Commodore’s “Inner Space”
No other computer has achieved the cult status the Commodore C64 has. Its sales totaled 17 million units, making it the best-selling single personal computer model of all time, and it was the machine that got many of us interested and involved in the whole IT industry.
Whereas most of us have used it to play and learn to program, it was only those that used it to experiment with electronic circuits and robotics, that dared to open the plastic case and take a look at what’s inside…
I recently was asked by @digger_c64 if I could upload some pictures of the internals of the C64s I have in my collection. A great idea and I’ll do one better: Today I’ll be taking a look at the inside of 5 “types” of C64: the original breadbox, the C64C, the C64G, the C64 “Aldi” and the SX-64 and guide you through the evolutions, differences and oddities.
So sit back and relax while I take you on a trip in Commodore’s “Inner Space”. (Oh, and you can get bigger images by simply clicking the smaller image – the really big images can be found on my Flickr! page, in the set “Commodore 64 Internal”).
The picture below shows the mainboard of a classic breadbox Commodore C64. You can recognize these boards by the “PCB ASSY #250407” assembly number. It is not the first type of the C64’s mainboards, but one that it is pretty mainstream. The older mainboards like the “Revision A”, (they tend to differ depending wether it was a US, UK or West-German model) were found in the very first C64s, with the silver logo and have become quite the collectible item (yes, it’s on my “Most Wanted” list for my collection this year). Several chips show the 1982 date on these old “Silver Label” boards.
Now, most of us know about the 6510 CPU and the SID chip, but where exactly where these to be found on the mainboard? I’ve highlighted the different components on the pictures, with the main ones highlighted.
There’s also a Revision B and C, both found in the breadbox C64 as well. The biggest difference in these two revisions is that the SID and PLA have swapped places.
On to the C64C. This Commodore 64 features the 128/Amiga-styled casing and on the inside has the components in the same locations as on the original mainboard, except for the fact that it had two chips making up the 64K of RAM, instead of the 8 previously.
Note that the SID and PLA have switched places! It is also the C64 model – apart from the SX-64 - that takes the most time to disassemble as keyboard and metal heatsink need to be removed before it will show its mainboard.
The board has the 250466 assembly number.
Next up, we have the C64G. This system was the first to introduce a new main board (assembly number 250469 – multiple revision numbers exist) which is considerably smaller in size. It came housed in the traditional breadbox casing.
It features the new 8500 CPU, which is the HMOS version of the 6510 CPU and some components such as one of the CIAs, the keyboard connector and the Character ROM have moved.
Further changes are:
- New SID chip, the 8580
- New VIC, the 8565
- Integration of the BASIC and KERNAL in a single ROM, the 251913, known as the Memory Management Unit (MMU)
- PLA integrated with several TTL chips in a single 64-pin IC (LH5062)
Let’s move on to the C64 “Aldi”. It is a pretty elusive version of the C64, a rarity even, as it was only released in Germany through the discounter “Aldi”.
What makes this release special is the fact that it is a merger of worlds, the “old” and the “new”: it’s made up of the old bread-bin case together with the smaller motherboard of the C64G models. Furthermore, it features white/ivory keys (as on the C64C) instead of the classic brown C64-keys.
On the inside, it’s the C64G motherboard (the 250469 – Rev.3) but it lacks the 9 Volt on the User Port (pins 11 and 12). This made it impossible to connect it to an EPROM burner.
I marked the missing 9 Volt connector on the picture (on the other mainboards, the drill holes on the PCB are “filled”, connecting them to the 9 Volt of the board).
Last but not least, we have the Commodore SX-64. It was the first portable color computer in the world, and as such, it features a 1541-drive and a color monitor on the inside (as well as the heavy power-supply). This means that the mainboards for both C64 and 1541 are present on the inside. The design called for the mainboard of the C64 to be modified to fit into the casing, with the Expansion Port on the top of the computer.
Another big difference was that it did not feature a Datasette port.
Taking a peek is quite an undertaking as a lot of screws have to come out first. The inside of this legendary machine though is quite the sight and it features its own custom mainboards for the computer and drive along with a separate board for the different connectors and a small board for the Expansion Port. Basically, they took the C64 board, and divided it into a CPU-board and an I/O-board.
The pictures below show the different boards with the CPU board boasting the SID and PLA.
So, there we have it, an overview of the different C64 boards to be found. There is one mainboard missing from the overview, and that’s the mainboard of the C64GS (the game console version of the C64). This one’s also high on my “Most Wanted” list, so as soon as this one is added to the collection, expect an update to this article!