# BIT PLAYERS - Thayer Academy Computer Science

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Bit Players

FOUR THAYER FACULTY MEMBERS CONSTRUCT A BINARYCALCULATOR TO SHOWCASE HOW A COMPUTER REALLY WORKSBy Craig Salters ’86

The bad news: it took four of Thayer’s best and brightest faculty members over 100 hours of work to successfully add 255 to 255.

The good news: they did so to better understand the inner workings of a computer and pass that knowledge on to their students. “This was built, intentionally, as a teaching tool,” said Upper School Math Faculty Tom Chiari P ’22, ’22 as he explained the finer points of the TA-255, the binary calculator he collectively constructed with Upper School Computer Science and Science Faculty Christopher Allen, Kevin Cedrone P ’22, and Don Donovan P ’10, ’13.

The “TA” reference should be obvious; the number “255” refers to the largest input number the device can handle. Put another way: the calculator can add from 0 + 0 up to 255 + 255, so the range of its potential answers is between 0 and (Spoiler Alert) 510.

“All a computer is doing is a lot of very simple calculations very quickly,” said Cedrone, pointing to a row of computers in the Academy’s computer lab which operate to the tune of three to four billion computations per second. “We’re trying to drill down to how a computer actually does what it does.”

The wood-framed TA-255 is roughly the size of a breadbox. It contains eight “switches” for the first inputted number and another eight switches for the second inputted number. There are eight circuit boards, each made up of relays, diodes, and lots of wire, but at the heart of the TA-255 — at the heart of all computers, really — is the binary digit, or “bit” for short. And that simply means 0 or 1.

“Everything a computer does, from adding two numbers to storing your favorite selfie, it does with 0s and 1s,” said Allen. “However, when a computer adds 1 + 1, it doesn’t get 2. Instead, the computer does its work in base 2 and gets 10 as the answer.”

Chiari described the computer’s heart and soulthis way: “You’re basically adding two binarydigits together: 0 + 0, 1 + 0, 0 + 1, or 1 + 1.”Chiari described the project as “a journey”which began when he wanted to better understandhow “binary logic gates” work. Cedronegave Chiari a photocopied chapter of Code:The Hidden Language of Computer Hardwareand Software by Charles Petzold.This book isgiven annually as a computer science prize atCommencement.

“I read the first part of the book once and thesecond part of the book seven times,” saidCedrone.

Long story short: Chiari read the chapter fromthe book, which helped him to fully understandthe logic gate diagram.

Scan the QR code to see a video demonstration of

the TA-255 by Tom Chiari

or visit bit.ly/TA-255

Scan the QR code to watch a video of the TA-255 in action and explained by Tom Chiari

16Thayer Magazine /// Winter / Spring 2019

T H E

I S S U E

OPPOSITE PAGE: Thayer faculty members Chris Allen; Don Donovan P ’10, ’13; Kevin Cedrone P ’22; and Tom Chiari P ’22, ’22 with their creation.

LEFT:The TA-255.

BELOW: Where it all began: the computer book’s logic gate diagram that kicked off the entire enterprise.

It turns out that this diagram is essentially a schematic of how a computer adds two binary numbers together. The author suggested that one could build a simple binary adding machine using wires, relays, diodes, switches, and lightbulbs. The author, however, did not provide any plans for how one would go about this. Nevertheless, Chiari, Cedrone, Allen, and Donovan decided that they would undertake this project.

Both Cedrone and Chiari credited Allen’s knowledge of electrical engineering, with Chiari calling it “invaluable” to the project.

“We would have had zero chance of building this machine were it not for Christopher’s knowledge of all things electrical,” Chiari said.

Donovan laser cut the calculator’s front panel, complete with identifying Thayer insignia. He also laser engraved one side of the calculator with everyone’s name and the date.

“After that, I just cheered them on,” Donovan said.

Also of note: several students attended “wiring parties” where they measured, cut, stripped, and crimped over 150 feet of wire and made the connections to the relays, switches, diodes and LED bulbs of the machine — all without any thought of academic credit.

Chiari and the others are so proud of their creation that they recently entered it into the faculty art show. They see their work as computer

science “from the ground up,” enabling students “to pull out the boards and see the logic of the circuit.”

“If someone knew how to use an abacus, you could do the math much easier and much faster,” explained Allen, “but this calculator is useful because it helps us to understand how computers work.”

So, if you want to understand the roots of computer science, make some calculations on the brand-new TA-255.

But if you’re working with the number 256 or above, you might want to stick with your iPhone.

T H A Y E R

TECH

T I D B I T S

Thayer’s first-ever Computer Club was formed in1979. At right are the first members of the clubfrom the 1980 Black & Orange Yearbook.

Seated (L-R): C. Blaustein, Mr. Church, L. Tonry, A. Abramson; Standing (L-R): N. DePalma, S. Reynolds, C. Walsh, D. Fuller, R. Donovan, C. Kenerson, M. Donovan, R. Shaw, M. Donovan

Thayer Magazine /// Winter / Spring 201917