Magneto optical disk (MO)



Hi guys,

I need help doing a report regarding magneto optical disk. I hope there’s a expert that know alot about MO. Basically, what i know is magneto optical disk is NOT DVD-RW, CD-RW. It is totally a different thing.

May i know what charactertistic can we compare between two similar disk produce from different company ( sony , verbatim etc)

Thanks for your help.


Anyone used MO before?


Yes, I bought one of those 21 MB Floptical drives that Iomega sold back in the late '80’s early '90’s. It was supposed to be a replacement for a 3.5" floppy drive in that it would allow you to read/write to normal floppies as well as the 3.5", 21MB floptical discs. There were other MO discs available that were similar in size and appearance to CD’s, except that they were encased in a shell, similar to what you had to put CD’s in for the early 3x+ CDROM drives. I could not afford one of those higher capacity MO’s. I had horrible luck with the Iomega 21MB drives. The disks crapped out after only a few writings. I lost data and the disks became useless. And, as far as I know, only Omega made the 21MB disks so I can’t compare their quality against another’s. All in all, I should have taken the money that I spent on the disks and the drive and just bought more floppies, I’d have had less trouble and lost less data. The higher end MO drives were probably more reliable and not as trouble prone, so hopefully someone can provide you with better info. than I can.

Edit: One thing I can say, though, is that the floptical drives were as easy to write to and erase as a normal floppy, although I believe there was a bit more of a hoop to go through when formatting them that you did not have with the floppies, than are the current R and RW CD’s/DVD’s (i.e. you did not have to burn all files at once or create sessions). Yes, with RW disks you can use packet writing software and get the same ease of writing/erasing, however, and perhaps this is a weakness in all optical media (now that I think of it, including semi-optical like the MO disks) since I have lost a lot of data using packet writing software.


at work we have mo 230 drive (230Mb a disk) on a p1 computer running unix and pcs(siemens/texas graphical interface, for marmalade processing) It’s a pain in the B** for backing up. damn slow. I think it could be best compaired with today’s dvd-RAM the disks look simular only smaller and in a casing


Magneto-Optical disks use the following technology:

When a ferromagnetic material is heated, it loses the magnetic properties. However, when it’s heated and cooling, it’s possible to direct the magnetic field of it in either direction. The MO drive heats up the magnetic surface using a laser, to write or read data [different current based on field direction]

Essentially this means: when you read data, the data is destroyed and has to be rewritten, so you read then write. When you write data, you write.

The laser itself is not used for tracking [like on a cd], just for heating up the surface. Essentially, it’s like a hard drive, only the magnetic heads are replaced by a laser.



I believe you are mistaken. MO media use lasers to write data to the discs and magnetic heads to read data from the discs. Some of the discs, I remember, were WORM discs (i.e. write once read many, like CDR’s) others were re-writable like CDRW’s. Therefore, you can’t have the drive destroy the data as it is read as the WORM media could not be erased or re-written to, just like CDR’s.

As far as how the laser interacts with the magnetic material on the disc, you may be correct as I was never clear on what exactly the laser did to the material to write the data to it.


My advisor was the person who helped develop this while working at IBM, he recieved a national technology award (from the president), anyway his name is Richard Gambino. I did my MS thesis under him at Stony Brook University. Saruman and ASk are pretty much on the money. The heating of the laser changes the material between an amophous and crystalline phase.


If i remember correctly, MiniDisc’s are/were MagnetoOptical discs. Someone may correct me on this, but 1 thing is for sure, I put a magnet near one by mistake and it no longer works lol


That’s why. It uses a magnet to record and a laser to read.


I been told that MD’s are CD-RW phase change based not MO. Magnet does nothing to my MD :slight_smile:


Inconclusive, in regard to the MD being an MO. A magnet should not change an MO disc. The magnetic properties are changed through heat or radiation via the laser (the writing head). The reading of the disc is performed by the typical magnetic pickup head. Simply running a magnet over the media should not erase or mess up the data in anyway. Of course that’s in theory, reality may mean that you can mess it up with a very strong magnetic field or cause some minor problems with a weaker one, but I find that unlikely.


[I]In 1992 the MiniDisc system was introduced in the consumer audio market as a new digital audio playback and recording system (Fig. 1). The introduction time was just ten years after the introduction of the Compact Disc (CD). As is known, CD has effectively replaced the vinyl LP records in the audio disc market. CD technology is based on 16-bit quantization and 44.1-kHz sampled digital audio recording. The CD sound quality was fairly improved compared to any consumer analog recording equipment.

Before starting the CD business, many engineers engaged in the development of the CD solely for its improvement in sound quality, but after the introduction of the CD player into the market, we found out that the consumer became aware of the quick random-access characteristic of the optical disc system. In addition, the size of the 12-cm disc was easy to handle compared to that of the LP. The longer lifetime for both the media and the player strongly supported the acceptance of the CD format. The next target of development was obviously to be the rewritable CD. SONY and Philips jointly developed this system and made it a technical reality in 1989. Two different recordable CD systems were established. One is the write-once CD named CD-R and the other is the re-writable CD named CD-MO.

Sales of cassette tapes had been decreasing since 1989, and Sony felt that the compact cassette system was approaching the end of its format life. Even if recordable CD were to be accepted by the consumer, it would still be difficult to break into the portable market. Here, portable compact cassette dominated because of its strong resistance to vibration and its compactness. Clear targets for a new disc system were to overcome these weaknesses. Sony was able to achieve this by introducing a disc system called MiniDisc (MD).

Magneto-optical disc recording technology has been used for computer data storage system for several years. Based on this technology, we had developed direct overwriting technology with a similar recording density as Compact Disc. Additionally, we employed a shock-resistant memory control for portable use and applied a digital audio compression system called ATRAC (Adaptive TRansform Acoustic Coding) that enabled us to use a 64-mm disc size. Recent technological improvement of semiconductors helped to realize this technology. [/I]


I was just reading about MO from some old computer magazines from the early 90s.

The laser heated up the sectors. At the higher temperature (Curie point, I believe), the magnetic properties could be altered by a magnetic head. So the magnetic properties could only be changed at the high temperature provided by the laser. Apparently, two passes were required to write to the discs.

Anyway, this means the laser didn’t actually do the writing. The laser heated up the material so that magnetic heads could do the writing. Then, they would be read back by the laser. The bits were represented by two different polarities of light which could be read back optically.