MacTCP

MacTCP was software developed by Apple Computer to provide TCP/IP networking support for classic Mac OS from System 6.0.3 and later. It was superseded by Open Transport in Mac OS 7.5.2.

Usage
Using MacTCP will cause a file named MacTCP DNR to appear in the top level of the System Folder. Though the Finder may identify this file as a control panel, it cannot be opened nor accessed through the vintage Control Panel desk accessory. This unopenable file is essential as it functions as a "domain name resolver" (DNR) for MacTCP. It is needed by certain Internet applications for TCP/IP access and should not be moved or deleted. This file is only needed if surfing around the web without Open Transport-compatible applications and using an Internet provider other than America Online. Any attempt at removing this control panel will result in it being recreated, the next time the Internet is accessed.