This term references the peak of mainframe technology when all of the institution's computer resources were centralized into a single computer room, staffed by technicians in white lab coats. These centers usually had a glass wall where visitors could marvel at the impressive array of flashing lights, spinning tape drives, and row upon row of equipment cabinets.

In the era of the glass room, mere mortals were never permitted into the computer room. Their access was limited to a small job submission window where they could hand the technicians a magnetic tape reel or a deck of punched cards.

Here's a classic "glass room" from the late 1970's. This one was at the Central Administrative offices for the State University of New York. The square floor tiles are a "raised floor" to cover the cabling and cooling lines needed to operate the mainframes of that era.

In this interior view, the two foreground rows are disk drives, with tape drives in the background. A typical modern desktop computer has greater storage and processing capacity than all of the equipment in this room from 30 years earlier.

(These photos are courtesy of Kenneth Hapeman)