The modem (short for modulator-demodulator) is used for the digital remote data transmission (short: RDA) between computer systems (like clients or servers) and networks (like internet, etc.) over the telephone wire (like analog, ISDN, DSL, etc.). Computer systems can connected with internal or external modems to other computers. On the C64/128 is used an external modem cartridge.
In the 1970's and 1980's another type of modem was the acoustic coupler.
The speed of the data transfer is baud (short: bd) or bit per seconds (short: bps, bit/s). A baud is similair one bit. Another unity of data transfers is byte/s, which is confuse with bit/s.
Additional are listening BTX cartriges.
Commodore produced this modems:
- Commodore / CBM 1650 "Automodem" (300 bd) for C64 and VIC-20
- Commodore 300 bzw. CBM 1660 (300 bd, year 1985) for C64
- Commodore / CBM 1064]
- Commodore 1200 bzw. CBM 1670 (1200 Bd, year 1987) for C64
- CBM 1670CR (1200 bd, year 1987) for C64
- Commodore / CBM 1680 modem (1200 Bd) for Amiga
- Commodore / CBM 6499 (300/300 and 1200/75 bd Btx) for C64
- Commodore VM 2400 (2400 bd)
- CBM 8010 (300 bd) for CBM
- VIC 1600 and 1605 (300 bd)
- BTX modul V1, V2
- Modem C64+
- 64'er online (Drews EDV+Btx GmbH)
- BTX-Com (Digitec-Saarbrücken)
- Quick Silver 64/128 (Skyless Electric Works)
- VIC REL (VIC-20, C64), Handic Software AB, 1983