Theresa Welsh recalls her daughter Amy’s reaction when she and her husband told their grade school age child that computers once filled whole rooms.

Slideshow: Highlights from the 2007 Vintage Computer Festival

“She told me later, ‘What I pictured was this giant keyboard with a giant monitor and somebody jumping on the keys, because I couldn’t think of how else a computer could fill up a whole room,’” Welsh recalled.

Room-sized computers were among the recollections shared at a two-day Vintage Computer Festival in Silicon Valley Nov. 3-4. Up for discussion was how products viewed as primitive today -- a desktop computer with just 4KB of memory; a refrigerator-sized magnetic disk drive with just 5MB capacity; an Intel processor capable of running only a calculator – could have found a market, much less started a revolution. Yet they did.

About 200 people, many of them of the gray-haired pony tail, bifocals and middle-age paunch variety, attended the event at the Computer History Museum in Mountain View, Calif.

Welsh, along with her husband David Welsh, coauthored Priming the Pump: How TRS-80 Enthusiasts Helped Spark the PC Revolution, published in May, a 355-page homage to the first mass-marketed microcomputer in the United States.

Skeptical executives of Tandy Corp. began limited production of 3,500 TRS-80s in 1977, roughly one for each of the company’s 3,400 Radio Shack electronics stores. After one year on the market, Tandy was scrambling to fill 250,000 orders for the $600 computer, David Welsh says.

The TRS-80 had no hard drive, just 4KB of memory, required an attached cassette tape player for storage and became maligned as the “Trash-80” because of its reliability. But before the TRS-80, the next most popular microcomputer was the Altair 8800, which the buyer had to assemble, he says.

Although the TRS-80 was launched the same year as the Apple II and the Commodore PET personal computers (check out other technologies from the 1980s with our slide show), it benefited from the distribution network and brand identity of Radio Shack.

“What the TRS 80 showed was that there was a market that even Radio Shack hadn’t anticipated, and it showed that a device like this could be produced and mass marketed. That opened the floodgates,” he said.