The Iowa Stater
Dec. 15, 1995
Rebuilding 1930s computer
not as easy as A-B-C
Gary Sleege and John Erickson have collected nearly 500 vacuum tubes and ordered yards of cotton-rubber insulated wire, both relics of a time past. Now, if they can get their hands on an IBM punch, Christmas will come early for them.
Sleege, Erickson and six other engineers are part of a team that is building a full-scale replica of the Atanasoff-Berry Computer (ABC). The ABC, the world's first electronic digital computer, was built on campus by professor John Atanasoff and his graduate student Clifford Berry in the late 1930s and early 1940s.
The reconstruction, a tribute to the computer pioneers, requires the usual engineering skills, but also a considerable talent for scavenging. The IBM punch, which perforated cards used for data entry in the pre- laptop days of computers, is an example.
"There were many thousands of these punches all across America," said Del Bluhm, manager of research and development engineering at Ames Lab and director of the replica project. "They've all disappeared."
"It's like trying to find an authentic spinning wheel," added John Gustafson, an Ames Lab computational scientist and replica team member.
The ABC replica project is not your Heath-kit variety nostalgia trip. The parts don't come easy - and they don't come with detailed diagrams. The original drawings and design notes were discarded in the 1940s as well as the ABC itself.
"We thought it would be easier to build [the ABC] in 1995 than it was in 1939," Bluhm said. "But we are reengineering and recreating what they did in the 1930s, so all of the hours they spent in design and building, we will probably respend."
"Access to parts and subtle differences in the how things are done get in the way all of the time," added Gustafson. "We can't use technology to shortcut a few things. It wouldn't be authentic."
Which is why the team agonizes over the use of plastic-insulated wires of today or the cotton-rubber insulated wires of yesteryear. The team has assembled a varied collection of 1940s electronic paraphernalia from their visits with antique radio buffs (to acquire vacuum tubes), neon sign manufacturers (transformers), gear companies (gears and bearings) and specialty plastics manufacturers (a special material for the drums). Sometimes, they're lucky enough to have copies of Atanasoff's original purchase orders to guide them. More often, they have only a grainy photograph and some fading memories.
"It's sort of like Sherlock Holmes' detective work - a piece of information here, a piece of information there, add a picture and come to conclusions as to what that component did," said Sleege.
"We guess a lot," Erickson added.
Without documentation, just determining the ABC's dimensions was a chore. The team determined the height of the machine from a photograph of it in front of a door. "Door knobs are all the same height," team member Dave Birlingmair said. "From that, we could figure the height of the machine."General dimensions of the replica are 32-inches wide, 6- feet long and 34-inches high.
Help from friends
An invaluable resource for the team has been contact with those either
directly or indirectly involved in the original project. In the fall of
1994, Erickson and Birlingmair paid a visit to the Atansoff family.
Armed with a portable copy machine, they spent two days visiting with
the family and copying original documents and purchase orders.
Another big help has been Robert Mather, a retired physicist in Oakland, Calif. A graduate student in the late 1930s and early 1940s, Mather wired the original ABC under the direction of Berry.
"He still has a pretty good memory of how things were laid out," Gustafson said. This will be helpful for Sleege, who is in charge of replica electronics, because documentation of ABC electronics is spotty at best.
Mather helped the team figure out where ABC's output was read, a mystery the team faced early in the project. Scientists read the computed answer by peering into an axle to find odometer numbers rotating into place.
"[Mather] showed us where the output was created," Bluhm said. "We went back and looked at enlarged pictures of the ABC and said 'By golly, he's right!'"
Paper and fire
A formidable problem the team currently is
grappling with is the electronic read and write system of the ABC. The
system acted as sort of scratch paper for the computer as it worked its
way through an equation.
"Atansoff had to devise a way to record 1,500 bits of data per second and there was no method in the world for doing that at the time," Birlingmair said. "IBM punches could handle 10, 20 or 30 numbers per second. So he devised a system in which ABC burned holes in paper with a spark. These were called electrostatic punches. Later, the computer would find out where these holes were and read the data."
"It's incredible that it worked," Gustafson said. "And they got it so that it failed only once every 10,000 to 100,000 times."
The ABC had 30 such electrostatic punches working in unison. So far, Erickson has been successful zapping holes in paper, but only on one punch. Getting 30 to work in unison will be trickier.
Zapping the paper without igniting it is tricky as well. The wrong paper, Bluhm said, "will catch on fire." Atanasoff and Berry eventually found a type of paper that worked, but never documented it.
After struggling to fine paper, the team finally turned to Jean Berry (Clifford Berry's wife and Atanasoff's secretary). "She knew the name of the paper and where we could buy it right off the top of her head," Gustafson said.
The smell of computing
When the ABC is completed (scheduled for August 1996), the team will
operate the replica at least once, hoping to match the performance of
the original. While designed to solve 29 simultaneous equations with 29
unknowns, an operation that would take nearly 50 hours of ABC computing
time alone, it's believed that the original only solved five equations
with five unknowns.
"If we can solve five equations and five unknowns and get the right
answer, I'll be satisfied that we succeeded," Gustafson said. "The rest
is cosmetic."Cosmetics should be the easy part. "We need to know what
color the lights were," Gustafson added. "We only have black and white
photographs to go on. What did it sound like? I have a feeling that it
probably produced an odor because of those sparks punching holes in the
paper. It must have smelled like a thunderstorm just happened."
- Skip Derra, News Service
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