July 90 - CD-ROM: THE CUTTING EDGE
CD-ROM: THE CUTTING EDGE
MARK B. JOHNSON
Just as applications changed when hard disks became widely available, they are
beginning to change again to take advantage of the newest storage technology to go
mainstream: CD-ROM. The acronym, which stands for Compact Disc--Read Only
Memory, doesn't begin to tell how the technology can liberate your applications from
the currently established limitations of magnetic media. This article discusses the ups
and downs of CD-ROM and looks at simple and creative ways developers can take
advantage of this new medium.
With its advantages over traditional magnetic media, CD-ROM can help you establish a
real difference between your products and those of your competitors. It can enable you
to produce ground-breaking applications at an affordable cost, unconstrained by disk
space limitations. Although it does have its own limitations, its advantages and the
possibilities they offer should be enough to convince you to make the investment in
this competitive weapon.
THE CD-ROM EDGE
CD-ROM puts traditional magnetic media to shame in more ways than one. Beyond the
obvious advantages of high capacity and low cost, no magnetic media can match CD-ROM
in the areas of versatility, durability, portability, and interchangeability.
Capacity. Optical encoding of digital data enables storage of up to 660 MB of
information on a single 120-mm CD-ROM disc. It would take more than 800 floppy
disks to hold the same amount of information. Although some recording techniques
limit CD-ROM discs to 550 MB, even a disc with this lower limit holds more
information than hundreds of floppy disks.
Economy. You would think that with its capacity and durability, CD-ROM would be
quite expensive. On the contrary, when you need to distribute at least 10 MB of data to
100 or more people, CD- ROM is a very cost-effective medium. Large numbers of
discs (over 1,000 units) can be produced for near two dollars per disc, almost as low
a cost as for producing a standard 800K floppy disk.
Versatility. A CD-ROM disc can contain both digital data and high-quality digital
audio tracks (usually copied directly from a digital audio tape). Thus, this technology
opens the door to newcombinations of data and sound on a single medium. See Eric
Mueller's article "Accessing CD- ROM Audio Tracks From Your Application" in this
issue for insight into how such things are done.
Durability. Because CD-ROM is a read-only medium, a disc has a high degree of data
integrity once it is pressed. Users cannot erase or overwrite the data, nor can they
accidentally infect the disc with the latest virus. CD-ROM discs are mostly comprised
of, and completely coated by, durable plastic. This construction, combined with the fact
that the data encoding method used today provides its own error correction, makes
CD-ROM a highly stable and durable medium, resistant to the handling and magnetic
damage that commonly affect other types of media. (To prove this point a few years
ago, an Apple engineer buried some CD-ROM discs in his cat's litter box for a week. He
then wiped the discs clean and successfully read all the data from them.)
Portability. Another advantage of optical technology is its portability. Unlike most
sealed hard disk platters, CD-ROM discs can be removed from a CD-ROM drive. This
feature gives the user a virtually unlimited amount of storage space without locking
him or her into a single type of information from minute to minute.
Interchangeability. Any CD-ROM player can read any CD-ROM disc at the bit level,
since all CD- ROM discs, whether they contain data, audio, or both, share a common
physical format. To go one step farther, developers can use a standard file system
format to enable users to access a disc on a variety of hardware configurations under
several different operating systems. Brian Bechtel's article "The Ins and Outs of ISO
9660 and High Sierra" in this issue explores the two standard file system formats.
Developers can also mix partitions on a disc so that it can be read by both the
Macintosh ® operating system and ProDOS ®, as explained in Llew Roberts's article
"How to Create a Mixed- Partition CD-ROM" in this issue.
SO WHAT'S THE CATCH?
All this for one low price? There must be a catch. Not exactly. Some minor limitations,
yes--in the areas of speed, inability to write on the medium, and cost of a CD-ROM
drive--but no show-stoppers.
Speed. Due to the mass of the optical read head and the data encoding methods used,
reading from a CD-ROM disc is slower than reading from a good hard disk, but still
faster than reading from a floppy. The speed of reading from disc, which is 150K per
second, is sufficient for just about anything but uncompressed, full-motion color
video, but any application that requires a lot of disc access (for example, HyperCard)
suffers some performance degradation if run directly from CD- ROM instead of from a
hard disk. Of course, if you are just using CD-ROM as a means of distributing your
software, then speed really is not a problem since users are most likely going to copy
your software to their hard disks or file servers to use. But even in cases where speed
does matter, there are things you can do to address this concern; see the sidebar
"Maximizing CD-ROM Speed.
Inability to write. The read-only feature that makes CD-ROM so durable is
considered by some to be a disadvantage to this technology. Since you cannot erase or
overwrite CD-ROM, it is not a replacement for magnetic media. Optical technologies
that allow writing as well as reading are coming to the market--including read- only
and erasable-optical discs, laser videodiscs, and WORM (write once, read many)
discs--but none of these can currently match the cost-effectiveness of CD-ROM for
electronic publishing and distribution.
Cost of a drive. Although Apple recently cut the price of the AppleCD SC to be
comparable to that of an average-sized hard disk, many developers still consider the
cost prohibitive for the mainstream user, and therefore do not consider a CD-ROM
drive a mainstream peripheral. It is true that today's installed base of CD-ROM drives
is small, but it is beginning to grow at a faster rate as more and more new titles
appear on the market. Here we have the familiar chicken-or-egg problem: developers
want to wait for the installed base to reach a certain point before they develop for CD-
ROM, and users want to wait for the number of useful CD-ROM products to reach a
certain point before they buy a CD-ROM drive.
Still, the fact is that it may only take a single blockbuster CD-ROM to motivate many
people to buy. For example, when Apple's Developer Technical Support group produced
the original Phil & Dave's Excellent CD (now a collector's item), many developers
found it reason enough to buy a CD-ROM drive. If your product is good enough, people
will purchase the necessary hardware to use it. And remember that competition is
forcing the cost of CD-ROM drives and discs ever downward, so you can bet that by the
time you get your product to market, price will be less of a limiting factor than it is
now.
A WORLD OF POSSIBILITIES
Thanks to its advantages over other technologies and despite its minor limitations,
CD-ROM opens up a world of new possibilities to the developer. CD-ROM is especially
suited to
• distributing large products
• creating new or enhanced versions of products
• distributing application environments
• enabling collaborative products
• distributing information products
• enabling interactive media products
• enabling user interaction in a learning environment
We'll look at some examples of each of these kinds of uses.
As we look at these examples, keep in mind that although building a CD-ROM is
essentially as easy as cloning a hard disk, building in a look and feel that takes full
advantage of the medium is a more challenging task. You must pay attention to simple
things like data organization and window size and position on the disc. If a CD-ROM is
not well organized, your user might as well be dealing with 825 individual floppy
disks. Ideally, you want to present a consistent interface and make it as visually
appealing as possible to the user.
DISTRIBUTING LARGE PRODUCTS
The simplest way to use CD-ROM is as a distribution medium for relatively large and
complex software products. Development system environments and other
comprehensive products like them are perfect candidates for CD-ROM distribution.
With the increased disk space, you can include several different preconfigured
versions that a user need only copy to a hard disk without going through a complicated
installation procedure.
If your product requires a specific version of Apple's system software, you can license
the software from Apple Software Licensing (20525 Mariani Avenue, M/S 38-I,
Cupertino, CA 95014, 408/974- 4667) and include it on the CD-ROM to make sure
your users have everything they need to run your product when they acquire it.For
Apple, products like MPW ®, MacApp® , and System Software 7.0 are great
candidates for CD- ROM distribution, but the real win with CD-ROM technology is to
create products that you may not have even thought possible prior to the availability of
this medium.