Expanded Memory: One Solution to Networked CD-ROM Memory Problems
The software needed to operate CD-ROM systems often requires a lot of random access memory (RAM) to function properly. This can be a problem for some systems and is compounded when CD-ROMs are used over a local area network (LAN). This article shows how the addition of an expanded memory card, an inexpensive piece of hardware, can help ease the memory shortage problem.
There is no doubt that CD-ROM will be a part of life in libraries for a number of years to come. In fact, the pressure is already on for a significant change in this technology -- the ability to network the CD-ROM products. It has become clear that long waits for access to a particular CD-ROM are not acceptable and that access to a CD-ROM product should not be limited to a single microcomputer. Several vendors have attempted to correct this problem by marketing systems that allow the CD-ROM drives (and the data they contain) to be shared by many workstations over a local area network.
The UNB Experience
In the summer of 1989, the University of New Brunswick Libraries received a grant from the university's Futures Fund to conduct a CD-ROM networking experiment at our campus. The system has been operational since early November of 1989. It consists of a Zenith 386 file server, IBMPCNET LAN software, OPTINET software, and six CD-ROM drives connected to the server. There are IBM PS/2 Model 25s built around the 8086 CPU located in each of the library system's four locations on campus. Broadband network cabling has been in place for several years.
There are any number of problems inherent in installing such a system. The possibilities for hardware and software conflicts between all the components are too numerous to calculate. In our system, they usually appeared as read errors from the discs. All were solved by experimentation and assistance from the vendor's technical support staff.
One problem that will not go away, however, is the shortage of usable RAM memory in the workstations accessing the CD-ROM drives. An expanded memory board is one solution to the problem. Following is a description of how one such product, an AMS Hicard2, can be used to resolve memory shortages.
The maximum amount of memory addressable by 8088 and 8086-based PCs is 1 megabyte. This is sometimes referred to as conventional memory. Even if your PC is equipped with 1 megabyte of memory, the amount between 640 kilobytes and 1 megabyte is not normally available for running programs, as this 384 kilobytes is reserved for peripherals. AT-class machines built around the 80286 chip can address memory above 1 megabyte called extended memory.
When expanded memory hardware and software device drivers are present, AT-class machines have access to extended memory and PCs can access unused higher conventional memory above 640 kilobytes.
In the early days of PC use, programs generally did not occupy as much RAM as they do now. The upper limit of 640 kilobytes was considered adequate. In the past few years, however, the programs have become much larger. One class of programs taking up a lot of RAM is the search software required to operate CD-ROM drives. If the computer does not have enough free RAM for the software, the system will not operate or will suddenly crash in the middle of a session.
It is unfortunate that when one attempts to operate CD-ROMs in a networking situation, the amount of RAM available is generally far less than in a stand-alone set-up. Device drivers for the network portion of the system consume valuable RAM, sometimes to the point where the software will not operate. Table 1 illustrates how available RAM can quickly shrink from the installed 640 kilobytes.
Table 1 illustrates only one example. Other network software configurations, for instance, will have different memory requirements than the IBM software started in the redirector mode. …