mjgraf.net

Bringing an old computer back to life

Sat, 31 Jan 2026 00:00:00 +0000

Slowly returning to the retrocomputing hobby after 12 14 many years, most of my collection has been in storage way longer than I anticipated in 2006.¹

That means I’ll have to treat every machine I take out of storage essentially as an unknown. That’s why I looked around on the internet for some best-practice checklist on how to proceed with “new” old computer, but couldn’t find anything.²

So here’s my attempt. I’ll extend and modify it as I take more and more machines out of storage. I welcome your feedback.

A Pseudo-Random List of Retrocomputing Reverse Engineering Links

Fri, 23 Jan 2026 00:00:00 +0000

Another list I’m putting together for my own benefit (the first one is here).

Reverse Engineering Frameworks

Ghidra

Ghidra is a free, open-source software reverse engineering (SRE) suite developed by the U.S. National Security Agency. It’s primarily used to analyze compiled binaries, allowing users to disassemble, decompile, and inspect low-level code. One of its standout features is a powerful decompiler that attempts to reconstruct readable high-level code from machine instructions. Ghidra supports many processor architectures and file formats, making it useful for malware analysis, vulnerability research, and firmware inspection. It also includes scripting and collaboration features.

Liniertes und gepunktetes Papier zum Selberausdrucken

Thu, 01 Jan 2026 00:00:00 +0000

Nochmal auf Deutsch, damit das Thema auch von denen gefunden wird, die auf Deutsch danach suchen.

Ich schreibe gerne mit der Hand, am liebsten mit Füller auf liniertem Papier. Und weil mir Kleinigkeiten manchmal wichtig sind: am allerliebsten auf liniertem Papier mit 8mm Zeilenabstand, statt der in deutschen Schulheften üblichen 9mm.

Nun werden linierte Blöcke in Büromaterialschränken immer selterner; Laserdrucker dagegen stehen überall. Deshalb habe ich mir Druckvorlagen für liniertes, gepunktetes (statt: kariertes)¹, und vorne liniertes, hinten gepunktetes doppelseitiges A4-Papier erstellt, außerdem gepunktetes einseitiges A3 Papier für größere Zeichnungen.

Print Your Own Ruled or Dotted Paper

Thu, 01 Jan 2026 00:00:00 +0000

I love writing by hand, preferably with a fountain pen, even though my handwriting is terrible. Unfortunately, decent notepads and notebooks seem to disappear from many office supply cupboards, so I decided to make my own notepaper templates to print wherever and whenever I need some.

Take your pick of ruled, dotted, or front-ruled-back-dotted hybrid double-sided A4 paper, or dotted single-sided A3 paper for those large drawings.

Share and Enjoy,¹ but don’t forget to attribute when you share!

Extracting all images from an Evernote Export (.enex) file

Fri, 01 Jan 2021 00:00:00 +0000

While it’s quite easy to get a large number of images into an Evernote note, it’s hard work to get them all out again: you have to right-click them one by one, then “Save as…” each one.

However, Evernote does let you export the entire note ‒ and even several notes at once ‒ into one .enex file. .enex files are XML, with each image base64 encoded and neatly enclosed in a <resource> tag. So here is a perl script that will take a list of .enex files as command line arguments, and write all the images from each of them to the current folder.

Classic Computer Collector's Code of Conduct

Sun, 05 Jan 2020 00:00:00 +0000

I have no idea where this originally came from, but it’s been around for some 20 years (at least), and I rather like it. Copied from Gaby’s CP/M site.

As a serious collector, I follow the Classic Computer Collector’s Code of Conduct (CCCCC). The CCCCC is listed here for your reference:

I will do my best to find a home for any classic or unwanted computer.
I will return or destroy any personal or commercially sensitive data I find on a machine I acquire, and will keep it in the strictest confidence, should I find it necessary to view it.
I will aid users in the decomissioning of their machines, should they require assistance.
I will respect active software and publication copyrights.
I will, whenever possible, repair the computers in my collection and maintain them in working order, and will assist others in doing the same, to the best of my ability. I will actively encourage the repair, maintenance, and use of older computers, in preference to the irreversable alteration of machines and parts for non-computer applications.
I will actively promote the exchange of computers, parts, and information among collectors, and will refrain from hoarding multiple examples of any item.
I will actively promote ethical collecting.

Repairing an AVR DDS Signal Generator

Sat, 11 Aug 2018 00:00:00 +0000

Background

As far as I can tell, the first use of an AVR to do direct digital synthesis of an analog signal was by Jesper Hansen in 2001. Mindaugas Marozas picked up the idea to create a stand-alone function generator in 2006. In 2008, Mindaugas published an improved version, which has become the basis of many homebrew projects, as well as a number of Chinese clones. Georg Latzel, DL6GL, gives a very nice and detailed rundown of the theory of operation (in German).

What I learnt today...

Mon, 23 Jul 2018 00:00:00 +0000

… is that on the AVR, the “Data Memory Usage” information given by AVRGCC only refers to memory allocated at compile time, and does not take the stack into account.¹² The stack is not to be underestimated: it holds not only the return addresses from function calls, but also all local variables³ of the function(s) called.

So you might feel safe and sound reading something like “Data Memory Usage : 66 bytes 51,6% Full”, thinking there’s plenty of space left for future features; and then the stack still swoops down and corrupts your precious data because of a couple of nested function calls.

Inside the Kosmos CP1

Mon, 18 Jun 2018 00:00:00 +0000

Originally, I planned to save all the CP1 stuff for a later post, but there’s this one picture I really want to share. After removing the cardboard back cover,

this is what I saw:

The screwdriver must have been in there for some 15 years at least.

A Pseudo-Random List of Retrocomputing Links

Mon, 01 Jan 0001 00:00:00 +0000

I’ve put this list together as much for my own benefit as for that of potential readers. The only selection criterion was “stuff that I find intersting and want to be able to go back to later.”

Yes, I know browser bookmarks exist.

Blogs & Podcasts

Ken Shirriff’s blog: Xerox Alto restoration, IC reverse engineering – http://www.righto.com

Programming Languages

The Retrocomputing Museum – Languages From Hell — Co-curated and hosted by ESR. Don’t veer into the political parts of his site, it might spoil the fun… ;-)

General / Platform independent

old-computers.com
8bit-homecomputermuseum.at
8-Bit-Nirvana
CPU Shack
AntiqueTech also has a directory of old CPUs
Bitsavers
Datormuseum
Bytecollector – while no longer actively collecting, Bryan covers the very early years of the microcomputer revolution on his site.
The Museum of Obsolete Media
Erik S. Klein’s The Vintage Computer
oldcomputers.net (nice timeline!)
The Internet Archive is more than just the Wayback Machine: Amongst many other things, they also have books and magazines about and software for old computers and consoles, and lots of it. However, unlessyou know what you are looking for, the archive is a bit hard to navigate.

Homebrew

Lee Hart’s Altoid-tin-sized single board computers, the COSMAC ELF Membership Card and the Z80 Membership Card. Lee is also working on putting an Altarir 8800 into an Altoids tin, using only components available at the time.
Grant Searle has built replicas of the Sinclair ZX80, the Jupiter ACE, and the CompuKit MicroUK101, as well as a 6809 and a CP/M machine of his own design.
As his website was unavailable recently, here’s an archived copy at the internet archive.

Counterfeit ICs

A major source for obsolete ICs to use in retro-homebrew projects are Chinese sellers on eBay. Unfortunately, many of them don’t seem to care whether the ICs they sell are genuine or counterfeit. Here are a couple of pages about spotting counterfeit ICs

Datenschutzerklärung

Mon, 01 Jan 0001 00:00:00 +0000

Präambel

Mit der folgenden Datenschutzerklärung möchte ich Sie darüber aufklären, welche Arten Ihrer personenbezogenen Daten (nachfolgend auch kurz als “Daten” bezeichnet) ich zu welchen Zwecken und in welchem Umfang verarbeite. Die Datenschutzerklärung gilt für alle von mir durchgeführten Verarbeitungen personenbezogener Daten, sowohl im Rahmen der Erbringung meiner Leistungen als auch insbesondere auf meinen Webseiten, in mobilen Applikationen sowie innerhalb externer Onlinepräsenzen, wie z.B. meiner Social-Media-Profile (nachfolgend zusammenfassend bezeichnet als “Onlineangebot”).

Impressum

Mon, 01 Jan 0001 00:00:00 +0000

Angaben gemäß § 5 DDG:

Michael Graf
Mühlwinkel 12
84419 Obertaufkirchen

Kontakt:
Telefon: 08082-2713060
Fax: 08082-9483713
E-Mail: web@mjgraf.net

Verantwortlich für den Inhalt nach § 18 Abs. 2 MStV:
Michael Graf, Anschrift und Kontakt wie oben

Haftungsausschluss:

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Die Inhalte dieser Seiten wurden mit größter Sorgfalt erstellt. Für die Richtigkeit, Vollständigkeit und Aktualität der Inhalte kann ich jedoch keine Gewähr übernehmen.

Haftung für Links

Diese Website enthält Links zu externen Webseiten Dritter, auf deren Inhalte ich keinen Einfluss habe. Deshalb kann ich für diese fremden Inhalte auch keine Gewähr übernehmen. Für die Inhalte der verlinkten Seiten ist stets der jeweilige Anbieter oder Betreiber der Seiten verantwortlich. Die verlinkten Seiten wurden zum Zeitpunkt der Verlinkung auf mögliche Rechtsverstöße überprüft. Rechtswidrige Inhalte waren zum Zeitpunkt der Verlinkung nicht erkennbar. Eine permanente inhaltliche Kontrolle der verlinkten Seiten ist jedoch ohne konkrete Anhaltspunkte einer Rechtsverletzung nicht zumutbar. Bei Bekanntwerden von Rechtsverletzungen werden wir derartige Links umgehend entfernen.