Visualizing Commodore 1541 Disk Contents – Part 2: Errors
We have previously visualized the physical layout of C64/1541 disks. In order to understand the encoding and potential read errors, it is more useful to visualize the disks sector-by-sector.
Dumping Commodore 64/1541 Disks with Errors
Many old Commodore 64/1541 disks have read errors, but this doesn’t mean the data isn’t recoverable – with the right nibtools settings and some cleaning.
Converting a Commodore 1541 or 1570 Drive into a 1551
The 1551 is the weird outlier in the family of Commodore disk drives: It is the only drive using the “TCBM” bus instead of Serial or IEEE-488. And what’s even weirder? 1541 and 1570 drives converted into 1551s!
More Original Commodore Source Code
There have been a few new interesting additions to the Commodore Source Code repository, including:
Commodore Peripheral Bus: Part 5: TCBM
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 “TCBM” bus as found on the TED series computers: the C16, C116 and the Plus/4.
Blue Chip BCD/5.25 Disk Drive
After previously dissecting the firmware of alternate C64 disk drives, let’s now look at the hardware of one: This is the Blue Chip BCD/5.25.
Recovering Files from Broken Amiga OFS Disks
extract-adf is a tool for recovering files from broken Amiga OFS filesystem images. It can reconstruct directory hierarchies even for files that don’t have directory entries.
The Commodore IEEE-488 Cartridge for C64
Commodore 64 disk drives were usually connected through the slow serial bus. This article shows some hi-res photos of the Commodore “IEEE-488 cartridge”, which made the faster PET drives available for the C64.
Commodore Peripheral Bus: Part 4: Standard Serial
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 “Standard Serial” bus as found on the VIC-20/C64 as the main bus, but also supported by all other Commodore home computers.
The Commodore 8250 Dual Drive Floppy Disk
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.
Third Party Disk Drives for the C64: The “Technica”
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.
Reconstructing the GEOS 2.0 (de) Master Images from a Pile of Broken Disks
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.
A GEOS Speed Zone Bug? (Why Do C64 GEOS Boot Disks Break, Part 2)
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!
Why Do C64 GEOS Boot Disks Break? (Part 1)
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.
Reading the Raw Bits of a C64/1541 Disk without a Parallel Cable
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.
Making of the Book “Anatomy of the 4040 Disk Drive”
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.
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.
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 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:
