Xlr usb/firewire interface?

Im a drummer for a few different rock bands and have spent a lot of time in the studio. I'm currently looking to setup my own studio but have a question on the equipment. I number of the studios I've been in have a single mixer with multiple inputs, then a usb cable from the mixer to the computer. Others have a mixer with a number of inputs and the same number of outputs that go to a box, with a usb or firewire line from the box to the computer. Visually, it appears that the box just takes those inputs and puts them on separate logical pipes inside the usb. The box itself does no mixing or signal processing other than to take the xlr or stereo inputs or whatever and put them on the usb line to the computer. This allows the computer to record each instrument on a separate track in the recording program. When each drum is mic'ed separately, each drum appears on a separate track in the recording program. Does anyone out there know what this type of box is called, who makes them, and where they are available for purchase?