Update installation: on the fly or at shutdown

[Levlg]

I have WinXP with automatic updates.
My system sometimes suggests to install the updates directly on the fly.
But sometimes my system installs the updates at shutdown of the computer.
Why this is done in such a way?
Is this because updates of different type?
Is this because updates of varying urgency?
Is this depends on the work being done on the computer at the time of
updates come?

Thanks
Lev

 

[Colin Barnhorst]

It depends on what is being updated. A system file that is in use will
require the update to complete after a restart because the file cannot be
changed while it is in use. It varies by how the file is used by your
computer.

 

[Levlg]

Thank you for answer!
I understand that there is an update, which must be installed when Windows
is not running. For such updates required restart. But why sometimes require
restarting appears in the work, and sometimes the installation is done when
you turn off the computer?
Lev