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While the basics of the Hotmail system have endured over time, a great deal has changed. One of the huge challenges of running a service like Hotmail is that when we do make changes, we have to make sure that we keep the service running even while those changes are being made. It’s perhaps a bit dramatic, but I like the analogy of changing the engine of a plane that is in flight! We’ve gotten very good at making these kinds of changes and we’re able to make them quite often.
Two of the biggest changes that have been made involve (you guessed it) the Frontend and Backend sub-systems.
Starting in 2004, the Hotmail engineering team completely rewrote the Backend system, moving it off of an expensive and dedicated Unix-based storage system and onto a system that uses Windows Server and SQL Server to exploit inexpensive, commodity computers and disk drives so we can provide users with far greater storage limits than had ever before been possible. The scope of these changes was immense – we had to physically change the hardware in the data centers to new hardware running new software, and we had to move the data from the old system to the new system with no interruption of service to our customers. Of course, this didn’t happen overnight. It was a complex project that took years to complete because of the physical limitations for how quickly we could copy data onto the new disk drives.