11
"You want to wreck a CD?" Russ said. He was wearing the same T-shirt and jeans as on Jack's last two visits. "Easy. Stick it in a microwave and cook till it's all cracked like an old mirror."
Jack had started the digi-head talk as soon as he'd arrived—before Russ could start bitching about his latest reading assignment. The six-pack of Sam Adams Jack had brought along further distracted him from academic matters.
"But, Russ, the idea is to make it unreadable without the owner knowing it's been tampered with."
"Oh, well, that's a different story." He sipped his beer. "I'm assuming we're dealing with a CD-R here and that's a good thing, because they're more easily ruined than the commercial kind."
"I thought a CD was a CD."
"In a way, yes. They both use a laser beam to read ones and zeroes from the disk, but—"
"What about music?"
"Same thing: ones and zeroes. Binary code, my friend."
'Wait a minute. You mean when I'm listening to, say, Jack Bruce doing his bass runs on 'Crossroads,' it's just a series of ones and zeroes?"
"Exactly. The music was translated into binary code that's inscribed on the disk, and the player translates it back."
Jack shook his head in wonder. "I always thought…"
And then he realized he hadn't really thought about it. He put the CD in the slot and hit play. He hadn't needed to know anything more. Until now.
"Let me give you a quick course in CDs and CD-Rs. They both have a single, uninterrupted spiral track, half a micron wide, running from the inside toward the periphery."
"The opposite of a vinyl record."
"Exactly. On a full CD, that track is three-and-a-half miles long. A commercial CD codes its ones and zeroes with bumps and lands: The bumps are ones and the lands—the flat parts—make up the zeroes. The laser reflects off the bumps onto an optical reader that sends them straight to your computer if they're data or to a digital-analog converter if music. All this at 450 rpms."
"Yow. Complicated."
"The tracking makes it even more complicated, but we won't go there."
"Thank you."
Russ smiled. "That's the commercial CD. The homemade CD-Rs use a slightly different technology. Instead of bumps and lands, they take a stronger laser and heat up a series of spots on a dye layer in the plastic. The heat changes the spots' reflectivity, creating virtual bumps."
"So where does that leave me?"
"Well, since you don't want anyone the wiser, that leaves out scratching or marking with a pen or dipping in acid. So I can see only two options. The first is to take some sort of X-Acto knife and use it to enlarge the central spindle hole—just a little. Won't take much. Just a small change in the diameter will cause a wobble in the disk as it's doing its 450 rpms, and that wobble will cause the tracking system to mess up, which will mean the laser's reading bumps and lands off multiple tracks—they're only a micron and a half apart—which will completely confuse the optical reader. The result will make Jabberwocky read like Dick and Jane"
He made a dramatic flourish with his free hand while he drained his beer bottle.
"But the data's still there, right?" Jack said. "So if someone could fix the spindle hole, they could get their data back."
"Tjfthey knew the hole had been tampered with, and if'they could make a perfect restoration. Both highly—highly—unlikely."
"But not impossible."
Russ sighed. "No, not impossible."
"What's the other option?"
"Bring along a hot plate and heat up the disk just enough to give it the slightest warp. A sixteenth of an inch, even less, will do it. The laser beam will reflect all over the place, hitting the optical pickup only by chance."
"But what about—?"
"Fixing the warp? Never happen."
He popped the top from another Sam and offered it to Jack who waved it off.
"You're sure?"
Russ gave a vigorous nod. "Once warped, that plastic will never be perfectly flat again, the tracks in the dye layer will never line up just right again."
Jack liked it. Just his thing: simple and low tech.
"You wouldn't happen to have a hot plate sitting around, would you?"