The 3Com 3Server was a headless dedicated network-attached storage machine designed to run 3Com local area network (LAN) server software, 3+Share.
Having no display other than a small one-line LCD and no keyboard or mouse interface, 3Servers were controlled via another PC on the network which allowed console access to the internal server software.
The original 3Server was a x86 computer that wasn't compatible with any ordinary PC based on an Intel 80186 CPU, running a special version of MS-DOS and 3Com's proprietary 3+Share network server software.
Internally, it had a network stack, file and print server modules, disk caching, user handling and more, all running simultaneously inside the DOS memory space.
3Com's version was an enhancement of the basic LAN Manager package, also sold by Microsoft and IBM and on other operating systems - for example, running on VAX/VMS it was the basis of DEC Pathworks.