Welcome to decuser's blog
Topics on this blog include computing, retro-computing, operating systems, math, and whatever other technical subjects I happen to be exploring that I find interesting enough to take and share notes about.
Posts
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pdp-11 analysis
Analysis of the PDP-11 bootstrap loader code
This note describes, in detail, how the bootstrap loader code operates. While it is only 14 words, it is not trivial to understand. The bootstrap loader is self-modifying code
The note is a work in progress. It begins by describing the first iteration where the loader loads a single byte from the tape reader. In this case the byte is octal 351, which is the first byte of the absolute loader and is the tape leader byte. Octal 351, when read by the bootstrap loader has the effect of causing the boot strap loader to overwrite a portion of itself that results in no change to its memory contents. Any other value, when read will cause the bootstrap loader to begin copying bytes into a memory location prior to the bootstrap loader itself and continuing to copy bytes until the bootstrap loader overwrites itself with the contents of the loaded program. Programs that are bootstrap loader programs contain a footer that restores they original bytes of the bootstrap loader except for the starting location.
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unix research-unix v6
Adding tar to Research Unix Version 6 Running on a PDP 11/40 in SimH
This note explains an approach to getting a working version of tar running on Research Unix Version 6 (v6) running in a SimH PDP-11/40 Simulator.
NOTE: After working at this for a bit, it is clear to me that while this is workable as a solution to move files from v6 to v7, it is not workable as a true tar for v6. The program has difficulty with directories, timestamps and such when working natively on v6. The issues are not with the instructions outlined below, but rather with limitations of the original program as delivered with v7. More investigation is required to understand its limitations.
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unix research-unix v7
Installing and Using Research Unix Version 7 in SimH PDP-11/45 Emulator
This note is intended to document the process of running v7 in a PDP-11/45 emulated environment. A previous note covers [v6]({% post_url 2015-11-23-installing-and-using-research-unix-v6-in-simh-pdp-11-40-emulator %}) originally posted November 23, 2015 and there is a more recent note covering [v7]({% post_url 2017-10-11-installing-and-using-research-unix-v7-in-simh-pdp-11-45-and-70-emulators-rev-1.6 %}).
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unix research-unix v6
Installing and Using Research Unix Version 6 in SimH PDP-11/40 Emulator
This note is intended to document the process of running v6 in a PDP-11/40 emulated environment. A subsequent note covers [v7]({% post_url 2015-12-07-installing-and-using-research-unix-v7-in-simh-pdp-11-45-and-70-emulators-rev-1.0 %})
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hardware raspberry-pi
Raspberry Pi B+, i2c, and DS3231 RTC
Here are some notes on how to get your pi talking to a cheapo DS3231 Realtime clock using nothing more than a pi, an ethernet cable (for downloads), a serial cable, and an RTC.
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programming mono
HelloMono - Mono on Windows XP
An article I wrote back in the day (2004-05-06)and published on CodeProject. The article is rated 4.11 and has been viewed more than 229k times as of October 21, 2025.
https://www.codeproject.com/articles/HelloMono-Mono-on-Windows-XP
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programming c#
hello, world - A primitive view of the state of the art
An article I wrote back in the day (2004-04-30) and published on CodeProject. The article is rated 4.67 and has been viewed more than 161k times as of October 21, 2025.
https://www.codeproject.com/articles/hello-world-A-primitive-view-of-the-state-of-the-a
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programming c++
LogDriver - A simplified log4j using C++
An article I wrote back in the day (2002-01-04) and published on CodeProject. The article is rated 4.73 and has been viewed more than 192k times as of October 21, 2025.
https://www.codeproject.com/articles/LogDriver-A-simplified-log4j-using-C-