In such cases, all you need are the basics. Some Apple II models require interface cards for connecting disk drives or certain monitors. You can also try searching the Internet for better bargains, starting at comp.sys.apple2.marketplace . So with just the basics you can play your favorite games and run many software titles on disk. Well, if you want to do any of these things and more, you'll need to have an operating system.
Some OSs can fit on a single disk, however, others require a hard drive.
This will run on almost any Apple II, including the first. There are many older programs available for DOS 3.3. This was Apple's replacement for DOS 3.3. Any Apple II with enough memory can run earlier versions of ProDOS, however, to use ProDOS 2.0 and beyond you will need an enhanced Apple IIe or better unless you add extra hardware to your system. When you start up your IIgs, it will display the ROM version, if it does not, then it is a ROM 00.