Some Assembly Required
The GEOS operating system for the Commodore 64 achieved to replicate much of the GUI of the original Macintosh on a 1 MHz 8 bit CPU with just 64 KB of RAM. The GEOS Demo is a presentation by Berkeley Softworks (BSW), the creators of GEOS, to showcase the features of GEOS and BSW’s applications.
The Commodore 8250 was the high-end 5.25″ disk system for the Commodore PET, with two drives that could each fit 1 MB (4133 blocks free) on a standard disk. Here are some high-res pictures.
This is the previously unpublished “Commodore 264 Series Preliminary Users Manual”, a prerelease version of the manual of what came to be the Commodore Plus/4.
Here are some hi-res photos of the Commodore 232 and Commodore 264 prototypes. The C-232 and C-264 were two1 of the planned models of the TED series, but neither shipped. The C-264 became the Plus/4, with productivity software preinstalled in ROM, and the low-lost C-232 was replaced by the even lower-cost C16 and C116 models.
I have previously analyzed the ROM images of some third party disk drives for the Commodore 64: The result was that most of them were just using the original binaries with some obfuscation, and some with some added features. This time, let’s look at another drive, the “Technica”, which is a little special in this regard.
I have this pile of broken GEOS disks that were sent in for replacements. In two previous articles (1, 2), I explored the reasons why the disks broke. Now let’s be constructive: Can we reconstruct the original bits by combining the correct parts? This article shows how it is possible with the help of a small tool that combines the good parts of several broken disk images.
The original Commodore 64 KERNAL and BASIC source code has been available for a while. It used to be built using Commodore’s assembler of a PET.
I happened to come across 50 original German GEOS 2.0 disks that were broken and sent in for replacement. In the first part, I covered the disks that were broken probably due to user error. Now let’s look at the read errors on the remaining disks. As it turns out, there might be a bug in GEOS that caused the boot disks to break!
The most fragile things in the universe (next to C64 PLA chips) are C64 GEOS boot disks. Because of its copy-protection, the “Graphic Environment Operating System” had to be booted from the original disk every time. The disk failed so often that the box came with a second “backup” boot disk.
An unmodified Commodore 1541 disk drive cannot transfer the raw bits of a whole track to the computer it is attached to: The Commodore Serial Bus is too slow to transmit the data in real time as it arrives from the read head, and the drive only has 2 KB of RAM, which is not enough to buffer the 8 KB of a whole track.
To my surprise, Hilaire Gagne, the author of “Anatomy of the 4040 Disk Drive”, commented on my blog post about the reconstruction of his book.
An empty ribbon of the 9-pin printer Commodore MPS 1550 C (which is mechanically identical with the Olivetti DM 105) can easily be refilled using stamp pad ink. Here is how:
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.
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:
My side-by-side C64 ROM disassembly/commentary page has been completely redone!
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!
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.
You might think the DOS ROM of the Commodore 1541 disk drive has been analyzed to death. But here are two new resources:
