The technology is far from easy to grasp, but a magneto-optical disk drive works by using a laser to melt the bit-recording spots on the platter with a high-intensity laser in a magnetic field, and differentiating between a zero and a one by switching the polarity of the field. At which point, we seem no forwarder, but the secret is that the phase of the light reflected by the spot varies according to the polarity of the field in which it was melted, and the variations in phase are read by a low-power laser. The problem is that the erase-write cycle is slow compared with that for a magnetic disk, but Sony Corp reckons it has substantially narrowed the gap with a new technique it calls Light Intensity Modulation Direct Overwrite, and has launched two 2.6Gb drives using the technique, which is claimed to double write speeds of previous generation drives, and appears to involve melting out old data and writing new data in one pass where earlier drives require the spots to be erased and returned to a no-data state before they can be re-written. The transfer rate can be as high as 4.0M-bytes per second, and the average seek time is 25mS, which compares with 60mS to 70mS access time for earlier drives. Sony has designed its own platters for use with the drives at $130 to $150 each. Samples of the SMO-F541-DW and SMOF544-DW direct overwrite drives are currently available and they will ship in volume next month at $2,380 for the internal drive with a 1.0Mb cache, and $2,530 for the internal drive with a 4.0Mb cache.
Content from our partners
