Ultrahigh-Density Recording Technologies
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erasable versions of these drives are expected in the future. These new DVD technologies are expected to enjoy larger markets than previous optical-recording technologies, but they are not expected to impact upon the hard-disk-drive business. They are likely to compete for some of the same markets as tape drives and flexible disk drives, but it is likely that all of these technologies will continue to enjoy significant markets for at least the next 5-10 years. New technologies are also being developed to fulfill new needs. Holographic optical storage offers short access times and high transfer rates of large quantities of information. Products are still far from being defined, but it appears that holographic storage, if successful, will be used for data storage on large high-performance computer systems, at least when initially introduced. The key need in holographic data storage is a sufficiently reliable, erasable, and defect-free material. This issue of MRS Bulletin focuses on the materials advances that have occurred and that are expected to make future advances in data-storage technology possible. Because of space limitations, not all possible storage technologies will be covered, but the major currently used technologies, and some of the most promising new technologies are. Materials for magnetic-recording heads, magnetic disk and tape media, erasable optical media (both phase change and magneto-optic), and holographic data storage are addressed by experts in each of these areas. The following are brief explanations of the features of each technology and highlights of the issues that need to be addressed for the continuing advancement of the technology.
Magnetic Hard-Disk Recording Magnetic hard-disk drives enjoy by far the largest market of all the various stor-
age technologies with over $25 billion in sales.1 The number of drives sold is currently increasing at a rate of about 20% per year. However due to reductions in prices, the overall market revenue has recently been flat. Revenue is projected to grow and approach $70 billion in 2005.2 The original hard-disk drive, which was known as the RAMAC and was built by IBM in 1956, had an areal density of 2,000 bits/in. 2 , a data rate of 70 kbits/s, and used 50 24-in. disks to store five Mbytes of information. It was considerably larger than a refrigerator and though most were leased, the cost was of the order of $100,000 ($20/Mbyte). By comparison the most recent disk drive announced by IBM has an areal density of 1.3 Gbits/in.2, a data rate of 75 Mbits/s, and uses three 2.5-inch disks to store 2.2 Gbytes of information. As phenomenal as this long record of progress has been, the rate of progress today is higher than it has ever been in the past. From 1956 to 1991, the rate of progress in areal density was about 23% per year (or 10 times every 10 years). However since 1991, the areal density has been increasing at the rate of 60% per year (or 10 times every five years). Over this 40-year time period, there have been a large number of innovations made in the t
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