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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