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Hard Disk Trends
The most amazing thing about hard disks is that they both change and don't change more
than most other components. In terms of their basic design, today's hard disks aren't a
lot different than the 10 MB clunkers installed in the first IBM PC/XTs in the early
1980s. However, in terms of their capacity, storage, reliability and other
characteristics, hard drives have probably improved more than any other PC component.
Let's take a look at some of the trends in various important hard disk characteristics:
- Areal Density: The areal density of
hard disk platters continues to increase at an amazing rate even exceeding some of the
optimistic predictions of a few years ago. Densities in the lab are now exceeding 35
Gbits/in2, and modern disks are now packing as much as 20 GB of data onto a
single 3.5" platter!
This chart shows the progress of areal density over the
last 43 years. The red line is drawn
as a best-fit through the blue diamonds which are actual products. Key hard disk head
technology developments are indicated. Note that the scale on left is logarithmic, not
Image © IBM Corporation
Image used with permission.
- Capacity: Hard disk capacity continues to not only increase, but
increase at an accelerating rate. From 10 MB in 1981, we are now well over 10 GB
in 2000 and will probably hit 100 GB within a year for consumer drives.
- Spindle Speed: The move to faster and faster spindle speeds continues. Since increasing the spindle speed
improves both random-access and sequential performance, this is likely to continue. Once
the domain of high-end SCSI drives, 7200 RPM spindles are now standard on mainstream
IDE/ATA drives. A 15,000 RPM SCSI drive was announced by Seagate in early 2000.
- Form Factor: The trend in form factors is downward: to smaller and
smaller drives. 5.25" drives have now all but disappeared from the mainstream PC
market, with 3.5" drives dominating the desktop and server segment. In the mobile
world, 2.5" drives are the standard with smaller sizes becoming more prevalent; IBM
in 1999 announced its Microdrive which is a tiny 170 MB or 340 MB device only an
inch in diameter and less than 0.25" thick! Over the next few years, desktop and
server drives are likely to transition to the 2.5" form factor as well. The primary
reasons for this "shrinking trend" include the enhanced rigidity of smaller
platters, reduction of mass to enable faster spin speeds, and improved reliability due to
enhanced ease of manufacturing.
- Performance: Both positioning
and transfer performance factors are improving. The speed with which data can be
pulled from the disk is increasing more rapidly than positioning performance is improving,
suggesting that over the next few years addressing seek
time and latency will be the areas of
greatest value to hard disk engineers.
- Reliability: The reliability of hard disks is improving slowly as
manufacturers refine their processes and add new reliability-enhancing features, but this
characteristic is not changing nearly as rapidly as the others above. One reason is that
the technology is constantly changing, and the performance envelope constantly being
pushed; it's much harder to improve the reliability of a product when it is changing
- RAID: Once the province of only high-end servers, the use of multiple disk arrays to improve performance and reliability
is becoming increasingly common, and is now even seen in consumer desktop machines. Over
the next few years I predict that RAID will become the "next big thing" as the
thirst for performance increases, and in five years we may see new PCs commonly shipping
with multiple hard disks configured as an array.
- Interfaces: Despite the introduction to the PC world of new interfaces
such as IEEE-1394 and USB (universal serial bus) the mainstream interfaces
in the PC world are the same as they were through the 1990s: IDE/ATA
and SCSI. The interfaces themselves continue to create new
and improved standards with higher maximum transfer rates, to match the increase in
performance of the hard disks themselves.
and Operation of the Hard Disk Drive
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