If you write too hard on a writeable CD you damage the data. This is because it’s directly underneath the ‘top’ of the CD.
A CD is quite thick, so why not put the data area in the middle of the plastic, where it would be most well protected?
I’ve never trusted writeables since I found this out.
The deeper the data is the higher the laser power needs to be to read the data.
Just to clarify, when I say ‘write’ I mean with a pen or marker.
Right, but surely the amount of power we’re talking about here is negligable. A handheld laser could probably get through a mile of clear plastic! And computers surely have enough power in them for the data to be in the middle.
Oh and I missed the freakin obvious - putting the data in the middle would halve the distance the laser has to travel through plastic. as the data is on the other side of the disc
I expect it comes down to manufacturing costs. With the current configuration, you’ve got a plain old transparent plastic disc, with laminates (chemical, metal, possible reflector layer, printed layer, possible protective layer) added on top. To stick the recordable bit inside plastic you’d have to have two plastic bits bonded together in a way which doesn’t compromise the integrity of the recording layer. Sure it can be done (that’s how DVD-Rs are made), but it is a more complex and hence more costly process. If you buy good-quality media there is already adequate protection (probably some sort of lacquer) added on top, and as long as you use a CD-safe writing instrument it’s all good. Personally, I swear by Sharpie ultra fine points, but YMMV.
The data is in the middle of the disc on DVDs - or more properly, it’s on the inner faces of two glued-together .6 mm substrates.
The optics in CD players are set to work properly when the laser travels through and reflects back from a 1.2 mm substrate.
Since CDs and the players necessary to play them were already in place, CDRs had to conform to the standard Philips Red/Yellow book specification already long in place. CDRs had to play in standard CD players, otherwise it would be a new format and everyone would need a new type of player.
CD started as pre-recorded discs - 1.2 mm in thickness. The discs were printed with screen printers (going even further back - with pad printers). This was long before CD-R was available. On pre-recorded discs, there was no need for the protective lacquer layer (that covers the data layer) to endure being written on with a pen.
This protective lacquer is spun on wet and cured very quickly with a very high-power UV lamp. Unfortunately, the layer is anywhere between 6 and 12 microns thick (average). Sometimes a bit more and sometimes a bit less.
It works great for screen printing (and now offset printing), but it’s real thin.
I don’t know if manufacturers increase the lacquer thickness to guard against pen damage, but considering the tiny profit margin available to manufacturers of CDRs, I would bet that they keep the lacquer as thin as they can get away with.
Practically, some manufacturers of CDRs print areas of the disc to allow easier labeling, but this is also screen printed, and only adds another 8 or so microns of protection between pen and data layer.
When I label discs, I used a fresh fine-point Sharpie, and I don’t bear down too hard.
Fritz thanks for the excellent answer.
I simply don’t label them at all. I only label the case, and identify the cd by the case it’s in, or if it’s without a case I identify it by putting it in a computer.
Having said that, I never burn stuff I really want to keep. I use other methods.