tested Exchange on 64 bit and found almost a 75 percent reduction in IOs per second compared with Exchange 2003. This could result in almost a 4X increase in the number of users on the same disks or require 1/4 the disks to support the same users."

Pawlack and his colleagues at Directions saw it differently.

"It's a move made not on technical merit, but because Exchange is running into scheduling problems. It was done to reduce the test matrix and help move the schedule forward. We feel that's the only rational reason for doing this."

Microsoft is pushing 64-bit Exchange even though it's promised to support a 32-bit version of its next-generation server software -- Windows Server 'Longhorn' -- until 2017.