Rackmount effects are made for mounting into a rack. A rack is a box (or shelf) with rails 19 inches apart. Rackmount devices can be securely screwed into the rack.
Rackmount effects units do all the same things as effects pedals do only they are packaged differently.
A rack-mounted box is useful for effects like compressors or EQ that you don’t need to change much during performance. They are also useful for effects that need more room to house larger components such as tubes.
Many times rackmount gear has a better interface for controlling an effect’s parameters. There’s more room for knobs and switches than on a small pedal.
Multi-Effects and Dedicated Effects
Similar to bass effects pedals, rackmount effects can contain multi-effects (many different types of effects), or one dedicated effect. The same ideas apply as for effects pedals. Dedicated effects tend to perform their jobs very well.
It’s important to note how hot your rackmount gear gets over the course of running for a few hours at a time. Make sure your rack is well-ventilated so your gear doesn’t overheat and malfunction.