Thursday, December 28, 2023

Using my Commodore 64 and 128 in 2023

Two years ago, I wrote a blog post about using my Commodore Amiga 500 in 2021 after not having touched it in ten years. Although the computer was still mostly functional, some peripherals were broken.

To fix my problems, I brought it to the Home Computer Museum in Helmond for repairs.

Furthermore, I have ordered replacement peripherals so that the machine can be more conveniently used, such as a GoTek floppy emulator. The GoTek floppy emulator makes it possible to conveniently use disk images stored on an USB memory stick as a replacement for physical floppy disks.

I also briefly mentioned that I have been using my first computer: a Commodore 128 for a while. Moreover, I also have a functional Commodore 64, that used to be my third computer.

Although I have already been these 8-bit machines on a more regular basis since 2022, I was not satisfied enough yet to write about them, because there were still some open issues, such as a broken joystick cable and the unavailability of the 1541 Ultimate II cartridge. The delivery took a while because it had to be redesigned/reproduced due to chip shortages.

A couple of weeks ago, the cartridge was finally delivered. In my Christmas holiday, I finally found the time to do some more experiments and write about these old 8-bit Commodore machines.

My personal history

The Commodore 128, that is still in my possession, originally belonged to my parents and was the first computer I was exposed to. Already as a six year old, I knew the essential BASIC commands to control it, such as requesting a disk's contents (e.g. LOAD"$",8: LIST), loading programs from tape and disk (e.g. LOAD, LOAD"*",8,1) and running programs (RUN).

One of my favorite games was the Commodore 64 version of Teenage Mutant Ninja Turtles developed by Ultra Software, as can be seen in the above screenshot.

I liked the game very much because I was a fan of the TV show, but it was also quite buggy and notoriously difficult. Some parts of the game were as good as impossible to finish. As a result, I was never able to complete the game, despite having played it for many hours.

Many relatives of mine used to have an 8-bit Commodore machine. A cousin and uncle used to own a Commodore 64C, and another uncle owned a Commodore 128. We used to exchange ideas and software quite a lot.

At first, I did not know that a Commodore 128 was a more capable machine than an ordinary Commodore 64. My parents used to call it a Commodore 64, and for quite some time I did not know any better.

The main reason behind the confusion is that a Commodore 128 is nearly 100% backwards compatible with a Commodore 64 -- it contains the same kinds of chips and it offers a so-called Commodore 64 mode.

You can switch to Commodore 64 mode by holding the Commodore logo key on bootup or by typing: GO64 on the command prompt. When a utility cartridge is inserted, the machine always boots in Commodore 64 mode. The picture above shows my Commodore 128 running in Commodore 64 mode.

At the time, we had a utility cartridge inserted into the cartridge socket that offered fast loading, preventing us from seeing the Commodore 128 mode altogether. Moreover, with the exception of the standard software that was bundled with the machine, we only had Commodore 64 software at our disposal.

In 1992, I wrote my first BASIC program. The program was very simple -- it changes the colors of the text, screen and screen border, asks somebody to provide his name and then outputs a greeting.

At some point, by accident, the utility cartridge was removed and I discovered the Commodore 128 mode, as can be seen in the picture above. I learned that the Commodore 128 ROM had a more advanced BASIC version that, for example, also allows you to play music with the PLAY command.

I also discovered the CP/M disk that was included with the machine and tried it a few times. It looked interesting (as can be seen in the picture above) but I had no applications for it, so I had no idea what to do with it. :)

I liked the Commodore 128 features very much, but not long after my discovery, my parents bought a Commodore Amiga 500 and gave the Commodore 128 to another uncle. All my relatives that used to have an 8-bit Commodore machine already made the switch to the Amiga, and we were the last to make the transition.

Although switching to a next generation machine may sound exciting, I felt disappointed. In the last year that the Commodore 128 was still our main machine, I learned so much, and I did not like it that I was no longer be able to use the machine and learn more about my discoveries. Fortunately, I could still play with the old Commodore 128 once in a while when we visited that uncle that we gave the machine to.

Some time later, in late 1993, my parents gave me a Commodore 64 (the old fashioned breadbin model) that they found at a garage sale (as shown in the picture above). This was the third computer model that I was exposed to and the first computer that was truly mine, because I did not have to share it with my parents and brother. This machine gave me my second 8-bit Commodore experience, and I have been using this old machine for quite some time, until mid-1997.

Originally, the Commodore 64 did not come with any additional peripherals. It was just the computer with a cassette drive and no utility cartridges for fast loading. I had a cassette with some games and a fast loading program that was the first program on the tape. Nothing more. :)

I was given a few books and I picked up Commodore 64 programming again. In the following years, I learned much more about programming and the capabilities of the Commodore 64, such as for-loops, how to do I/O, how to render sprites and re-program characters.

I have also been playing around with audio, but my sound and music skills were far too limited to do anything that makes sense. Moreover, I did quite a few interesting attempts to create games, but nothing truly usable came out of it. :)

In 1994, I bought a 1541 disk drive and several utility cartridges at a garage sale, such as the Final Cartridge (shown above). The Final Cartridge provides all kinds of useful features, such as fast loading and the ability to interrupt the machine and inspect its memory with a monitor.

Owning a disk drive also allowed me to make copies of the games that I used to play on my parents' Commodore 128.

Eventually, in 1998 I switched to the Commodore Amiga 500 as my personal machine, but I kept my Commodore 64. In 1998, Commodore was already out of business for four years and completely lost its relevance. My parents bought a PC in 1996. After using the Amiga for a while on the attic, the Amiga's display broke rendering it unusable. In 1998, I discovered how to attach the Amiga to a TV.

In late 1999, I was finally able to buy my own PC. I kept the Amiga 500, because I still considered it a cool machine.

Several years later, the Commodore 128 was returned to me. My uncle no longer had any use for it and was considering to throw it away. Because I still remembered its unique features (compared to a regular Commodore 64), I have decided to take it back.

Some facts

Why is the Commodore 64 such an interesting machine? Besides the fact that it was the first machine that I truly owned, it has also been listed in the Guinness World Records as the highest-selling single computer model of all time.

Moreover, it also has interesting capabilities, such as:

  • 64 KiB of RAM. This may not sound very impressive for nowadays' standards (for example, my current desktop PC has 64 GiB of RAM, a million times as much :) ), but in 1982 this used to be a huge amount.
  • A 6510 CPU, which is a modified 6502 CPU that has an 8-bit I/O port added. On machines with a PAL display, it runs at a clock speed slightly under 1 MHz.
    Compared to modern CPUs, this may not sound impressive (a single core of my current CPU runs at 3.7 GHz :) ), but in the 80s the CPU was quite good -- it was cheap and very efficient.

    Despite the fact that there were competing CPUs at the time that ran at higher clock speeds, most 6502 instructions only take a few cycles and fetch the next instruction from memory while the previous instruction is still in execution. As a result, it was still a contender to most of its competitors that ran at higher clock speeds.
  • A nice video chip: the VIC chip. It supports 16 preconfigured colors and various screen modes, including high resolution screen modes that can be used for addressing pixels. It also supports eight hardware managed sprites -- movable objects directly controlled by the video chip.
  • A nice sound chip: the SID chip. It offers three audio channels, four kinds of waveforms (triangle, sawtooth, squarewave and white noise) and analog mixing. This may not sound impressive, but at the time, the fact that the three audio channels can be used to mix waveforms arbitrarily was a very powerful capability.
  • An operating system using a BASIC programming language interpreter (Commodore BASIC v2) as a shell. In the 70s and 80s, BASIC was a very popular programming language due to its simplicity.

Other interesting capabilities of the Commodore 64 were:

  • The RAM is shared between the CPU and other chips, such as the VIC and SID. As a result, the CPU is offloaded to do calculation work only.
  • The CPU's clock speed is aligned with the video beam. The screen updates 50 times per second and the screen is rendered from top to bottom, left to right. Each screen block takes two cpu cycles to render.

    These properties make it possible to change the screen while it is rendered (a technique called racing the beam). For example, while the screen is drawn, it is possible to adjust the colors in color RAM, multiplexing sprites (by default you can only configure eight sprites), changing screen modes (e.g. from text to high res etc).

    For example, the following screenshot of a computer game called: Mayhem in Monsterland demonstrates what is possible by "racing the beam". In the intro screen (that uses multi-color bitmap mode), we can clearly see more colors per scanline than three unique colors and a background color per 8x8 block, that is normally only possible in this screen mode:

  • And of course, the Commodore 64 has a huge collection games and applications.

The Commodore 128 has similar kinds of chips (as a result, it is nearly 100% compatible with the Commodore 64).

It has the following changes and additions:

  • Double the amount of RAM: 128 KiB
  • A second video chip: the VDC chip, that can render 80-column text and higher resolution graphics, but no sprites. To render 80-column output, you need to connect an RGBI cable to a monitor that is capable of displaying 80-column graphics. The VDC chip does not work with a TV screen.
  • A CPU that is twice as fast: the 8502, but entirely backwards compatible with the 6510. However, if you use the VIC chip for rendering graphics (40 column mode) the chip still runs at half its speed, which is the same as the ordinary 6510. In 80-column mode or when the screen is disabled, it runs at twice the speed of a 6510.
  • A second CPU: the Zilog Z80. This CPU is used after booting the machine in CP/M mode from the CP/M boot disk.
  • An improved BASIC interpreter that supports many more features: Commodore BASIC v7.0

Using the Commodore machines

To conveniently use the Commodore machines in 2023, I have made a couple of repairs and I have ordered new peripherals.

Power supplies

I bought new power supplies. I learned that it is not safe to use the original Commodore 64 power supply as it gets older -- it may damage your motherboard and chips:

In a nutshell, the voltage regulator on the 5 volt DC output tends to fail in such a way that it lets a voltage spike go straight to your C64 motherboard, frying the precious chips.

Fortunately, modern replacement power supplies exist. I bought one from: that seems to work just fine.

I also bought a replacement power supply for the Commodore 128 from Keelog. The original Commodore 128 power supply is more robust than the Commodore 64 power supply, but I still want some extra safety.

Cassette drive

As I have already explained, my Commodore 64 breadbin model only included a cassette drive. I still have that cassette drive (as shown in the picture above), but after obtaining a 1541 disk drive, I never used it again.

Two years ago, I ordered an SD2IEC that included a bonus cassette with a game: Hi-Score. I wanted to try the game, but it turned out there was a problem with the cassette drive -- it seems to spin irregularly.

After a brief investigation I learned that the drive belt was in a bad condition. I have ordered a replacement belt from Ebay. Installing it was easy, and the game works great:

Disk drives

I have two disk drives. As I have already explained, I have a 1541 drive that I bought from a garage sale for my Commodore 64. The pictures above show the exterior and interior of the disk drive.

The disk drive still works, but I had a few subtle problems with running modern demos that concurrently load data while playing the demo. Such demos would sometimes fail (crash or the sound starts to run out of sync with the rest of the demo), because of timing problems.

I have cleaned the disk drive head with some alcohol and that seemed to improve the situation.

I also have a 1571 disk drive that came with the Commodore 128. The 1571 disk drive is a more advanced disk drive, that is largely backwards compatible with the 1541. The pictures above show the exterior and interior of the drive.

In addition to ordinary Commodore 64 disks, it can also read both sides of a floppy disk at the same time and use disks that are formatted to be as such. It can also run in MPM mode to read CP/M floppy disks.

My 1571 disk drive still seems to work fine. The main reason why I did not have to clean it is because I have not used it as much as the 1541 disk drive.

The 1541 and 1571 disk drives are interesting devices. They are computer systems themselves -- each of them contains two embedded machines each having their own 6502 CPUs. One sub system is responsible for managing filesystem operations and the communication with the main computer, while the other sub system is used for controlling the drive.

The 1541 disk drive contains 2 KiB of RAM and runs its own software from a ROM chip that provides the Commodore Disk Operating System.

Technically, using a disk drive on an 8-bit Commodore machine is the same as two computer systems communicating with each other over Commodore's proprietary serial interface (the IEC).


I also have a monitor for the Commodore 128 machine: the Commodore 1901 that is capable of displaying graphics in 40 and 80 column modes. It has an RGBI socket for 80-column graphics and RCA sockets for 40-column graphics. I need to use a switch on the front panel to switch between the 40 and 80 column graphics modes. In the picture shown above, I have switched the monitor to 80-column mode.

The monitor still works fine, but in 2019 a capacitor burned out, causing smoke to come out of the monitor, which was a scary experience.

Fortunately, the monitor was not irreparably damaged and the home computer museum managed to replace the broken capacitors. After it was returned to me, it seems to work just fine again.

In 1992, besides "The Very First": a programming tutorial and CP/M, I did not have any software for the Commodore 128. In the recent years I have downloaded a few interesting applications for the Commodore 128, such as a Tetris game that works in 80-column mode:


As already shown in earlier pictures, I am using The Arcade joysticks produced by Suzo International. I have four of them.

Unfortunately, three of them did not work properly anymore because their cables were damaged. I have managed to have them repaired by using this cable from the Amiga shop as a replacement.


The Commodore 128 also came with a 1351 mouse (a.k.a. tank mouse), but it was lost. I never used a mouse much, except for GEOS: a graphical operating system.

To get that GEOS experience back, I first bought an adapter device that allows you to use a PS/2 mouse as a 1351 mouse. Later, I found the same 1351 mouse model on Ebay:


I have also been looking into more convenient ways to use software that I have downloaded from the Internet. Transferring downloaded disk images from and to physical floppy disks is possible, but quite inconvenient.

The SD2IEC is a nice modern replacement for a 1541 disk drive -- it is cheap, it can be attached to the IEC port and all high-level disk commands seem to be compatible. Physically, it also looks quite nice:

As can be seen it the picture above, it looks very similar to an ordinary 1541 disk drive.

Unfortunately, low-level disk-drive operations are not supported -- some applications need to carry out low-level operations for fast loading, such as demos.

Nonetheless, the SD2IEC is still a great solution, because there are plenty of applications and games that do not require any fast loading capabilities.

1541 Ultimate II cartridge

After happily using the SD2IEC for a while, I wanted better compatibility with the 1541 disk drive. For example, many modern demos are not compatible, and I do not have enough physical floppy disks to store these demos on.

As I have already explained, this year, I have ordered the 1541 Ultimate II cartridge, but it took a while before it could be delivered.

The 1541 Ultimate II cartridge is an impressive device -- it can be attached to the IEC port and the tape port (by using a tape adapter) and provides many interesting features, such as:

  • It can cycle-exact emulate two 1541 disk drives
  • It offers two emulated SID chips
  • It can load cartridge images
  • It simulates disk drive sounds
  • You can attach up to two USB storage devices. You can load disk images and tape images, but you can also address files from the file system directly.
  • It has an ethernet adapter.

The above two pictures demonstrate how the cartridge works and how it is attached to the Commodore 64.

I am very happy that I was able to run many modern demos developed by the Demoscene community, such as: Comaland by Oxyron and Next level by Performers etc. on a real Commodore 64 without using physical floppy disks:


Sometimes I also want to transfer data from my PC to physical floppy disks and vice versa.

For example, a couple of years ago, I wanted to make a backup of the programs that I wrote when I was young.

In 2014, I have ordered a ZoomFloppy device to make this possible.

ZoomFloppy is a device that offers an IEC socket to which a Commodore disk drive can be connected. As I have already explained, Commodore disk drives are self-contained computers. As a result, linking to the disk drive directly suffices.

The ZoomFloppy device can be connected to a PC through the USB port:

The above picture shows how my 1541 disk drived is connected to my ThinkPad laptop by using the ZoomFloppy device. If you carefully look at the screen, I have requested an overview of the content of the disk that is currently in the drive.

I use OpenCBM on my Linux machine to carry out disk operations. Although graphical shells exist (for example, the OpenCBM project provides a graphical shell for Windows called: cbm4wingui), I have been using command-line instructions. They may look scary, but I learned them quite quickly.

Here are some command-line instructions that I use frequently:

Request the status of the disk drive:

$ cbmctrl status 8
73,speeddos 2.7 1541,00,00

Format a floppy disk (with label: mydisk and id: aa):

$ cbmformat 8 "mydisk,aa"

Transfer a disk image's contents (mydisk.d64) to the floppy disk in the drive:

$ d64copy mydisk.d64 8

Make a D64 disk image (mydisk.d64) from the disk in the drive:

$ d64copy 8 mydisk.d64

Request and display the directory contents of a floppy:

$ cbmctrl dir 8

Transfer a file (myfile) from floppy disk to PC:

$ cbmcopy --read 8 myfile

Transfer a file (myfile) from PC to floppy disk:

$ cbmcopy --write 8 myfile


In this blog post, I have explained how I have been using my old 8-bit Commodore 64 and 128 machines in 2023. I made some repairs and I have ordered some replacement peripherals. With these new peripherals I can conveniently run software that I have downloaded from the Internet.

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