Light Intensity Modulated Direct OverWrite (LIMDOW) technology uses a different write technology which significantly improves on the performance levels of earlier Magneto-optical devices and claims to be a viable alternative to hard disk drives in terms of performance and cost of ownership.
LIMDOW disks and drives work on the same basic principle as a standard Magneto-optical drive: the write surface is heated up and takes on a magnetic force applied from outside. But instead of using a magnetic head in the drive to make the changes, the magnets are built into the disk itself.
The LIMDOW disk has two magnetic layers just behind the reflective writing surface. This write surface is even more clever than Magneto-optical as it can take magnetism from one of those magnetic layers when it has been heated up to one temperature; but if it has been heated up further, it will take its polarity from the other magnetic layer. To write the data onto the disk, the Magneto-optical drive’s laser pulses between two powers.
At high power, the surface heats up more and takes its magnetic ‘charge’ from the north pole magnetic layer. At the lower power, it heats up less and takes its magnetic charge from the south pole layer. Thus, with LIMDOW the Magneto-optical write process is a single-stage affair, bringing write times back up to where they should be - if not competing head on with a hard disk, at least out by only around a factor of two.
LIMDOW became established in the second half of 1997, strengthening Magneto-optical in its traditional market like CAD document imaging and archiving, and moving it into new areas. With search speeds of less than 15 ms and data transfer rates in excess of 4 Mbit/s, LIMDOW Magneto-optical has become a serious option for audio-visual and multimedia applications. The data rates are good enough for storing audio and streaming MPEG-2 video, which brings Magneto-optical back into the equation for video servers in areas such as near-video-on-demand.
Apart from making Magneto-optical competitive on write times, LIMDOW leads the way towards higher-capacity Magneto-optical disks. Because the magnetic surface is right next to the writing surface (rather than somewhere outside the disk itself) the magnetic writing can be done at a much higher resolution - in fact, the resolution of the laser spot doing the heating up. In the future, as the spot goes down in size, with shorter wavelength reddish lasers and then the promised blue laser, the capacity of the disk can jump up to four times the current 2.6 GB or more.
- Scott Mueller, Upgrading and Repairing PCs, Fifteenth Edition, Chapter 12 section «Magneto-Optical Drives» page 670
- White Paper: LIMDOW recording on magneto-optical disk // Computer weekly, Hewlett-Packard, 1999