A fax modem is an electronic device that transmits documentation to a fax machine or modem. Like data modems, fax modems are installed via motherboard, external Universal Serial Bus (USB) or parallel port. A fax modem card is a credit card-sized device and part of the Personal Computer Memory Card International Association (PCMCIA) family. A fax modem card is also known as a PC card.
Techopedia explains Fax Modem
Fax modems are delineated as follows: Class 1: Transmission time is six minutes or less. Inexpensive version connects to a personal computer (PC) and sends data as block frames only. No frame multitasking. Aborts during busy signals. Slowest versions transmit analog data. Class 2: Transmission time is two minutes or less. Connects to a PC or other enabled device. Organizes data by software session that receive modem commands for transfer. No frame transmission. Handles multitasking. Classes 3 and 4: Transmission time is 10 seconds or less. Most common versions that function without computer and/or software. Ideal for multitasking and email. Less expensive than class 2 and do not require bulky equipment. Fax modem cards are typically preinstalled, enable machine data portability and do not require fax modems. Internal 56k versions are the most common fax modem cards.