Falk Rehwagen, TopDesk and GEOS

Here are some of Falk Rehwagen’s thoughts on his involvement with GEOS and TopDesk.

It’s not so easy to remember the details after more than 25 years πŸ™‚


Back then, I was fascinated by what one could get out of this outdated hardware, many years after its release. As for GEOS, I found it exciting that it was possible to develop a real commercial operating system on such a small machine, with a variety of powerful applications, tools, drivers, and so on. Naturally, I bought GEOS as soon as it was possible, paid with my family’s welcome money in Berlin, 1990. πŸ™‚

Programming & GEOS User Club

That’s when I got very involved with GEOS (64) and its possibilities on my C128, and it quickly became clear that I wanted to develop applications myself. I a found good and fast entry with the MegaAssembler, which paved the way deep into GEOS development. As part of this learning, I created a diverse set of applications, which, compiled as a “best of” disk, we also offered for sale. In this context, in 1991/92, I got into contact with the Geos User Club, the association of all GEOS users and fans in Germany. The “GUC-Regio-Sachsen” was founded, and in 1992, I participated in the GUC Annual General Meeting for the first time. If I remember correctly, this was also the time when TopDesk was almost ready as a the modern replacement for the “deskTop” built into GEOS. It was absolutely fascinating, because the windowing technology once again showed what can be done with GEOS and the hardware and brought the system closer to the more modern competitors. TopDesk was delayed, but eventually I held it in my hands and used it as my exclusively GEOS control center.

Patch System and GeoCOM

I was keen to make GEOS better and more flexible. From this thought arose the “Patch System”, which allowed defining and distributing small improvements and extensions in a consisteny way. In order to give more users and developers the opportunity to develop new applications for GEOS, a powerful programming environment called GeoCom was created, based on ECOM from the 64’er Magazine. With an extensive manual, created in co-operation with Denis DΓΆhler, the system was offered commercially as a alternative to programming in assemnly.

TopDesk Maintainer

Around the same time, the market around PCs and operating systems developed rapidly, many GEOS fans following the technological development towards PC/GEOS or other available alternatives. I think sometime in 1993/94, the GUC had completely switched its focus on PC/GEOS and was looking for maintainers for its GEOS-64-related technologies and products. With my spectrum of projects and experience, I was probably a good candidate for this: After all, I remained faithful to the C64/128 and GEOS 64 as a developer. I don’t remember when and where exactly, but I was given TopDesk maintainership – and the sources. πŸ™‚ It was convenient that TopDesk had been written by the same people as MegaAssembler, so I was already well-equipped for the development of TopDesk.

Improving GEOS and TopDesk

After “Patch System” and GeoCom, I wanted to develop GEOS in a more profound way, to combine it with the extended TopDesk, and to make the whole system more open to the many hardware enhancements that were available on the market. For this purpose, I completely reverse-engineered the GEOS KERNAL (with all-GEOS tools like GEODISASSEMBLER), so it could be assembled again with MegaAssembler. The idea for GEOS 3.0 was born. Development became much faster after I had gotten a loaner Flash 8 acceleration cartridge (8 MHz) – for which I adapted GEOS. TopDesk got color support, and the GEOS KERNAL was further developed to have a flexible driver model. An early version of the project was presented in Berlin at the GUC Annual General Meeting 1994.

After GEOS 64

I think I had already decided to take the step towards the PC at that time, to intensively work my way into the PC/GEOS SDK, which had just been published. (However, various sources seem to state that PC/GEOS wasn’t released until April 1995…) At least that’s when I decided to turn my back on GEOS 64 (initially) and to take on new challenges as part of my university studies. For this reason, the current state of development of TopDesk and GEOS 3.0 was cleanly returned to the GUC – to Wolfgang Grimm, I think. This soon resulted in version 3.0 of TopDesk, which was developed further as part of the MegaPatch 3.

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