[leptons]

I built my own 300bps modem as a teenager, to connect to my C64. Tech was a lot more fun back in the day. It was exciting every year to see the speed of modems go up, and up, and up. 300 bps, 1200bps, and then when I got a 2400bps modem the C64 built-in serial code was too slow, I couldn't transfer files because there were so many dropped bits. So I wrote my own serial port code in assembly language and hacked it into my favorite terminal software (CCGMS) and that fixed the problem. I think by the time I got a 9600 baud modem I probably had an Amiga.

[jandrese]

By the time you get to 2400bps you're starting to stress how fast the abysmal disk interface on the C64 could write data, you had better not hit too many seeks.

[leptons]

The 1541 drive can write at ~400 bytes per second, much faster than the 2400bps modem could deliver (240 bytes/s). And buffering was a thing back then. A simple ring buffer would suffice. I had no problems downloading at 2400bps after I fixed the serial code.

[jandrese]

Faster, but not "much faster". Depending on where you were writing it could be as low as 300 bytes/second. You're starting to cut close to the margins, especially if the C=64 is having to also manage the modem communications at the same time. So yeah, doable but that's about the max you can expect out of the hardware. A 4800 baud modem would be right out.

[leptons]

The C64 doesn't control the disk drive directly, the 1541has its own CPU, about as powerful as the C64.

> A 4800 baud modem would be right out.

Not with a "Warp Speed" cartridge. It does write speeds on a stock C64/1541 up to 2900 Bytes per second. I'm pretty sure reading serial data faster than 2400bps is easily doable too.

https://www.obliterator918.com/the-warp-speed-cartridge-from...

[rasz]

Modern 1541 turbo, like Krills Transwarp, tops out just shy of 20KB/s on unmodified hardware https://csdb.dk/release/?id=214786 with steady 16KB/s in normal use https://www.obliterator918.com/benchmarking-transwarp-the-in... The trick is encoding files in special way to minimize drives CPU load.

[joquarky]

CCGMS was the best.