# A PDP-8 Emulator Revisited on the iPad

DevFeed: [A PDP-8 Emulator Revisited on the iPad](<https://devfeed.tech/articles/roots-21796.md>)

Original publisher: [Read original article](<http://blog.cleancoder.com/uncle-bob/2021/09/25/roots.html>)

Published: 2021-09-25T00:00:00Z

Content type: opinion

Language: en

Sources: [Robert C. Martin](<https://devfeed.tech/sources/robert-c-martin.md>), [The Clean Code Blog](<https://devfeed.tech/sources/the-clean-code-blog.md>)

Topics: [Emulator](<https://devfeed.tech/topics/emulator.md>), [Lua](<https://devfeed.tech/topics/lua.md>), [Code](<https://devfeed.tech/topics/code.md>), [GitHub](<https://devfeed.tech/topics/github.md>), [App](<https://devfeed.tech/topics/app.md>)

Tags: [app](<https://devfeed.tech/tags/app.md>), [code](<https://devfeed.tech/tags/code.md>), [emulator](<https://devfeed.tech/tags/emulator.md>), [github](<https://devfeed.tech/tags/github.md>), [lua](<https://devfeed.tech/tags/lua.md>)

## AI overview

The author recounts building a PDP-8 emulator in Codea on an iPad, losing access to it after Apple restricted source-code sharing, and later restoring and updating it from GitHub.

## Source excerpt

When I was 15 or so, my father would drive me, and my best friend, Tim Conrad, to the Digital Equipment Corporation (DEC) sales office each Saturday. This was a 30 min drive. My father would drop us off in the morning and pick us up in the late afternoon. He spend two hours in his car each Saturday hauling us around. Thanks Dad! Tim and I would spend our day "playing" with the floor model of the PDP-8 they had at the office. The office staff were very accommodating and accepting of our presence, and they helped us out if we needed any fresh rolls of teleprinter paper, or paper tape. Several years later, at the age of 20, I found myself working at Teradyne Applied Systems in Chicago. The computer we used there was called an M365; but it was really just an upgraded PDP-8. We used it to control lasers in order to trim electronic components to very precise values. Forty four years later, in May of 2015, I started playing with a cute little Lua environment on my iPad called Codea. I wrote several fun little programs, like lunar lander, etc. But then I thought: "Wouldn't it be fun to write a PDP-8 Emulator?" A few days/weeks later I had a nice little PDP-8 emulator running on my iPad. I found some archived binary images of ancient paper tapes and managed to load them into my emulator. This allowed me to run the suite of development tools that I had used back in those early days. Then Apple decided it didn't want people writing code on the Ipad that was not distributed through the App store, so they blocked the means by which Codea users could share source code. Indeed, I couldn't even move Lua source code to my new iPads. So the emulator was lost. Fortunately I had put the last working version up on GitHub. At some point, Apple reopened the channel, perhaps due to a court case. I discovered this a few weeks back, and loaded that old source code back into my iPad. It worked like a champ. I made a few changes to deal with the bigger screen, and the faster processor, and the