Second Hard Disk
Winn L. Rosch
Magnetic cartridge drives such as the Jaz and SyJet may be all the rage now, but when magneto-optical (MO) technology first hit its stride in the early 1980s, it showed promise as the removable storage medium of choice for the PC world. Indeed, MO drives still have a long list of advantages, counterbalanced by just one drawback: cost.
We tested three representative MO drives--one at each of the current capacity points--to see where they fit into the removable-storage market.
MO drives use magnetic media with a difference: a high Curie point, which means that for magnetic particles to change polarity in order to store digital bits, the drive must raise the media temperature to about 300 degrees Celsius. To write (or erase) data, an MO drive uses a tightly focused laser beam to heat a tiny spot on the disk. Reading, however, requires only conventional optical technology.
This unique combination affords MO several advantages over other types of storage.
Capacity. MO allows reasonably high-areal densities, hence good capacity. The current 3.5-inch cartridges are rated at 640MB, while 5.25-inch media can store 2.6GB or even 4.6GB per cartridge. This year, 5.2GB drives should become available. (A note on capacity: MO figures are optimistic. A 640MB cartridge has about 599MB of useful storage on a single side after formatting. The 2.6GB and 4.6GB cartridges are double-sided: You have to eject and flip the media to access the full capacity, which after formatting equals roughly 1.1GB or 2.1GB per side.)
Performance. Because the drives use magnetic technology to read data, transfer rates for MO drives rival those of a standard hard disk. Writing takes a little longer than on a hard disk because of the laser technology, but performance is fine for primary or near-line storage.
Durability. Because the bits are written and erased optically, normal magnetic fields don't affect your data. Also, the disks are permanently fixed in rugged cartridge shells that manufacturers have made to demanding shock-tolerance standards. MO vendors rate the useful life of the data stored on the media in excess of 30 years.
Compatibility. Most MO vendors have agreed to keep newer drives backward-compatible within at least two previous generations of MO capacity points. For example, a 3.5-inch 640MB MO drive can accept the older 530MB, 230MB, and 128MB cartridges. Also, most capacity levels follow ISO file-format standards, so cartridges can be exchanged between drives of different manufacturers.
These strengths have given MO a foothold in several key markets such as medical imaging, digital video editing and storage, near-line database storage, and more.
From the April 21, 1998 issue of PC Magazine
Copyright (c) 1998 Ziff-Davis Inc.