How do these Mobile Rack systems work?

I see a lot of rack systems that seem to be made for some type of cases system that allows you to have multiple dives connected to your computer. I am guessing that these would allow me to have drives in an external case with its own power supply and connect it to my computer. I must have something wrong in my guess. I see a lot of $10 racks but I have yet to see any case system.

Is there some way that I can build a case outside of my main system that will hold multiple 3.5 and 5.25 inch drives where I can swap out drives using these racks?

Thanks in advance. Here is a link to some of what I se.

The whole idea of mobile racks is simple. It’s removable storage.
Instead of mounting an internal drive which is permanent, you could use mobile racks which allows you to make swap outs without fuss.
The applications are varied. If you look at my signature you will see that I run several Operating Systems. I do not like to dual boot. I prefer the clean isolation so I use a different hard drive mounted in a mobile rack. This allows me to swap out the racks depending on which Operating System I choose to run.

The rack comes in two pieces. A frame which is permanently mounted in the PC and a tray (contains the hard drive) which is inserted and removed from the frame. The trays can be purchased seperately, thus the $10 price tags you may encounter.

Variations in price reflect varied features such as size, cooling, construction, speed (ATA100/133 5400/7200RPM), interface (PATA/SATA, SCSI), hot swappable (OS supported), etc,.

Nemesys, thanks for your input. It looks as though they will not solve my needs for an outboard box that will hold multiple 5.25 inch drives. I’ll just have to stack a bunch of external enclosures.

I appreciate your time.