This article is from the Macintosh system software FAQ, by Elliotte Harold elharo@shock.njit.edu with numerous contributions by others.
If you use System 7.0, 7.0.1, or the System 7.0 printer drivers,
you need System 7 Tuneup 1.1.1. The tuneup includes a number of
fixes and enhancements to System 7, including substantially faster
printer drivers, a StyleWriter driver that supports background
printing, a fix that saves several hundred kilobytes of memory on
non-networked Macs, and, most importantly, a vaccine for the
disappearing folders bug.
<URL:ftp://ftp.support.apple.com/pub/apple_sw_updates/US/Macintosh/System%20Software/Other%20System%20Software/>
If you're using System 7.1, 7.1 Pro or 7.1.2, then you should
install System Update 3.0 instead, available from
<URL:ftp://ftp.support.apple.com/pub/apple_sw_updates/US/Macintosh/System%20Software/Other%20System%20Software/>
This replaces all the various System Software Updates and Hardware System
Updates. None of these are necessary for System 7.5.
If you're using System 7.5 you should install System 7.5 Update 2.0
instead. You can get it from
<URL:ftp://ftp.support.apple.com/pub/apple_sw_updates/US/Macintosh/System/System_7.5_Update_2.0/>
This will bring you to System 7.5.3. Next you should install the
System 7.5.3 Revision 2 update, available from
<URL:ftp://ftp.support.apple.com/pub/apple_sw_updates/US/Macintosh/System/System_7.5.3_Revision_2/>
 
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