Mass Storage

Article excerpt

This section deals with a very basic question: now that the multimedia material has been created, how can it be stored?

Users who need to pay attention to this side of a multimedia system are those who are, or are planning to be, authors. This is a larger universe than it may first appear-- once a person begins to experience multimedia, the next inclination is to get in there and "do it myself."

What if, for example, a university professor needs to give her presentation at a conference in another city? Or what if a full class of students is assigned to create and present a multimedia marketing plan for Ye Olde Widget Company? And what about off-site training? These situations and others require a mass-storage device.

Several options for storing a multimedia application exist. One is a portable hard disk. Small and lightweight, some of these will fit into a shirt pocket; most others slip into your briefcase. And due to the proliferation of notebook computers, to which they are well suited, there is a bloom of choices. However, portable hard disks are really only a viable option if the user is the owner, which is not particularly appropriate to the environment of education.

REMOVABLE MEDIA SYSTEMS

Better suited to educational institutions are products broadly classified as removable media systems or removable Winchester drives. Basically this is a hard disk in a cartridge. Available generally in 44MB or 88MB capacities, a special 5.25" magnetic hard disk is encased in a plastic shell to form a cartridge, which is then inserted into a special drive. Access times hover around the 20 millisecond range, similar to a traditional hard disk's time.

Such devices are particularly well suited for multimedia storage and presentation. It's like having an unlimited number of hard disks. Every student can have their own. Researchers can separate data by project, utilizing only that cartridge holding the pertinent information. And multimedia presentations can be built and then stored on a single cartridge. For a school or university, equipping a workstation with one of these devices enables an unlimited number of users.

Further, some systems offer dual drivesto double the space to more than one gigabyte. Network compatibility is standard. And new technology is boosting both speed and capacity.

REWRITABLE & MULTI-FUNCTION

According to Disk Trend, Inc., the worldwide shipments of optical disc drives with read/write capability for computer applications increased by 91.5% in 1989. Further, it estimates more than 995,000 units will be in use by 1993. These impressive numbers reflect the growing confidence in optical media for data storage.

Of the optical disc drives now available, two types best suit multimedia applications: rewritable and multi-function. Rewritable drives tend to get the most attention; a multi-function drive is known for its economy-of-scale factor.

Rewritable optical drives and their CDs come in two sizes. A 3.5' disc holds 128MB and the 5.25" disc holds between 600MB and 1 GB; half is on each side. The access times, between 30 and 70 ms., are not as quick as hard disks but still fast enough.

In addition, two different technologies go into rewritable drives and each requires different media. Magneto optical (MO) uses a combination of magnetic and laser technology to record data on the disc's surface. A tiny laser applies heat until the polarity of the magnetic field changes; polarity determines if the spot is a one or a zero. In MO, two revolutions are required in the write process: one to erase and one to write.

Phase change, a newer technology, needs only one revolution of the disc to write data. The media itself is originally in a formless state. To write, a laser heats a spot till it reaches a specific temperature and crystallizes. Ones and zeros correlate to crystallized and noncrystallized spots, and no magnetic technology is involved. …