LANs in the ADN Public Labs

It is the use of LAN technology that enables us to maintain our public personal computer labs with our small staff. Each of the Computer Center labs on campus is actually a LAN that connects to the campus backbone network via a specialized device called a router. In effect, the ADN-ii backbone is a super-LAN (an internet) that has multiple LANs connected to it.

The computers in the ADN public labs do not boot from their hard disk drives like conventional personal computers do; in fact, they don't even have real hard disk drives. Instead, each computer has a special chip on its network card that can communicate with a remote file server and can download a copy of the operating system to the lab machine. (This is called "remote booting". )

Thus a fresh and consistent copy of the operating system is used each time the computer is booted. This virtually eliminates the threat of virus infection from the promiscuous interaction with a previous person's data, and will fix just about every software problem the computer could have, regardless of what any previous user of the machine did wittingly or unwittingly. This feature alone saves a huge amount of staff time that would otherwise be devoted to repairing software configurations on hundreds of lab machines.

When you turn on a machine in the labs, be it a Mac or a PC, it sends out a request for services from any available server. Generally, the least busy server will answer the request the first; your Mac or PC is then adopted by that server until you turn your machine off or reboot it. This scheme provides some automatic load balancing, virtually guaranteeing that you will connect to the server with the best response time at the time you connect.

Although none of the lab machines actually have a physical hard disk, the LAN connection and file server simulate several hard drives for them. The lab PCs see DOS software on drive S:, and Windows software on drive W:. The Macs see the software from the ADN_CC_MAC volume on their desktop. Other simulated hard disks, such as drive C: on the DOS and Windows PCs, can be used for temporary space. This space disappears when the machine is turned off and is wiped clean before reuse (which, among other things, protects your privacy), and it is a convenient place to store temporary files while working on a project, but you must save your files on your own diskette to keep them.

As part of booting the operating system (PC-DOS or Mac System 7.0), the lab machines load the LAN software from the file server. This software enables the machine to maintain a permanent connection to the file server for the duration of the session. The computer can then use all of the resources provided by the file server, including disk space and printers.

Just as we share disk drives and software, we also share printers. The machines in the labs print to a virtual printer on the LAN print server, which then sends the output to the real printer. These virtual printers are seen by the DOS and Windows machines as LPT1 (the standard DOS printer) and by the Macintoshes as the default printer queue. Like the Computer Center's CMS and UNIX systems, the LAN print servers use IP protocols to send the files over the ADN-ii network to the printers. This manner of printing lets us share printers between our larger systems and the microcomputers. It also allows any computer in a public microcomputer lab to print to printers in other public labs.