Microcom 424 Operator's Manual page 176

USB (Universal Serial Bus) - A high-speed asynchronous serial interface that connects a
PC to a peripheral, such as a printer. There are 3 versions of USB:
1) USB 1.0 transfers at 1M bits/second. (Hardly used at all anymore).
2) USB 1.1 transfers at 12M bits/second. (The 324 & 424 printers use this).
3) USB 2.0 transfers at 480M bits/second. (All newer PC's use this).
12-20 224/424 Operator's Manual - 880027-1000