Solid state of the nation

NAND flash technology has come of age

There's nothing that Seagate, Hitachi or Western Digital can do about it.

Those giants of the spinning disk world must be quaking in their boots. The flash storage revolution is coming and it could well wipe that last bastion of ancient mechanical technology from the face of the PC world.

Opto-mechanical drives have always been an aberrant part in the PC. Despite the perfection of their mirrored spinning platters, the hard drive - even the latest 750GB capacity gorgons - is a real performance bottleneck, not to mention a serious power drain when it comes to mobile systems.

A replacement for hard drives has been expected. In the past we have looked at two of the early solid state drives and found them lacking, though at the time we said the promise of performance was there. Today, with Intel and Samsung getting into the act with hybrid drive technologies and entire replacement drives; the solid state drive is here.

Flash bang

We're all familiar with NAND flash technology. USB thumb drives, memory cards and music players like the iPod Nano all use NAND-based flash memory. It's a cheap, solid state memory technology that's suited to a storage role, as it's accessed in a sequential manner with data stored in blocks of pages.

It has higher access speed than other solid state technologies - such as NOR - and a longer lifespan of at least a million rewrites, if not three million plus. As with spinning disks, NAND-based drives can suffer bad blocks.

Error correcting and bad block mapping can be performed on the fly; when a bad block is detected it'll be marked and won't be used again, and data will be moved to a free area. Flash chips are grouped together to build up capacity.

Currently Samsung is producing individual 8GB chips, and these can be used together to produce drives of higher capacity. It seems four is optimal, with Samsung opting for a 32GB IDE flash drive, while www.adata.com has a 128GB drive that utilises a SATA interface in a 2.5-inch drive package.

Using Moore's law as a guide 2,568GB and 512GB flash drives should be common by 2010,and be large enough for a system boot drive. Fast access times are a feature, even early devices showed access times in the points-of-milliseconds level, compared to traditional drives that peak at ten milliseconds.

Spinning discs can only read what's currently under the single read head array. If it misses the data, the platter makes another revolution, that's on top of the time taken to get the head into position initially. There are a few very common situations that cause spinning drives real trouble because of this behaviour. The first is when it's trying to load lots of small files dotted all over the drive.

The second is trying to deal with a badly fragmented drive. The third is when multiple tasks are trying to access data from all over the drive. All of these result in drive thrashing. If this is happening, a drive with a sequential speed of 100MB/s plus is pointless. Flash memory with a random access speed a hundred times faster than a traditional drive, can cut through these tasks easily.

Robson lives

With the capacity now making a difference to drive speed, the question is how to implement it, as the unit price is still high. This has resulted in a hybrid solution that's available now in different guises. We'll be hearing a lot about Turbo Memory - previously known as 'Robson' - part of the new Centrino Duo and Pro architecture that we've already reviewed .

The idea behind it is the same as the ReadyBoost technology in Vista and the Samsung 160GB hybrid drive, you take a reasonable-sized lump of flash memory and use it to cache often accessed files.

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