[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.