Wikipedia
PerfectDisk is the name of separate but related defragmentation utilities for Windows and HP OpenVMS published by Raxco Software. It has won several awards from computer magazines, and is certified by Microsoft for all its current NTFS-based operating systems. The current version is PerfectDisk 14.0.
PerfectDisk has editions designed for most user categories, from home PCs to large servers and virtualization-aware editions for virtual environments. In addition to defragmenting files, it also optimizes disk drives with an optimization strategy called SMARTPlacement and it prevents fragmentation with the OptiWrite feature. PerfectDisk defragments data and system files and places a high priority on free space consolidation. SSD Optimize is an optimization method for solid state drives that focuses on free space consolidation without defragmentation of files.
The OpenVMS version of PerfectDisk, still in production, predated the Windows version by several years and contributed much of the approach adopted by the Windows versions. It was developed by William Davy and operates on the Files-11 file system used by OpenVMS. It features a single-pass, four-phase algorithm, intelligent placement (moving infrequently-accessed data to the periphery of the disk to reduce average seek distance,) locating directory files near indexf.sys (the Files-11 counterpart to the FAT or MFT) and clustering of "volatile" files, which attempts to make a file deletion more likely to occur adjacent to existing free space. It was the first defragmenter capable of defragmenting an open file that was actively being written, by combining the defragmenter with specialized functionality of Raxco's Data Caching product, PerfectCache, forming a product called UltraDisk.
In the mid-1990s, Raxco assigned several developers to create a Windows version of the defragmenter. Since the original product was written in VAX Macro (assembly language), starting from the existing source code was not a viable solution. Instead, the defragmentation strategy, which was largely applicable to Windows file systems despite coming from a different operating system, was refined and applied to a new code base.
Raxco released PD Free, PerfectDisk Free Defrag, in late March 2012 as an exclusive download at CNET Download.com. PD Free is a fully functional free defrag utility using PerfectDisk's patented features including SMARTPlacement, SSD Optimize, Boot Time Defrag and Quick Defrag as well as scheduling options. As of April 2, 2012, PD Free is available as a free software download on most major download websites.