Ok, you have talked about things like Unix, OS/2 and Windows NT, but what about DOS and MS-Windows?
Well, here things get a lot grayer. First, older versions of DOS have notoriously bad disk cache programs. Since neither DOS nor MS-Windows are preemptive multi-tasking systems, it is much harder to do read ahead. Also, since DOS/MS-Windows users are used to being able to power off their computers at any time, doing write behind is much more dangerous. DOS and MS-Windows also can crash much easier than these other OS’s, so people might reboot for many reasons. Caching controllers usually leave the hard disk light on when they have data that hasn’t been written out, and people don’t usually power their computer off until that light goes out. This lets the controllers do write behind fairly safely. (But you can still loose power, so this isn’t risk free.) They also do crude read a heads by prereading entire tracks. DOS also runs in real mode and real mode can only access 640K of memory. This mean that a disk cache can be real helpful. Unfortunately, to do a software based disk cache, the
