Microdrive

GMR technology was a key feature of IBM's (the company's hard disk drive business was subsequently acquired by Hitachi Global Storage Technologies in 2002) revolutionary Microdrive device, launched in mid-1999. The world’s smallest, lightest one-inch Harddrive was invented at IBM’s San Jose Research Center by a team of engineers engaged in the study of micromechanical applications such as Si micro-machined motors and actuators for possible usage in very small disk drives.

The Microdrive uses a single one-inch diameter glass platter with a metal coating which is less than a thousandth of the thickness of a human hair. Powered by nine elecromagnets, the spindle motor spins the 16g disk at 4,500rpm, data being transmitted and received through the actuator's miscroscopic read-write heads as it sweeps across the disk. Rubber shock absorbers and an actuator locking latch prevent damage to the disk's surface, both under normal operating conditions and if the unit is jarred or dropped. The drive's circuit board acts as the drive's brain, controlling its functions from speed to dataflow.

The tiny elements inside the Microdrive confer some unique advantages. For example, since the actuator has 50 times less inertia than one in a larger drive, it can ramp up to speed in half a second. Consequently, its possible to allow the drive to stop spinning when data is not being accessed - thereby improving the device's power conservation characteristics.

The tiny elements inside the Microdrive confer some unique advantages. For example, since the actuator has 50 times less inertia than one in a larger drive, it can ramp up to speed in half a second. Consequently, its possible to allow the drive to stop spinning when data is not being accessed - thereby improving the device's power conservation characteristics.

Use of the industry-standard CF+ Type II interface - allowing easy integration into a variety of handheld products and providing compatibility with PCMCIA Type II interface via the use of an adapter - took CompactFlash storage into completely new territory, enabling high-capacity yet cost-effective personal storage for a wide variety of electronic devices.

The Microdrive was initially released with capacities of 170MB and 340MB, with a claimed seek time of 15ms, average latency of 6.7ms and a data transfer rate of between 32 Mbit/s and 49 Mbit/s. In 2000, 512MB and 1GB versions were released and capacities continued to boost, reaching 8GB by 2005. By that time, other manufacturers had entered the market, with Seagate having launched an 8GB 1in drive in the same year and Sony licensing re-badged Hitachi-made models under the brand name "Sony Microdrive".

Hitachi expects to see the recent advancements in Perpendicular Magnetic Recording (PMR) technology translate into storage capacities of up to 20GB on a one-inch Microdrive by the year 2007.

OAW technology

While GMR technology is looking to areal densities of up to 40Gbit/in2 in the next few years, some hard disk manufacturers anticipate that the phenomenon of losing data due to data bits being packed too close together will begin to happen when drives begin holding around 20Gbit/in2. The Seagate subsidiary, Quinta Corporation, is planning to combat this storage technology barrier, otherwise known as the Superparamagnetic Limit, with its Optically Assisted Winchester (OAW) technology, expected to appear sometime during 1999.

OAW has as much in common with magneto-optical technology as conventional magnetic hard drives, but uses a clever bundle of techniques to get around the size and Efficiency drawbacks of MO formats. The technique uses laser light to select various heads within the drive, rather than the typical electromagnetic system in conventional drives. The principle is simple: a laser is focused on the surface of a platter and can be used for reading and writer. The former relies on the Kerr Effect, whereby polarised light bounced off a magnetised surface has its polarisation twisted. Put that through a further polarising filter and the intensity of the light corresponds to the alignment of the illuminated domain.

This method of reading needs less power from the laser, so the heating effect on the medium is minimal, preventing data corruption. The same laser and optics can be used for writing, using a magneto-optical technique. A tiny spot on the hard disk is heated with a higher-power output laser to beyond the temperature called the Curie Point, above which the surface material's magnetic properties can be flipped with a magnetic coil. This changes the light polarisation characteristics. Unlike regular magneto-optics, however, OAW heats the media and writes to it in one pass, rather than heating on one rotation and writer on the next. OAW is able to do this as it uses a micromachined servo mirror and a minute objective lens to focus the laser very accurately on the smallest area possible. Adjacent areas aren't heated up and are therefore left unchanged.

Since the laser used to heat the media can be focused on a much smaller area than a magnet, higher data densities are possible. The media itself is made of an amorphous alloy that does not have a granular structure, with an atomic level density constraint. Unlike conventional magneto-optical disks, the laser light is carried to the head via an optical fibre rather than being directed via mirrors through air. As a result, the head and arm take up much less space, allowing multiple platter configurations to be fitted into the same example factor as a Winchester hard disk. Efficiency should be comparable to a regular hard disk too, but durability will be much higher, as the disk media is extremely non-volatile at room temperature.