I believe most of us do observe this when booting system. Applications like yahoo messenger, dial up connection, etc will automatically open and therefore slow the system. You can disable some programs with this simple tutorial
Step 1
Click the Start Menu Orb then in the search box Type msconfig and Press Enter or Click the msconfig.exe program link.
launch msconfig.exe from the start menu in windows 7
Step 2
From within the System Configuration tool, Click Startup tab and then Uncheck the program boxes that you would like to prevent from starting when Windows starts. Click OK to save changes when you are done.
manually select which programs you would like to disable from auto-start
Step 3
Now that you’ve saved changes Restart Windows and the selected programs should no longer automatically start up.
or
Look in these folders:
C:\Users\\AppData\Roaming\Microsoft\Windows\Start Menu
C:\ProgramData\Microsoft\Windows\Start Menu
Un-check undesired programs in Start > Search > Msconfig > Startup .