My coworkers and I have often wondered this. My own best guess is that it's that classic bugaboo: Historical reasons. They've got a big installed base of hardw

My coworkers and I have often wondered this. My own best guess is that it's that classic bugaboo: Historical reasons. They've got a big installed base of hardware, software, and ops procedures to support 32-bit small and medium instances, and thus the marginal cost of continuing to run that hardware is lower. Given the choice between (a) a big program to compel all their existing 32-bit customers to migrate to 64-bit infrastructure, and then writing off all the racks full of 32-bit equipment; or (b) maintaining and building out the datacenters and infrastructure that they've already got established, they tend to choose option (b). Of course, given that the price of compute hardware continues its inexorable fall, in three years Amazon will offer 64-bit at an intermediate price point: The expensive 64-bit large instance of today will be the cheap 64-bit large instance of tomorrow, and people who want real power will be paying for 32xlarge instances.