All sorts

Manuals for vintage computers:  https://oldcrap.org

Apple

Apple Archives: http://www.applearchives.com
Apple II Disk Drive Cleaning: Youtube: Apple II Disk Drive Cleaning – YouTube.webloc

Macintosh

Info on your Mac based on the serial number consisting of 11 or 12 characters (before April 2021):

http://www.everymac.com/ultimate-mac-lookup

http://www.appleserialnumberinfo.com/Desktop/index.php

Sad Mac Error Codes: 

https://members.tripod.com/elfen_magix/sadcodes.html

https://tinkerdifferent.com/resources/sad-mac-error-codes.82/

Mac OS 2 – 6 disk images: http://earlymacintosh.org/disk_images.html

Macintosh before System 7: http://earlymacintosh.org/index.html