Footnotes

1. This is the machine everyone always called the "breadbin" or "breadbox".
2. Filtering circuitry improved with the 8580 SID.
3. Cassette port was removed and ROM was updated in this unit to set the default device to 8 (the built-in 1541).
4. In C128 mode, the built-in 1571 becomes the default LOAD device. All modes on the VIC-IIe are identical to the C64 except that a few more tricks are possible using ~2MHz "Fast" mode. The VDC's modes are mildly extendable and mostly don't require active software tricks.
5. In C128 mode, the built-in 1571 becomes the default LOAD device. All modes on the VIC-IIe are identical to the C64 except that a few more tricks are possible using ~2MHz "Fast" mode. The VDC's modes are mildly extendable and mostly don't require active software tricks.
6. In C128 mode, the built-in 1571 becomes the default LOAD device. All modes on the VIC-IIe are identical to the C64 except that a few more tricks are possible using ~2MHz "Fast" mode. The VDC's modes are widely extendable and mostly don't require active software tricks.
7. The SX-64's power supply is generally considered to be irreplaceable, unlike the regular C64 and C64c's power supply. Therefore, due to it's low power output, the SX is not suitable for use with a SuperCPU or a Commodore 17xx REU, due to the power needs of those devices. The CMD RAMLink and RAMDrive can be used, however, as they have their own separate power supplies.
8. I have no clue what to put here. Can the C64C and/or the SX-64 be upgraded internally like the breadbox and the C128's?
9. All machines feature a VIC-II, and on this chip most video modes can be either altered or completely redesigned. A large number of extended video modes are possible using software tricks.
10. 16 KB VDC machines can be upgraded to 64 KB using a plug-in module or a permanent modification.
11. In the C64, the VIC-II has 1024 nybbles of memory dedicated to it, for color information in certain modes, plus the VIC-II uses up to 16 KB of base memory (configurable by the programmer).
12. Like the C64, the VIC-IIe uses a dedicated color RAM chip plus part of base memory, plus there is an extra register in the machine that controls which of the two 1024-nybble segments of color RAM is visible to the VIC. The VIC-II can also access, via a register, the entire 128 KB address space of the C128, and presumeably all the way up into the 1 MB that is possible with internal memory hacks.
13. All C64 and C128 computers feature one SID chip. Depending on whether you're upgrading a C64 or a C128, and the method used to add more SID chips, anywhere from two (six extra voices) to thirty-one more SID chips (that is, * 93 * extra voices) can be added to the machine, with only a small amount of basic glue logic and some perfboard. It is more practical to stop at 8 chips (to keep the I/O usage to one page), but in practice most users either stick with the single on-board SID, or they add one via a plug-in cartridge (total of 6 voices). At this time, I don't know of any software that supports more than two SID chips in a machine.
14. The VDC can do color cell sizes from 8x2 to 8x32 without software tricks. With a software trick similar to opening the upper/lower border on the VIC-II, the VDC can display 8x1 color cells.

Adding a SuperCPU to the mix introduces a number of changes to the way the machines operate. There were several other accellerators for the C64 over the years, but today only the SuperCPU really survived. Briefly, these changes are:

• The SuperCPU is an almost entirely self-contained computer, which runs at 20 MHz. Leaving the C64 or 128 to run internally at its normal ~1 MHz or ~2 MHz mode, the SuperCPU uses the C64/128 as essentially an I/O adaptor and video RAM.
• The SuperCPU runs at 20 MHz unless software instructs it to communicate with video RAM or I/O devices, or tells it to manually slow down to match the C64.
• The SuperCPU employs a one-byte write cache, allowing it to disconnect from the C64 entirely. This allows the programmer to perform a write operation and then immediately go do something else, without waiting, while the cache handles the actual write operation to I/O or video RAM. This applies so long as the programmer spaces his/her writes out so that they occur at least 20 cycles apart.
• The SuperCPU always slows down when reading from an I/O device, and does not use the cache.
• The write cache allows SuperCPU code to treat the C64 as a ~1 MHz I/O and video memory bus. This allows more video and sound effects than the C64 would normally be capable of (you can normally write to memory or I/O at about 50 KB/sec).
• The WDC 65816 used in the Super CPU does NOT support the 6502's so-called "illegal" opcodes. Instead, the command set has been extended.
• In exchange for those "illegal" opcodes, most of the 6502's instructions have been upgraded to allow them to take advantage of the full 16 MB of available memory, if present.
• The SuperCPU comes with 256 KB of 20 ns "cache" RAM, which serves as base memory. User-installed extended memory beyond this is 70 ns or faster.
• In 20 MHz mode, the SuperCPU corrects for the 70 ns speed by imposing occasional memory wait states when dealing with extended memory. On average, these wait states incur up to a 5% speed penalty. It is possible to avoid wait-states with carefully written code.
• With Turbo mode turned off, code runs at the same speed as on stock machines, wherever it is located in the 16 MB address space, and perform block-move commands at a rate of seven clock cycles per byte, regardless of which part of memory that's being dealt with.
• With Turbo mode turned on, block-moves to the first 256 KB are executed at 7 cycles per byte, and code in this region runs at about 2.71 Million to 10 Million instructions per second.
• Internal memory hacks that take the C64 or C128 beyond 64 or 128 KB are not recognized by the Super CPU.