The GE-115 Project

 All of the changes (ie. correction of mistakes) identified in the GE-115 System Manual have been made.  The biggest challenge was to switch the conditional jumps, which use a mask of complementary conditions, to a mapping from two status bits, zero and overflow. There is a nice way to do this by mapping the four status combinations from two bits into 4 different mask values. I retested my test programs, and had to make a few changes, sometimes to the test program (due to an improved understanding of what was supposed to happen) and sometimes to correct errors in the simulator which came to light. All in all, the transition was pretty smooth. So the new simulator, assembler and Fortran compiler are ready to go out to be tested in a larger context. I have started work on a website which will allow people to request instructions for downloading the simulator. I am thinking an FTP transfer might be the most efficient way to distribute for now.  With the website, I am thinkin...

What an exciting development! On Friday, I was able to download the GE-115 System Manual which had been digitized at the Computer History Museum in Mountain View, California. What an amazing document!!! There is a link at the end of this post so that you can read it yourself. First, I want to express my thanks to Penny and her colleagues at CHM. They are doing great work preserving important aspects of computer history. Without them, this manual and many others would have ended up in a landfill instead of a knowledge-fill. Kudos to everyone! Here is a link to their site: Computer History Museum My experience of reading this manual was first a sense of deja vu. I had first read this manual, published in 1966, in about 1970. I had poured over it, trying to take in all the detail as I tried to learn how to tame the beast and bend it to my will. (A little overly dramatic there, sorry about that, but that's what it felt like). The nuances of why things worked one way and not another. I ...

Progress slowed a little bit in July, as my vacation is over and I am back to teaching. It did take another month for testing and finishing touches on the Fortran compiler. It now does everything that the GE-115 Fortran did and a few bonus things as well. It was tempting to add new features, but I have tried to remain true to recreating the past and not improving on my recollections too much! As an example, the GE-115 did not have logical variables, as I recall, so the compiler does not support this. However, all the infrastructure is there to turn that feature on. There is always something more to do. I have not implemented the entire library of run time routines that were part of the Fortran library. These are pretty easy to knock off and I will tackle them at leisure. For example, there is a SIN function to calculate the sin of an angle. To implement it, I don't need to write something in assembler to implement an algorithm to calculate the correct result. Instead, I just need...