"In this blog, we focus on disk defragmentation in Windows 7. Before we discuss the changes introduced in Windows 7, let's chat a bit about what fragmentation is, and its applicability.
Within the storage and memory hierarchy comprising the hardware pipeline between the hard disk and CPU, hard disks are relatively slower and have relatively higher latency. Read/write times from and to a hard disk are measured in milliseconds (typically, 2-5 ms) – which sounds quite fast until compared to a 2GHz CPU that can compute data in less than 10 nanoseconds (on average), once the data is in the L1 memory cache of the processor.
This performance gap has only been increasing over the past 2 decades – the figures below are noteworthy."