Fitting 44% More Data on a C64/1541 Floppy Disk
The physical data format on a Commodore 1541 5¼-inch floppy disk as used by the C64 is completely defined in software. The drive’s operating system fits 170 KB on a disk. This article explores different strategies, each with its pros and cons, to fit up to 246 KB.
The Ultimate Game Boy Talk [slides]
The Game Boy is turning 30. To celebrate this, I’m releasing the slides of my “Ultimate Game Boy Talk”, which you may use freely. (Please give credit & point me to derived content.)
Converting the "Competition Pro Extra USB" to C64/Amiga/Atari DB9
- Updated 2025-05-09: Added “SL-6602-TBE” pinout. Thanks a lot to Jörg Knitter!
- Updated 2022-03-09: Added “SL-6603-TWT” pinout. Thanks a lot to Risto K!
- Updated 2022-01-26: Added “V2” pinout.
- Updated 2022-01-22: Added “SL-6603-SPORTS-DE” pinout.
- Updated 2022-01-14: Added “SL-6603-SBK” and “KOKA” pinouts.
- Updated 2022-01-06: Added new “V3” and “V04T” pinouts and instructions on how to use a joystick extension cable.
Speedlink makes several versions of the Competition Pro joystick that have all the physical properties and the excellent switches of the original Competition Pro, but come with a USB interface:
Ultimate Commodore 64 BASIC & KERNAL ROM Disassembly
My side-by-side C64 ROM disassembly/commentary page has been completely redone!
Visualizing Commodore 1541 Disk Contents
G64 files are C64/1541 disk images that contain all bits as they are physically laid out on the 5¼-inch floppy disk. Let’s visualize them!
Building the Commodore TED Kernal with Modern Tools
The original Commodore TED (C16, C116, Plus/4) source code has recently appeared on zimmers.net. It is also available in my Commodore Source Code git repository.
Building the Original Commodore 1541 DOS Source
You might think the DOS ROM of the Commodore 1541 disk drive has been analyzed to death. But here are two new resources:
Book "Anatomy of the 4040 Disk Drive" by Hilaire Gagne
Hilaire Gagne: Anatomy of the 4040 Disk Drive
(HTML, 632K)
Final Cartridge III Monitor for the TED
In my quest to make the C16 more usable, i.e. more like the environment I’m used to, i.e. a C64 with a Final Cartridge III, I’ve ported the Final Cartridge III monitor to the TED series (C16, C116, Plus/4).
C64 Keyboard Layout for the C16
The Commodore 16 is an interesting machine, but the keyboard layout is infuriating. The cursor keys are at an awful place and… and… and… well, it just isn’t the C64 layout I’m used to!
Analyzing the ROMs of Third Party Disk Drives for the C64
Most Commodore 64 users had a 1541 disk drives, but there were always also third part options. Most of them claimed full 1541 compatibility, which sounds impossible without using the same ROM. Let’s analyze the ROMs of some third party drives!
Reconstructing the Unreleased C128 ROM Update
The C128 source dump over at zimmers.net that appeared recently contains source for a version 2 kernel, which was never released. The known versions are 0 and 1. Let’s see whether we can reconstruct the ROM image!
Original Commodore Source Code Collection
Over the years, the ROM source code of many Commodore computers and peripherals has appeared. I have been collecting them in a git repository here:
Commodore Peripheral Bus: Part 3: Commodore DOS
In the series about the variants of the Commodore Peripheral Bus family, this article covers the common layer 4: The “Commodore DOS” interface to disk drives.
Commodore Peripheral Bus: Part 2: Bus Arbitration, TALK/LISTEN
In the series about the variants of the Commodore Peripheral Bus family, this article covers the common layer 3: the bus arbitration layer with the TALK/LISTEN protocol.
Commodore Peripheral Bus: Part 1: IEEE-488
In the series about the variants of the Commodore Peripheral Bus family, this article covers the lowest two layers (electrical and byte transfer) of the IEEE-488 bus as found on the PET/CBM series.
Commodore Peripheral Bus: Overview
The well-known Serial Bus (aka Serial “IEC” Bus) of the Commodore 64 that connects to disk drives such as the 1541 is just one variant of a whole family of busses and protocols used by the line of 8 bit Commodore machines from the PET to the C65. This is the first article of a multi-part series on the Commodore Peripheral Bus family.
Das neue Commodore 64 Intern Buch [PDF]
Announcement: The Ultimate Mars Rover Onboard Computer Talk
Daniel Jilg will present “The Ultimate Mars Rover Onboard Computer Talk”, the 7th talk in the “Ultimate Talk” series, at the 35th Chaos Communication Congress (35C3) on 2018-12-29 at 19:10 CET.
Archiving C64 Tapes Correctly
It’s pretty simple to archive Commodore 64 tapes, but it’s hard if you want to do it right. Creating the complete archive of the German “INPUT 64” magazine was not as easy as getting one copy of each of the 32 tapes and reading them. The tapes are over 30 years old by now, and many of them are hardly readable any more.