Are third-party hard disks compatible with System 7?

Yes. Virtually all of the third-party hard disks tested by Apple are compatible with System 7.

However, you may run into issues if your hard disk driver software (also called formatting software) is out of date. Most hard disk vendors revised their formatting software for System 7. Alternatively, you may try a third-party driver utility like Silverlining or Drive 7. Apple's utility, HD SC Setup, works only with Apple hard disks. Version 7.0 of HD SC Setup comes with System 7.

If you have a question about a specific third-party hard disk or driver version, contact the vendor.