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Optical storage
A new combination of materials and lasers revolutionized data access and retrieval
Computer storage has come a long way from punched cards made of thin cardboard. Magnetic tape and disk drives took hold in the late 1950s, followed by floppy disks and memory sticks in the ensuing decades, with each new medium offering some combination of higher capacity, lower cost and greater portability. Few areas of technology have seen such rapid declines in cost and size along with equally dramatic improvements in capacity and performance.
Optical data storage emerged in the 1990s, utilizing lasers to write to, and read from, small disks that contain a light-sensitive layer to store information. When it comes to storing data, optical media offer several advantages over magnetic media.
Optical disks deliver a lower cost per bit and have greater storage capacity. They also provide very high stability. Unlike magnetic disks or tape, optical disks aren’t vulnerable to electromagnetic fields, and they don’t wear out easily with continuous use.
The magneto-optical disk
Early versions of optical disks were created by researchers in the 1960s, and optical disk technologies appeared on the market in the early 1980s in the form of CDs and DVDs. At first these were used mainly for music and movies. CD-ROMs were read-only, and not a writable medium. Standard CDs could hold about 700 megabytes of data, enough for 80 minutes of music or about 500 photos. But the ever-growing amount of computer-generated data created the need for a new form of high-capacity removable storage.
That led to the invention of the rewritable magneto-optical (MO) disk, pioneered by IBM. Housed in cartridges, MO disks are a combination of magnetic and optical storage and can be rewritten up to 1 million times. MO disks use lasers that heat the bits on the disk, after which a magnet changes the bit’s polarity according to what’s being written, thereby storing the information. MO disks are extremely durable and offer very reliable, high-capacity data storage.
The MO disk emerged from the work of three IBM researchers, Praveen Chaudhari, Jerome J. Cuomo and Richard J. Gambino. They were working at IBM’s Thomas J. Watson Research Center in Yorktown Heights, New York, in the 1970s when they discovered a combination of elements that possessed unusual magnetic and optical properties that made them an ideal medium for data storage. The elements could be easily and repeatedly magnetized to accept large volumes of data at very high speeds.
The MO disk team
Trial and error
It took the three IBM researchers almost a decade of trial and error to hit upon the precise combination of materials for the MO disk. Gambino, who worked in magnetics, suggested combining the rare earth element gadolinium with cobalt. The researchers had learned, through advice from an older colleague, the necessity of working with pure samples of such materials. This would prove critical.
Gambino believed that the molecular structures, or lattices, of the two elements would complement each other, allowing magnetic domains to “stand upright,” or perpendicular — a necessity for high-density magnetic recording. Cuomo used a technique called sputtering to place the elements on a substrate. This involved bombarding the metals with energized particles to release atoms, which were then set down on the substrate. He prepared film deposits on a variety of substrates, including molybdenum, a silvery-gray metal that can withstand extreme temperatures without significantly expanding, making it useful in environments of intense heat.
At one point in this long process, the films that were deposited became contaminated by the molybdenum holder. Tests showed that this new, three-component alloy had the superior properties they were looking for, including heat resistance. “This new alloy made the technology attractive and competitive,” Cuomo said.
Optical storage hits the market
After numerous trips to IBM facilities around the world, Cuomo and his colleagues found that engineers at the IBM Tucson Development Laboratory in Arizona had a keen interest in their discovery. In 1991, IBM became the first company to deliver a 3.5-inch rewritable optical drive to the market. Within two years, the company expanded its product line to include 5.25-inch drive products and optical library storage systems, such as the IBM 3995 Optical Library Dataserver. This machine held an array of optical cartridges, each initially capable of storing 680 megabytes of data, and eventually eight times that amount, or 5.2 gigabytes.
The three IBM researchers were awarded the National Medal of Technology, the US’s highest honor for technical innovation. By the mid-1990s, their work had become the foundation of a USD 2 billion rewritable-optical-disk data storage industry.
In recent years, optical disks have gradually lost popularity since large volumes of data can inexpensively be stored in the cloud. But the durability and high storage capacity of optical disks ensure they will continue to be used for years to come to create archives of important information for business and government. Today’s optical disks can store terabytes of data and offer up to 100 years of reliable data retrieval — a formidable combination of capacity and durability.
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