When do Delete Old Prefetch files, auto-rebuild, and layout.ini...?

Usually a couple of days after my Windows manual Update there are 31... old prefetch files to delete, and in-between varies...

1. Following deletion, when does Win7 start auto-rebuilding them..., and how long does that usually take?

I read that's at Win idle, And I should probably temp disable my KIS AV's idle scan?

2. Is it also a good idea to manually delete layout.ini once-in-a Great while, and when?

if im not mistaken, if you delete prefetch, it will rebuild the next startup

no need to delete prefetch because it will auto delete and auto rebuild

as you start a program, Windows adds it to Prefetch (if it's not already there, is of a higher version and meets the caching requirements).

so deleting the entries in Prefetch will actually make some things run ever so slightly slower until they get re-prefetched.

it doesn't hurt to erase Prefetch as some programs may be in there that are no longer used or installed - but they will eventually work their way out of the list.

(from memory, only about 130 files are kept, give or take) (ps: that was for XP, I just checked my Win8 and there are 240 but there's a lot of same entries with different versions)

apologies @dvdbane for re-posting your suggestion, I thought it needed further explaining as I wasn't sure of the OP's knowledge of the background to it all.

EDIT: (forgot question 2)

as to layout.ini - personally I've deleted it and the whole Prefetch folder sometimes, back in the XP days, with no ill-effects.

but I stopped doing that action years ago. wasn't much point. all the files get rebuilt eventually, the space saving was marginal at best and there was no reason speed-wise to do it.

the main reason was for when a virus was found and it got Prefetched - then I would blow away the whole folder.

but to answer that question, since the layout.ini file contains entries to system locations/files, unless you know the consequences, leave it alone in my opinion.

it's a harmless .ini file, taking little space (mine is currently 1.5mb) and will get rebuilt anyway.

you would need to have a good reason that out ways the greater potential for things going pear-shaped.

as you start a program, Windows adds it to Prefetch (if it's not already there, is of a higher version and meets the caching requirements).

so deleting the entries in Prefetch will actually make some things run ever so slightly slower until they get re-prefetched.

it doesn't hurt to erase Prefetch as some programs may be in there that are no longer used or installed - but they will eventually work their way out of the list.

(from memory, only about 130 files are kept, give or take) (ps: that was for XP, I just checked my Win8 and there are 240 but there's a lot of same entries with different versions)

apologies @dvdbane for re-posting your suggestion, I thought it needed further explaining as I wasn't sure of the OP's knowledge of the background to it all.

EDIT: (forgot question 2)

as to layout.ini - personally I've deleted it and the whole Prefetch folder sometimes, back in the XP days, with no ill-effects.

but I stopped doing that action years ago. wasn't much point. all the files get rebuilt eventually, the space saving was marginal at best and there was no reason speed-wise to do it.

the main reason was for when a virus was found and it got Prefetched - then I would blow away the whole folder.

but to answer that question, since the layout.ini file contains entries to system locations/files, unless you know the consequences, leave it alone in my opinion.

it's a harmless .ini file, taking little space (mine is currently 1.5mb) and will get rebuilt anyway.

you would need to have a good reason that out ways the greater potential for things going pear-shaped.

Thank you for the reply, and I'm going to stop deleting old prefetch files because of issues... (I got into this habit in the old XP days)!-

2 days after this weeks Win Update- CCleaner deleted 26 old prefetch files (many System prefetch, along with 128mb of deleted files...).

I closely watched the Prefetch folder for rebuild dates/times?

Many didn't auto-rebuild until Late After the next days cold startup/2 restarts.

Performance became slow, and there is still No increase the 2nd day (today).

I also figured that there was No reason to defrag , until All the prefetch files were auto-rebuilt (compact/contiguous...).

BTW- My Win7 64-bit laptop has Really slowed down, after doing similar...

It seems that I sometimes make things worse while trying to make things a little better (i.e. JV PowerTools- Immunize...!).

I going to try and remember!- If it ain't broke, don't fix it! :o