In addition, networks now include many other services (described below and in the next Bulletin) that work just like file and print services. All these functions have one distinguishing characteristic: unlike application services that involve multi-user databases, these functions all support individual users in performing individual personal productivity tasks.
Thus, file services allow users to save and retrieve documents on shared disk drives, just the same as if they were on their own computers. Print services work similarly, allowing users to select any printer connected to the network (e.g., a color printer for color documents, an ultra-high-speed printer for long reports, etc.) and print on them the same way they'd use a printer on their own PC.
These file and print services require coordination and, in a server-based network (see Bulletin 96.2), this coordination is done by a file server.
These applications are different from the single-user functions supported by the file and print services. Because they often require several users to access a single record simultaneously (for example, one user could be selling a product while another user is receiving new inventory of that same product). That's why these applications have traditionally run only on mainframe and mid-range computers that have built-in software to prevent data access conflicts between users.
Today, this kind of software runs on application servers, which may be the very same mainframe and mid-range systems they were running on before (only now, they're called "servers", not "central computers", because they're connected to networks). Why, one might ask, can't file servers be used for this purpose? Well they can, actually, but network operating system software designed to provide file and print services (like Novell's Netware) doesn't handle the data conflicts well or run efficiently, particularly in larger networks. On the other hand, operating systems designed for multi-user applications (such as Microsoft's NT-Server and UNIX) do a terrific job as application servers, but are much less effective at providing file and print services (particularly for multi-facility wide area networks). That's why many businesses are now using both: file servers for file and print services, and application servers to support their business-oriented applications.
Compaq and Hewlett-Packard are probably the most notable manufacturers specializing in building server computers. Although these machines generally cost two to four times as much as a normal PC built up to the same capacity, network managers have found that the "life cycle" cost of using them- figuring in maintenance costs, saved down time, and future upgrades and replacements- is less than using built-up PCs for that purpose.
Besides the functions described above, tremendous demand has built up for three other network services: outbound fax, shared access to CD-ROM-based reference materials, and inbound/ outbound data communications. All three of these functions have a greater similarity to file and print services than to application services, so they're most often performed by the file server or an auxiliary server using the file server's network operating system.
Networks can actually do both inbound and outbound faxing, but most only provide outbound fax services. That's because there's no great advantage to having the network receive inbound faxes; someone still has to look at them, figure out to whom they're addressed, and distribute them (just as they would with a paper fax). Network-based outbound faxing, on the other hand, provides three major benefits over conventional faxing:
Either the file server or a separate fax server can "host" the fax server software. Because fax services require significant processing power (to convert the document into an image of black and white dots called a "bit map") file servers shouldn't be used for this purpose except in small networks (of, say, 30 users or less) that seldom use fax capability for more than an hour or so a day. Larger networks should have a separate fax server with about the same power and capacity as a user computer, which can support two or more outbound fax lines, if justified, to support the fax traffic.
Another special purpose service is access to reference materials on CD-ROM. Every server computer and nearly all PCs and Macs today come equipped with a CD-ROM drive, so the solution to this need may seem like a "slam dunk" . . . it isn't. In an office environment, several people normally need to use the same CD-ROMs, often simultaneously. The file server's CD-ROM drive is fine for this, but the network administrator occasionally needs to use that drive and, when this happens, it must take first priority. The drives on individual users' computers create an even greater problem. Only one person can use a given CD at a time, and if usage isn't tracked rigidly, specific CDs can be very difficult to locate when they're needed.
There are two good ways to meet this need: a stack of fixed CD-ROM drives (usually attached to the file server) for the CDs that get constant usage and a CD-ROM "juke box" for the ones that are needed less often. Juke boxes vary in size from 4 to 50 CDs, and can "play" up to three of them at a time. With a mix of fixed drives and a juke box, users on the network don't need to know where CDs are; they just look up whatever data they want and the network CD-ROM services will retrieve it automatically. The only thing they'll notice is that if the CD they need is on a juke box, and isn't "mounted" when they call for it, it'll take a few extra seconds to retrieve their data. While this approach is slower than having everything on fixed drives, it's still much faster than keeping the CDs on a bookshelf (even a bookshelf at the user's desk) and having to mount them manually every time they're needed.
The third common network service is shared data communications, and this will be covered in the next Bulletin.
Mail to: brooks@bizauto.com with any questions or comments