when apple introduced the laserwriter, its very high cost meant that the only cost-effective way to use it was shared among a small workgroup of macintoshes. this necessitated the inclusion of appletalk, a simple networking implementation which used low-cost cabling and the same physical rs-422 serial port hardware. it was a natural extension of "choose printer" to include the ability to select the laserwriter and also which port was used to connect its network connection.