Suppliers are combining flash memory with traditional
hard discs to create hybrid drives with data transfer rates
suitable for high-performance software
One of the greatest usability issues with PCs is the time it
takes to boot up the operating system and load applications.
It takes ages, and it is clear that it must have been planned
that way. After all, the PC is 25 years old this year, and if
manufacturers wanted to solve the problem, they would have done it
by now. So, rather than a system flaw, sluggish data transfer is a
cleverly designed feature.
Or maybe there is another explanation.
Intel’s research shows that over the past 10 years, CPU
performance has increased 30-fold, while hard drive performance
only increased by a factor of 1.3.
The problem is that hard drives are mechanical, and while
companies have had great success at driving efficiencies into
semiconductors, mechanical devices are still bound largely by the
laws of physics.
It is possible to reduce the fabrication size on a CPU, split it
into multiple cores, and pump up the clock speed.
But hard drive manufacturers cannot suddenly make a 7,200rpm
hard drive spin at 50,000 rpm – not unless you want your PC to
start walking across the floor.
And yet, thanks to companies like Microsoft, software continues
to become more complex and bloated. CPUs have done a good job of
running larger programs, but the data transfer rate from the hard
drive has remained relatively static – hence the increasing load
times.
So what can be done about it? If it is not possible to get rid
of mechanics altogether, the logical answer is to enhance them
using high-performance silicon. Thus, the hybrid drive was
born.
The hybrid drive takes a conventional hard drive and puts some
nonvolatile Nand flash memory on it, which serves both as a write
buffer and a storage mechanism for critical boot and resume
data.
The drives are designed to be used with Windows Vista, which
includes a feature called Ready Drive, which is designed
specifically to support them.
When booting up or resuming from sleep state, there are certain
system files that Windows needs to recover itself to a usable
state. Traditionally, these have been stored on the hard drive just
like everything else. Vista will store these critical files in the
nonvolatile memory cache.
Because there are no mechanics involved, the data transfer rate
is therefore much faster, and this will bring the operating system
into system memory much more quickly.
Seagate’s product marketing manager for notebook and desktop
computing, Joni Clark, predicts a 20% improvement in resumption and
boot times.
“Also, on the application response times, we could see up to a
three-fold improvement in Vista,” she adds, saying that crucial
application files are likely to be stored in the nonvolatile cache
as well.
Microsoft says it will use its Super Fetch technology to
augment the use of the hybrid drive cache. Super Fetch works by
predicting which memory pages need to be retrieved, rather than
simply retaining the most recently used system memory pages in
cache Ram.
“Super Fetch profiles the page usage, and for each of those
memory pages it tracks the access patterns, how it is used, where
it is used, and in what context,” says Gabriel Alul, group program
manager at Microsoft.
“The cool thing about that is that it can be very predictive,
even across complex user scenarios.”
Super Fetch is unlikely to be restricted purely to Nand flash
memory, however. It will take advantage of the volatile DRam cache
memory on all modern motherboards.
“Vista uses the Nand memory as an overflow,” explains Kishore
Rao, product line manager for Robson, a flash memory technology
under development at Intel.
But the memory on a hybrid drive has advantages other than
speed. In addition to guessing which system and application files
you will need and keeping them in cache memory for faster
retrieval, it will also drastically reduce the active spin time of
a hard drive.
Vista will automatically recognise a hybrid drive and use part
of its cache memory as a write buffer.
Even when using applications such as Microsoft Word, Windows is
often writing small blocks of data to the hard drive, such as log
files and automatic Microsoft Word back-ups.
This steady trickle of data means that the hard drive in the
average notebook is spinning for most of the time, so it is ready
to write the next block of data when it arrives. Spinning a piece
of metal at high speed drains power.
Instead of writing that data to the hard drive, a Vista system
equipped with a hybrid drive will write it to the drive’s cache
memory until it is full.
Because it is writing to the cache memory rather than to the
drive, the drive can be spun down. When the cache memory fills up,
Vista spins up the drive and flushes the cache to the hard disc
before spinning it down again.
Storing frequently-used system data in the cache will also save
power because you do not have to spin up the drive to read
application and system data, says Andy Yang, strategic marketing
manager at Samsung.
He adds that if you can keep a hard drive spun down 90% of the
time, you will be able to reduce its power consumption by the same
amount.
As a hard drive takes up about 15% of total system power, this
tallies with Seagate’s estimate that a hybrid drive will extend
notebook battery life by about 12%.
Keeping the hard drives spun down will also increase
reliability, say the suppliers. The drives run at lower
temperatures, and isolating read-write activity reduces the risk of
head crashes.
However, there is a caveat: Nand memory has a limited number of
read-write cycles, after which the memory becomes unreliable.
Could this be a problem?
Suppliers are getting around this by using software algorithms
including error correction and “wear levelling”, which ensure that
different blocks of Nand memory are used equally over the lifetime
of the device. This will help to mitigate the damage to the
memory.
Seagate will supply its Momentus PSD hybrid drive with a
five-year warranty, says Clark. The expected mean time between
failure of the Nand memory will be more than offset by the reduced
wear and tear on the drive mechanism, she says.
The power-saving and reduced risk of head crashes with the
drives is causing manufacturers to focus on the notebook
market.
Both Seagate and Samsung plan to release notebook versions of
their hybrid drives early next year, but neither have ruled out
producing versions for desktop machines and, in the future, for
servers.
This would make sense. Very short boot and resume times are a
key component in Microsoft and Intel’s Media Centre PC
proposition, and many business desktop users would be only too
happy to forego their mandatory morning boot-up coffee break.
In the server world, increased system performance is always
tempting. But will PC system builders and users want these
drives?
One danger is that, in a market with razor-thin margins, someone
will have to swallow the admittedly small cost of the extra Nand
flash memory, says Joseph Unsworth, principal analyst in Gartner’s
semiconductor team.
Notebook margins may be slightly less constrained that desktop
margins, but it will nevertheless add complexity to system
builders’ inventory, he warns, which many will not like. On the
other hand, they may not have a choice.
“For laptops, beginning June 2007, if an OEM wants to get a
Vista premium logo for a laptop, they will have to get that hybrid
drive built in,” says David Weeks, Windows client marketing
manager at Microsoft UK.
Perhaps, but the waters are muddied by another option: Robson.
Robson is Intel’s stab at a Nand cache. It may not manufacture hard
drives but, like Samsung, it does manufacture Nand flash
memory.
Intel is putting this memory – between 256Mbytes and 4Gbytes –
on the Santa Rosa chip set, designed specifically for notebooks and
due for release early next year, to do just what the hybrid drives
are doing.
“It introduces Nand memory as a cache solution between the DRam
and the hard drive,” says Rao, who seems to read from the same list
of benefits as Samsung and Seagate.
What is not yet clear is whether Microsoft would consider
allowing Robson technology to replace a hybrid drive and fulfill
the logo certification requirements, but Intel is preparing to
accommodate both devices on a motherboard.
“Microsoft is very interested in Robson technology. We are
looking at it closely to ensure that we meet their requirements for
non-volatile memory,” says Rao.
What few people have thought of here is security.
Security conscious organisations are taught to be very aware of
data left on hard drives when PCs are disposed of. However, Nand
memory is nonvolatile, so a company could end up with up to
512Mbytes of data lying around in memory on the motherboard or on
the side of the drive.
Few companies own the industrial-scale degaussing equipment that
can instantly be used to fry the data on a drive, and instead rely
on software that laboriously overwrites the magnetic surface.
One possibility is that Vista could encrypt the data written to
the Nand cache, but that is not certain. “Support for a secure
erase capability handling the cache will be supplier-specific,”
says Yang.
Hybrid drives could solve the age-old problem of system
performance, especially at boot-up. That will be useful for
notebook users, who are constantly hibernating and starting their
systems.
It could breathe new life into a mature technology.
Solid state: The future
Replacing the hard drive altogether with solid-state storage
will provide significant performance benefits, but its high cost
means it is restricted to niche devices and applications.
The military is a heavy user of solid-state discs, but it is also
moving into devices such as ultra mobile PCs. Samsung will sell a
version of its Q1 UMPC with a 32Gbyte solid state drive, but the
premium is high.
However, Nand costs are falling rapidly, according to Gartner, and
analyst Joseph Unsworth says that 32Gbyte Nand discs could cost
less than £30 by 2009 – less than the cheapest hard drives.
IBM is enthusiastic about storage-class memory. Its Almaden
research company is experimenting with three-dimensional memory
storage at manufacturing sizes of 32nm and below, using techniques
such as self-assembly and nanoimprint lithography. It predicts
significant developments in three to five years.
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