On Friday, I had the opportunity to join the Virginia chapter of the Special Libraries Association on a tour of the Library of Congress Packard Campus for Audio-Visual Conservation. It was a spectacular experience – now I know what 50 petabytes of data storage capacity look like, what a U-matic reformatting robot looks like, and what severely deteriorated nitrate film looks like, among other things.
It put me in mind of this tweet from Hannah Wiatt Davis last month and our ensuing conversation about the many unfamiliar non-print media carriers that newer professionals might encounter in the library.
Many library schools do not cover these types of media carriers outside of an archives or preservation class, but in fact many of these more obscure or outdated media are still floating out there in the stacks. It can be helpful to have an understanding of what these formats are, how they work, and how to handle and use them, even if you are not in charge of preserving, reformatting, or cataloging them.
There are more carrier types out there than you can shake a stick at, and if you’re seriously stumped there are resources you can consult like the National Library of Australia’s Mediapedia, but here is a rough guide to some of the most common terms and carrier types you may come across.
RDA, or Resource Description and Access, breaks down any cataloged item into three components: the content, the media, and the carrier (the 336, 337, and 338 fields, for the MARC-savvy among you), so those are the terms I’ll use here. Content is pretty self-explanatory; it includes terms like text, spoken word, or two-dimensional moving image and tells you how the information is expressed. Media is a little more complicated, since it is a term that has many meanings in the English language. In RDA terms, it lets you know what kind of mediation is needed to extract the information. For example, a book or picture that you can read with the naked eye is unmediated. It also includes terms like audio and video. Carrier is the most important term for this post; it provides information about what the information is on or, if you will, how it is embodied. This can be seen almost as a subfield of media and may contain terms like audiocassette, videodisc, or filmstrip. So when you hear the term “carrier” or “media carrier,” you’re talking about the physical object of information storage, independent of its content or the experience of its content.
It’s also useful to start out with a basic understanding of the difference between analog and digital, terms which describe how the information is transmitted to and from the information carrier. In the most basic terms, an analog signal operates continuously across a spectrum of values, while a digital signal essentially samples a discrete number of possible values. So even though we often use those terms as shorthand for media carrier types (like cassette tapes or vinyl records), they actually refer to the method of transmitting streams of information.
Broadly speaking, magnetic media carriers use some type of magnetizable surface to store information encoded in magnetic signals. Magnetic media equipment (like your trusty tape deck) uses a read/write head to magnetize the storage medium. It is important to be careful with magnetic media, because the information on them can easily be lost by exposure to magnets like the security-strip de-sensitizing magnets commonly used at library circulation desks.
Analog magnetic media
Early broadcast television began to make use first of two-inch and then one-inch magnetic tape reels in the 1950s, 60s, and 70s. Because they were very expensive, were frequently reused by stations and studios, and had little use outside the industry (and, thus, specialized archives), I won’t cover them here. In 1971, Sony first introduced the video cassette for consumer use, the U-matic, which used three-quarter inch tape and pioneered the use of the protective plastic cassette, as opposed to reel-to-reel. Half-inch Betamax and VHS tapes and 8mm Video8/Hi8 tapes were the successors to the U-matic, with increasingly smaller cassettes and longer running times. For audio, the quarter-inch eight-track and eighth-inch compact cassettes were the most popular. The Super VHS (or S-VHS) and Hi8 formats also began enabling digital recording of the audio track with the use of professional-grade recording equipment.
Digital magnetic media
Floppy disks and hard disks are the most common forms of digital magnetic media. While you aren’t likely to find a hard disk in the stacks, you may run across floppy disks, which were manufactured in 8 inch, 5-1/4 inch, and 3-1/2 inch sizes. Like the videocassette, floppy disks first became commercially available in the early 1970s. They consist of a thin, flexible disc of magnetic material encased in protective plastic; the data can be read through small apertures which, on the later 3-1/2″ model, is further protected by a metal slider. The 3-1/2″ floppy disk also has a metal hub in the center (visible from the back) on which the disk rotates, while the earlier 8″ and 5-1/4″ sizes just have a hole in the center.
Optical media store information in the form of pits that have been engraved or stamped on a substrate. Equipment that reads optical media uses a lens to reflect light against the pits. Unfortunately, optical media can easily be scratched, which obliterates information from the surface, and they tend to deteriorate very quickly.
Analog optical media
The primary optical media format using an analog signal that you might still run across is the LaserDisc (also known as a laser videodisc or LaserVision), which was 30cm (11.81 in) in diameter and was composed of two single-sided aluminum discs laminated in plastic. It could be used either for video or for audio recording, and debuted commercially in the late 1970s. They were also often used to store cultural heritage information; in 1979, the Museum of Science and Industry in Chicago used laserdiscs in its interactive exhibit on newspapers, allowing visitors to search for any front page of the Chicago Tribune. The BBC also famously used laserdiscs for its original 1984-86 project celebrating the Domesday Book, which included analog still and moving image content together with digital data storage; a complex process was required in the early 2000s to recapture the information and migrate it to a more accessible format.
Digital optical media
CDs and BluRay are the most common form of digital optical media — hopefully I don’t have to explain what those are (quite yet…)!
So, hackers, let me know in the comments! What other forms of media carriers have you encountered in the stacks? Did you have any classes that covered different types of media, and if so, what did you learn?