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Optical Drives: How They Work (Page 1/5)

Posted: May 13, 2000
Written by: Tuan "Solace" Nguyen

Introduction

Last time, we gave you the lowdown on the basics of hard drive mechanics. This time, we’ll be sharing with you how optical storage drives work. I know some of you in the forum had posted messages requesting that I write an article about this type of technology. Well, here we are... Enjoy. We’ll be discussing: CD, CD-R, CD-RW, DVD, DVD-RAM, DVD-RW, MO and LIMDOW (could it be some sort of Microsoft weapon?) technology.

CD

Have you ever picked up a CD and looked at the silver side wondering how on earth information is stored on that plastic disc? Well, wonder no more because we’re going to show you how optical storage devices work.

First off, we’ll start you off with CD (compact disc) history. This technology has been around for almost 20 years (since 1982). That’s right, optical storage technology has been around for quite some time. There is also another technology that has been around for a long time as well -- Magneto Optical (MO) technology (which combines magnetism along with optics).

But the very first we’ll discuss is how CD technology works.

Below is a diagram showing you how the technology works. All optical storage technology is based upon this principle -- except for MO.

On the top side of the disc (the side with print), a thin coat of aluminum alloy is ‘stamped’ onto the polycarbonate disc, and another very thin acrylic protection coat is coated on top of that to protect the medium.

So how exactly does data get put on to CDs? A regular silver-back CD (the ones you buy in stores) isn't recorded using the same method as CD-R discs, but by using specialized presses that stamp the aluminum layer on the disc. It would take forever to have a whole bunch of CD writers sitting there burning away.

This electron microscope scan shows a commercial CD stamped mold which manufacturers inject molten polycarbonate plastic to form the pits and lands.

This electron microscope scan shows a single pit of an audio CD.

This electron microscope scan shows puts that were burnt using CD-R. The pits are rougher around the edges than pits that were stamped commercially.

Data is recorded the same way. A 1 would be a land and a 0 would be a pit.