What was the purposes of the Write Protect tabs on CD Caddies?

[NeXT]

If you have a CD caddy near you, grab it and flip it over. On either side near the back there's one-time plastic knock out tabs for an A side and a B side.

What was the purpose? I've been seeing these on caddies for almost 20 years and I have never found a reason why they exist.

-CD Caddy enclosures share nothing with *any* magneto optical cartridge design ever made.
-CD Caddies do not have a B side. You can't flip them over.
-CD Caddy burners did exist, but I've never seen one that took advantage of a write protect tab, given how CD-R's are technically WORM anyways and the disc is removable so why bother?
-They remained part of the injection moulding for the lifetime of the CD Caddy. Multiple manufacturers included them. I have never seen a CD Caddy that did not have them.

 

[kc8eyt]

Perhaps a specification in their original design for future use? Maybe to write protect CDRW media, although not sure if that was even thought of when caddies were specified and designed.

 

[SomeGuy]

Might be jumping to a bit of a conclusion that it must be for write protect. Just some wild guesses

It almost looks like they could be meant for some optional drive supports or latches. That is, one might remove those to use the caddy with some specific non-standard drive model? (But then, why the letters?)

Perhaps the caddie can be attached to something or something else attached to the caddie?

I would sort of assume that unused "holes" on something like this would be partially filled in order to keep dust out.

If you have a drive that takes caddies, does it have any sensors there? (Of course, a lack of such might not tell us anything)

A long, long time ago I used a Windows 3.1 CD-ROM burner that did use a caddie, but I never noticed that detail.

 

[Chuck(G)]

Grabbing a couple of WORM and MO carts, they look just like the above, but with slider tabs for read-only protection. I wonder if there were optical drives that could take either CDs in caddies or regular WORM/MO media. I'd have to dig through a bunch of old literature, but you could do that just as well.

 

[Unknown_K]

The original commercial CDR drives use caddies, so write protect (so you don't finalize a half used expensive disk) would be needed.

 

[Timo W.]

-CD Caddy enclosures share nothing with *any* magneto optical cartridge design ever made.
-CD Caddies do not have a B side. You can't flip them over.
-CD Caddy burners did exist, but I've never seen one that took advantage of a write protect tab, given how CD-R's are technically WORM anyways and the disc is removable so why bother?
-They remained part of the injection moulding for the lifetime of the CD Caddy. Multiple manufacturers included them. I have never seen a CD Caddy that did not have them.

These caddys followed a standard, so they are all the same. Your mistake is to think these were only and solely designed to put in a Compact Disc - but they were not. They were designed with all kind of features in mind.

 

[jafir]

So my first hands on experience with CD-ROM and caddies was in a genealogy library. They had a DOS based computer system with dozens CDs of census and other records. Eventually they added more computers and at one point I remember 3 or 4 workstations with their own CD collection.

I recall most of the drives used standard caddies, like these shown. But there was one computer with a drive that had caddies that couldn’t be used with the other computers’ drives. The little metal sliding door on a normal caddy is one piece and slides both directions. These strange caddies had a split door that opened in the middle. Does anyone recall this kind of drive and caddy?

 

[krebizfan]

The two CD caddy standards I know of were the unified Japanese design which is the most common and the one implemented by Laser Magnetic Storage (itself a joint venture of Control Data and Phillips).

I haven't found any patent showcasing the various additional markings for a CD cartridge and the early cartridge patents lacks it. https://patents.google.com/patent/US4746013A/en is the Sony 1987 CD caddy patent.

 

[Al Kossow]

Caddy for Laser Magnetic Storage / Philips CM201 drive
sold by HP and DEC (as the RRD40)

 

[NeXT]

Maybe to write protect CDRW media, although not sure if that was even thought of when caddies were specified and designed.

Might be jumping to a bit of a conclusion that it must be for write protect. Just some wild guesses

The original commercial CDR drives use caddies, so write protect (so you don't finalize a half used expensive disk) would be needed.

I makes absolutely zero sense why you would put a write protect tab on a caddy which the writable disc is not permanently housed in. Even then, no CD burning software that old would write to a disc without warning.

If you have a drive that takes caddies, does it have any sensors there? (Of course, a lack of such might not tell us anything)

Two drives I quickly opened had metal cone dimples that when a caddy was inserted served to align the caddy in the carriage using the circular holes immediately behind the tabs, but there is no provisions for switches beneath the tab points.

Grabbing a couple of WORM and MO carts, they look just like the above, but with slider tabs for read-only protection.

I can also assure you that 5.25" MO cartridges are physically thicker than a CD caddy, plus the write protect and media type detect switches are different.

Your mistake is to think these were only and solely designed to put in a Compact Disc - but they were not. They were designed with all kind of features in mind.

As Al has pointed out there is indeed other types of CD caddy's that existed and they are physically incompatible with the typical CD Caddy drives and I ahve never seen a CD Caddy being used for other purposes besides CD-ROM drives. The CDTV pushes it as it's more a glorified CD player but on the inside it's still a CD-ROM drive. From a coffee table book I have on a 90's model Porsche another example is the CD Cartridge which again is similar to a CD caddy but not compatible.