 Internal modems could be software controlled to perform both outbound and inbound calls, but external modems had only the data pins to communicate with the host system.
<fluency>  Internal modems could be software controlled to perform both outbound and inbound calls, but external modems had only the data pins to communicate with the host system.
 Internal modems could be software-controlled to perform both outbound and inbound calls, but external modems had only the data pins to communicate with the host system.