We all know DVDs, small digital discs that can hold, for example, an entire movie. But in the 1970s, before the format war between videocassettes, another type of medium was trying to find its market: we’re talking about videodiscs.

Videodiscs

The same size as 33 RPM audio records and entirely analog, these were supposed to flood consumers’ homes along with a sea of content, a modern term that in the field of visuals refers to movies, TV series, and video clips.

Three formats

Today we’ll talk about three generations of videodiscs. Two that emerged in the early 1970s from Bogen GmbH and RCA, very similar to the classic vinyl record. The third, born at the end of the same decade: the splendid LaserDisc, an analog format that at first glance looks like a giant version of the digital DVD.

Videodiscs BOGEN

Let’s start with the one introduced by Bogen GmbH and thoroughly described in an exhaustive article by the late Prof. Marino Mariani, founder of the magazine Audio Visione in 1971. The professor was what today would be called a visionary: in the article, for example, he hoped that video recording, instead of being analog, would in the future be done through encoded pulses (abbreviated as PCM). In short, he was talking about the digital disc a decade in advance.

On standard turntables

But back to the Bogen disc. Designed to be played on a standard turntable (in the cover image, a Dual 701), the system featured a disc that was half vinyl (complete with grooves) and half magnetic.

Magnetic Disc Recording

The recording was magnetic and housed in the outermost part of the disc. The inner half had grooves used solely to guide the tonearm (the stylus, as it was called back then).

Some modifications…

The standard turntable still required some modifications. The simplest: replacing the traditional cartridge with a magnetic one, equipped with a peculiar lateral extension needed to follow the grooves. The more complex: increasing the playback speed from 78 RPM (the speed of records from the 1930s) to 156 RPM.

…and some calculations

Calculator in hand, at 156 RPM, the disc had an average peripheral speed of 2.04 meters per second: for comparison, the musicassette we all know operates at 0.047 meters per second—about 50 times slower. This allowed for a duration of a whopping 12 minutes per side.

Four discs for a movie

Still with our calculator, we can easily deduce that a (short) movie would require four discs, and since these were recorded on both sides, the head of the household (or whoever was unlucky enough to have to flip the disc) would need to get up from the couch an average of eight times for a standard 90-minute feature film.

RCA Videodiscs

No surprise, then, at the lack of success for the Bogen system. This brings us to the one developed by RCA, officially named Capacitance Electronic Disc (CED) but commonly called Videodisc. The medium’s development began as early as 1964.

All in vinyl

Unlike the first, the RCA disc was partially vinyl—but not just a simple layer, as in standard 33 RPM records. The need to record video forced RCA to use PVC mixed with carbon to make it conductive.

Protective silicone

To protect the disc and the stylus, a thin (50 nm) layer of silicone mixed with a special lubricant was applied.

Reading system

The reading system was still more similar to the Bogen system described above than to that of a standard LP. This was inevitable, considering that even a poor television signal requires a signal density about 100 times higher than audio (twenty thousand hertz for audio, two million hertz for video in the RCA style).

Protected disc

To prevent scratches or dust, the disc was always housed in a sleeve that also served as a cover.

Duration

The duration was almost reasonable: sixty minutes per side, so most movies required only one disc. And indeed, the system managed to sell decently, with about 100,000 players sold in the early years of commercialization (1981, after nearly two decades of development).

Short films

As mentioned, 120 minutes was sufficient for most movies—but not all.

And long films

In dedicated forums, you can find accounts from enthusiasts showing how, to fit feature films longer than 120 minutes, the major studios often arbitrarily cut scenes and, in one case, even sped up some secondary scenes.

The disc gets stuck

Despite the protection, dust still managed to creep into the grooves. The result was similar to the classic record that gets stuck.

Endlessly

The difference being that, instead of hearing the same segment of music repeated endlessly, you got an original effect of a broken image while the actors kept repeating the same action.

A good shake

With a method similar to that perfected by players of Pinball, a good shake would resolve the situation.

Early demise

The late commercialization of the RCA disc (as we’ve seen, nearly two decades after the planned date) caused its early demise: a system offering the same quality as videocassettes but without the ability to record was, at that point, doomed to fail in the market. As it did, toward the end of the 1980s.

Laser Videodiscs

We close with the splendid LaserDisc. To convey its size, we photographed it next to a standard DVD. It’s an optical disc, where reading is done not with magnetic heads but with a laser beam. The size (30 cm) is the same as a 33 RPM vinyl, but with a hole in the center as large as that of a 45 RPM record.

Golden disc

The disc, introduced to the market in 1978 by Philips, MCA, and Pioneer, was almost always sold in a golden version. The particular type of engraving caused the disc’s reflections to take on rainbow colors.

Duration

Both sides were usable, but explaining the system’s maximum duration to consumers wasn’t easy. It was first necessary to make the unfortunate user understand that any rotating disc (not just videodiscs) is characterized by two speeds: angular and peripheral. And that, therefore, there are two different types of discs.

Fixed angular speed

Angular speed is the rotation speed: as we know, 33 or 45 are the main angular speeds for audio discs. In the case of the LaserDisc with fixed angular speed (CAV), we’re talking about 1500 RPM.

Forty-five periodic

Back to our calculator: dividing 1500 by 33 gives us 45.45 recurring. A numerical magic trick—the disc spins about 45.454545… times faster than a 33 RPM record.

30 minutes per side

In the CAV system, the duration is 30 minutes per side, like the RCA system: here, the unfortunate head of the household had to get up from the couch an average of four times per movie.

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Linear speed

We’ve talked about angular speed. The second is called peripheral speed: it’s the speed “seen” by the reading head. It obviously varies depending on the distance from the disc’s center—the farther out, the faster it goes.

CLV

The second type of disc, instead of being called “variable angular speed,” was dubbed “fixed linear speed”: perhaps a way to make the concept sound more elite.

Comparisons

But that’s not enough to scare the readers of 70-80.it. So here’s the formula to calculate the linear speed at the edge of our disc:

In other words, the scrolling speed is 4.71 meters per second, twice that of the Bogen disc we started with (and a hundred times faster than a musicassette).

Extended duration

By keeping this speed constant (and thus varying the disc’s rotation speed), you get a duration of a whopping 64 minutes per side: our good head of the household will finally have to get up only once, right between the first and second halves. (M.H.B. for 70-80.it)