A main cause of slow boots with Windows NT/2000 was their method for loading drivers. Prior to XP, Windows versions loaded drivers sequentially. Windows XP, however, loads drivers concurrently. It also records which applications are launched during startup. This information is written to the C:\WINDOWS\Prefetch\Layout.ini file.
When the Layout.ini file is created, XP performs a partial defragmentation on the files listed in Layout.ini. This defrag process attempts to make the files listed in Layout.ini available in one contiguous area on the hard disk, allowing these files to be accessed, and the associated drivers to be loaded, more quickly. This process is run in the background approximately every three days.
BootVis, which Microsoft describes as a “performance trace visualization tool,” actually performs the same tasks as the XP boot process, except that BootVis allows the information obtained during a single boot to be used for optimization, rather than monitoring the system over a period of several days.
Download the file and then extract the BootVis.exe utility by double-clicking the archive file, selecting a location for the Bootvis.exe file, and clicking OK.