Hershey Fonts: Not Chocolate, The Origin Of Vector Lettering

Over the past few years, I kept bumping into something called Hershey fonts. After digging around, I found a 1967 government report by a fellow named Dr. Allen Vincent Hershey. Back in the 1960s, he worked as a physicist for the Naval Weapons Laboratory in Dahlgren, Virginia, studying the interaction between ship hulls and water. His research was aided by the Naval Ordnance Research Calculator (NORC), which was built by IBM and was one of the fastest computers in the world when it was first installed in 1954.

The NORC’s I/O facilities, such as punched cards, magnetic tape, and line printers, were typical of the era. But the NORC also had an ultra-high-speed optical printer. This device had originally been developed by the telecommunications firm Stromberg-Carlson for the Social Security Administration in order to quickly print massive amounts of data directly upon microfilm.

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Extracting A Vector Font From A Vintage Plotter

There is a huge variety of hardware out there with a font of some form or other baked into the ROM. If it’s got a display it needs a font, and invariably that font is stored as a raster. Finding these fonts is trivial – dump the ROM, render it as a bitmap, and voilĂ  – there’s your font. However, what if you’re trying to dump the font from a vintage Apple 410 Color Plotter? It’s stored in a vector format, and your job just got a whole lot harder.

The problem with a vector font is that the letters aren’t stored as individual images, but as a series of instructions that, when parsed correctly, draw the character. This has many benefits for generating characters in all manner of different sizes, but makes the font itself much harder to find in a ROM dump. You’re looking for both the instructions that generate the characters, as well as the code used to draw them, if you want a full representation of the font.

The project begins by looking at what’s known about the plotter. The first part of any such job is always knowing where to look, of course. It’s quickly determined that the font is definitely stored in the main ROM, and that there is no other special vector drawing chip or ROMs on board. The article then steps through the search process, beginning with plaintext searches of the binary dump, before progressing to a full disassembly of the plotter firmware. After testing out various assumptions and working methodically, the vector data is found and eventually converted into a modern TrueType font.

In the end, the project is successful, and it’s a great guide on how to approach similar projects. The key is to lay out everything you know at the start, and use that to guide your search step by step, testing and discarding assumptions until you hit paydirt. We’ve seen similar works before, like this project to dump the voice from an ancient Chrysler Electronic Voice Alert.