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All correct, but even if i manage to double disk performance by freeing space and removing startup programs so that startup time without avast is 1 minute, with avast it would still be 3 minutes. I don't see how doing so would get rid of the big portion introduced by avast.
The greater the number of programs running at startup the greater the activity of the AV will be and this isn't just Avast.
On this XP system the impact of Avast is negligible, but startup is a busy time and the three elements you mentioned - "instup", "aswidsagenta", "AvastSvc" - are part and parcel of the protection.
1. Instup - is the installation and update function and shortly after boot it checks for updates.
2. aswidsagenta - AvastSoftWare IntrusionDetectionSystem Agent, this I believe is related to the Behaviour shield.
3. AvastSvc - Avast SerViCe - the main avast service controlling the various scanning functions.
Whilst I don't believe this will make a great difference you could try this:
AvastUI > Settings > Troubleshooting - enable the 'Load Avast services only after loading other
system services.