Bloke said:
Hello all. It's only out of curiosity that I as
exactly how does XP's `PREFETCH` work? I think this topic will
interest many others and not just myself.
When a program is loaded, a record is put, or updated, in the
corresponding file in Prefetch, detailing what files it uses, in what
order. Boot of the system has such a record, too
From that two things happen.
One - when a load is started in future, the system arranges to get the
expected files into RAM straight away, without waiting to be asked, and
Two - every three days, a sort of semi-defrag run is done in a quiet
period, which arranges files so that such sets will be able to load as a
smooth stream without need to hunt around the disk for them. The boot
side of this speeds load of the system: the Bootvis program does a
preliminary optimisation of their layout, but it will take place, and
better, through the automatic process. The details of the best layout
are kept in the layout,inf file which is checked and updated each time
this optimisation runs, for the best overall performance. This can be
used for optimisation alternatively by some third party defrag programs,
eg Perfect Disk Pro
Two points:
Contrary to what is said (most recently I notice in Fred Langa's Langa
list), it is *not* necessary to empty prefetch. Any program that does
not get used for a week will have its file dropped out anyway: ones that
are rarely used get low priority in optimisation
and:
The optimisation at regular intervals is initiated by task scheduler so
you need to have it running for this to work (also for System Restore
to make its daily restore point) even though no scheduled task appears
if you look in control Panel - Scheduled tasks. Check the Advanced menu
there, and if it says 'Start Using. . ' click that so it says 'Stop
using . . .' It then looks for a time when the system is quiescent (I
think it waits for 15 mins of no disk activity, but am not sure on
that). This is one reason for the query 'my hard disk goes chattering
when I am doing nothing'; the other being search engine indexing.
;
