Changing of the Discs

How do you fit a CD-ROM reader and four discs into a half-height drive? Alps' 4X uses a four-tray magazine. Once you insert the magazine into the drive, the disc-picking/reading mechanism rises or lowers to the level of the disc you want to play. An arm hooks the appropriate disc tray and pulls it partially out of the magazine stack. Each tray has a large opening on the bottom, providing room for the spindle to clamp it, for the motor to spin it, and for the pickup to read it. The overlapping storage and play areas enable the mechanism to fit within a standard half-height drive.

The NEC MultiSpin 4x4, designed by Nakamichi, tackles the task by eliminating disc caddies, trays, and magazines. The insertion of a bare disc trips an optical sensor that activates a drive belt. The rubber belt contacts the disc at its outermost rim (to avoid damaging data areas) and pulls it into the drive.

The disc stops first at the play position, and the drive's motor, turntable, spindle, and pickup head all rise to clamp, spin, and read the disc. The disc's table of contents is stored in static RAM (SRAM), so the drive knows what's loaded without having to reread each disc every time you power up.

The disc then either continues to play or moves backward to the "stocker," which is a slotted disc-storage area. The elevator-like stocker uses threaded gears to go up and down so that the proper disc can play without being fully ejected from its storage spot. Again, overlapping play and storage areas save space.

Despite their differences, the timings for these two mechanisms are similar. Both drives take about 8 seconds to go from reading one di sc to reading another.

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Nakamichi/NEC Changer

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The Nakamichi/NEC changer mechanism handles bare discs.