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Tech Primer
Hybrid hard disc
What is a hybrid hard disc?
 A
hybrid hard disc combines a magnetic hard disc drive and flash memory on a single
device. Flash is popular in consumer storage and is used in cameras, MP3 players,
USB drives and mobile phones. On the other hand, hard discs have an advantage
over flash in terms of capacity—the density of magnetic drives continues
to grow as the price per gigabyte falls. With the hybrid HDD, manufacturers
seek to combine the robustness, low-power consumption and speed of flash media
with the storage density and low cost of magnetic drives.
Who is working on this technology?
It is a joint effort of Microsoft and Samsung. Microsoft’s hybrid hard
disc design features a non-volatile (NV) cache added to the hard drive to store
frequently-used sectors for fast boot and resume times. The hybrid drive, designed
to work with the upcoming Windows Vista OS, is being exhibited for the first
time at the Windows Hardware Engineering Conference (WinHEC) in Seattle, USA,
from April 25-27, 2006. The hybrid hard drive architecture incorporates a small
OneNAND device from Samsung. The ultra-high-density benefits of magnetic storage
technology are preserved, while the ultra-low-power, ultra-high-reliability
and fast read/write access of advanced NAND technology (such as OneNAND) enhances
the overall value of the hybrid drive at little or no additional cost. A cache
size of at least 128 MB is recommended, but drive manufacturers could conceivably
incorporate caches as large as 4 GB or more to store critical system data or
frequently accessed portions of the operating system.
What are its advantages?
A hybrid drive saves power by keeping the spindle motor idle most of the time,
while the operating system writes to the OneNAND write buffer. On a laptop,
the power savings could add up to an hour of additional battery life. Faster
boot and resume is another advantage. Booting straight from the flash cache
eliminates latency without sacrificing disc performance; flash can nearly saturate
the SATA protocol’s throughput.
How is flash integrated into a normal hard disc?
There are three ways of integrating non-volatile memory into hybrid HDDs. The
first involves an embedded flash disc, which requires a NOR interface. The second
is the use of raw NAND flash with the existing HDD controller. The third is
the use of a raw NAND with a NAND controller.
For further information see
www.samsung.com/Products/HardDiscDrive/news/HardDiscDrive_20050425_0000117556.htm
www.extremetech.com/article2/0,1697,1902075,00.asp
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