Game Like it is 1983

The first computer I ever physically saw — I think — was an IBM System/3. You might not remember them. They were business computers for businesses that couldn’t justify a big mainframe. They were “midrange.” Nevermind that the thing probably had the memory and processing speed of the CPU inside my mouse. Time progressed and IBM moved on to the System/3x (for example, the System/32). Next up was the AS/400 and finally the IBM i, which is still in production. Here’s a secret, though, most of the code I’ve seen running on an IBM i dates back to at least the System/3 days and maybe even before that.

If you are interested in history, or midrange computers (which are mainframe-like in their operation), you might want to actually play with a real machine. A quick glance at eBay tells me that you might be able to get something workable for about $1000. Maybe. That’s a bit much. What if you could get time on one for free? Turns out, you can.

The Cloud Option

Head over to and register for an account. This won’t be instant — mine took a day or two. The system is for educational purposes, so be nice and don’t use it for commercial purposes. You get 150MB of storage (actually, some of the documentation says 250MB, and I have not tested it). While you are waiting for your account, you’ll need to grab a 5250 terminal emulator and adjust your thinking, unless you are a dyed-in-the-wool IBM guy.

Even though the IBM i looks like an old 1970’s midrange, the hardware is quite modern with a 64-bit CPU (and the architecture can handle 128 bits) and well-known stability. However, the interface is, well, nostalgic.


Depending on your host computer, there are several IBM 5250 terminal programs available. They recommend tn5250 or tn5250j which use Java. However, I installed Mochasoft’s emulator into my Chrome browser. It is a 30-day free trial, but I figure in 30 days I’ll be over it, anyway.

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The PDP-1: The Machine that Started Hacker Culture

One of my bucket list destinations is the Computer History Museum in Mountain View, California — I know, I aim high. I’d be chagrined to realize that my life has spanned a fair fraction of the Information Age, but I think I’d get a kick out of seeing the old machines, some of which I’ve actually laid hands on. But the machines I’d most like to see are the ones that predate me, and the ones that contributed to the birth of the hacker culture in which I and a lot of Hackaday regulars came of age.

If you were to trace hacker culture back to its beginning, chances are pretty good that the machine you’d find at the root of it all is the Digital Equipment Corporation’s PDP-1. That’s a tall claim for a machine that was introduced in 1959 and only sold 53 units, compared to contemporary offerings from IBM that sold tens of thousands of units. And it’s true that the leading edge of the explosion of digital computing in the late 50s and early 60s was mainly occupied by “big iron” machines, and that mainframes did a lot to establish the foundations for all the advances that were to come.

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A 2,200 Pound Personal Computer

[Connor Krukosky] wanted to buy another computer. Even though he is only 18, he had his first computer at 18 months old. He’s had plenty since then and his interest in computers led him to pursue a career in electrical engineering. A few years ago, [Conner] started collecting vintage computers.

He’d bought up some Apple computers, terminals, and even a Data General minicomputer. Then he found a notice that Rutgers was auctioning off an IBM z890 mainframe computer. People warned [Conner] that this wasn’t a desktop workstation, it was a 2,200 pound case that probably wouldn’t fit through standard doors.

He was undeterred. He won the auction for under $240. The real expense, of course, would be moving it. He planned to make two trips: One to strip the machine to parts and bring some parts back and then a second trip to get the remaining parts.

You can see in the video below that he had a lot of adventure moving the beast. Things didn’t fit and even some excavation had to happen to get the computer in his basement.

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The IBM 1401’s Unique Qui-Binary Arithmetic

Old mainframe computers are interesting, especially to those of us who weren’t around to see them in action. We sit with old-timers and listen to their stories of the good ol’ days. They tell us about loading paper tape or giving instructions one at a time with toggle switches and LED output indicators. We hang on every word because its interesting to know how we got to this point in the tech-timeline and we appreciate the patience and insanity it must have taken to soldier on through the “good ol’ days”.

[Ken Shirriff] is making those good ol’ days come alive with a series of articles relating to his work with hardware at the Computer History Museum. His latest installment is an article describing the strange implementation of the IBM 1401’s qui-binary arithmetic. Full disclosure: It has not been confirmed that [Ken] is an “old-timer” however his article doesn’t help the argument that he isn’t.

Ken describes in thorough detail how the IBM 1401 — which was first introduced in 1959 — takes a decimal number as an input and operates on it one BCD digit at a time. Before performing the instruction the BCD number is converted to qui-binary. Qui-binary is represented by 7 bits, 5 qui bits and 2 binary bits: 0000000. The qui portion represents the largest even number contained in the BCD value and the binary portion represents a 1 if the BCD value is odd or a 0 for even. For example if the BCD number is 9 then the Q8 bit and the B1 bit are set resulting in: 1000010.

The qui-binary representation makes for easy error checking since only one qui bit should be set and only one binary bit should be set. [Ken] goes on to explain more complex arithmetic and circuitry within the IBM 1401 in his post.

If you aren’t familiar with [Ken], we covered his reverse engineering of the Sinclair Scientific Calculator, his explanation of the TL431, and of course the core memory repair that is part of his Computer History Museum work.

Thanks for the tip [bobomb].

The Most Powerful Bitcoin Mining Rig Yet

In days of yore, one could mine Bitcoin without much more than an AMD graphics card. Now, without specialized hardware it’s unlikely that you’ll make any appreciable headway in the bitcoin world. This latest project, however, goes completely in the other direction: [Ken] programmed a 55-year-old IBM mainframe to mine Bitcoin. Note that this is technically the most powerful rig ever made… if you consider the power usage per hash.

Engineering wordplay aside, the project is really quite fascinating. [Ken] goes into great detail about how Bitcoin mining actually works, how to program an assembly program for an IBM 1401 via punch cards, and even a section about networking a computer from this era. (Bonus points if he can get to load!) The IBM boasts some impressive stats for the era as well: It can store up to 16,000 characters in memory and uses binary-coded decimal. All great things if you are running financial software in the early ’60s or demonstrating Bitcoin in the mid-2010s!

If it wasn’t immediately obvious, this rig will probably never mine a block. At 80 seconds per hash, it would take longer than the lifetime of the universe to do, but it is quite a feat of computer science to demonstrate that it is technically possible. This isn’t the first time we’ve seen one of [Ken]’s mainframe projects, and hopefully there are more gems to come!

Generating the Mandelbrot Set With IBM Mainframes

[Ken Shirriff] is apparently very cool, and when he found out the Computer History Museum had a working IBM 1401 mainframe, he decided to write a program. Not just any program, mind you; one that would generate a Mandelbrot fractal on a line printer.

The IBM 1401 is an odd beast. Even though it’s a fully transistorized computer, these transistors are germanium. These transistors are stuffed onto tiny cards with resistors, caps, and diodes, than then stuck in a pull-out card cage that, in IBM parlance, is called a ‘gate’. The computer used decimal arithmetic, and things like ‘bytes’ wouldn’t be standard for 20 years after this computer was designed – 4,000 characters of memory are stored in a 6-bit binary coded decimal format.

To the modern eye, the 1401 appears to be a very odd machine, but thanks to the ROPE compiler, [Ken] was able to develop his code and run it before committing it to punched cards. An IBM 029 keypunch was used to send the code from a PC to cards with the help of some USB-controlled relays.

With the deck of cards properly sorted, the 1401 was powered up, the cards loaded, and the impressive ‘Load’ button pressed. After 12 minutes of a line printer hammering out characters one at a time, a Mandelbrot fractal appears from a line printer. Interestingly, the first image of the Mandelbrot set was printed off a line printer in 1978. The IBM 1401 was introduced nearly 20 years before that.

NYC Resistor gets a PDP-11/34

PDP-11/34 NYCR

[Trammel Hudson] and NYC Resistor have gotten their hands on some old computing iron in the form of a PDP-11/34.  The PDP-11 is a 16 bit minicomputer made by Digital Equipment Corporation (DEC). Various incarnations of the PDP-11 were sold from the 1970’s all the way into the 1990’s. NYC Resistor’s model is has a label dating it to 1983.

The PDP was found in an old storage unit in the Bronx. Moving several racks of equipment across the city is no small feat, but NYC Resistor members have it done it so many times they’ve got it down to a science.

Once power is applied, a stock PDP won’t actually do anything until the boot loader is keyed in from the CPU front panel. Thankfully this particular PDP-11 had its boot instructions printed on a label on the CPU. NYCR’s machine also includes an M9312 “bootstrap / Unibus terminator” board, which allows the machine to boot at the push of a button.

The team connected the racks, terminals, and drives. Carefully following the instructions, they actually got their PDP to boot up! Their next step is to start reading in some of the old tapes that came with the machine. We’re all waiting with bated breath to see what “digitized monkey brains” contains. Once the machine is fully functional, we hope they get it on the internet and load up The Hackaday Retro Edition.

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