What is it about solid state drives that excites such emphatic claims? SSDs use non-volatile NAND flash memory...
to store data and access it very much faster than rotating hard disk drives, and with an infinitesimal risk of mechanical damage that can cause data loss. But they have a trio of negative characteristics.
- Unlike hard drives, with solid state drives you need to delete data before writing new data. Two cycles are needed, rendering solid state drives slower to write data than to read it.
- Solid state drives wear out; the ability of a flash cell to be rewritten declines over time until it simply stops accepting new data. In comparison, hard drives go on forever.
- Solid state drives are accessed in quite large chunks of data -- typically 4 KB at a time -- whereas a hard drive is accessed 512 bytes at a time. Applications and system software tailored to hard drive access can use SSDs inefficiently, wasting much of the SSD's speed.
Windows in flash doesn't boot too fast
Flash SSDs were added to notebooks without anyone carrying out, or making public, any thorough tests of whether these SSDs delivered I/O acceleration and prolonged battery life. Once news of real-life disappointments started coming in, magazines started tests and the surprising results were that battery life extension was sometimes non-existent and I/O speed-up patchy and often trivial. Specifically, Windows in flash didn't boot appreciably faster than from a hard drive.
SanDisk boss Eli Hariri has said Vista needs changing to make better use of flash. It reads data in chunks that are too small and so reads the same page of flash data again and again.
Real-world battery life results were equally surprising. A closer look showed that flash actually uses quite a lot of power.
Flash used only for notebook "extremes"
The result of the speed-up disappointment and power profligacy is that flash is now only being used for notebook extremes, the high-end MacBook Air and low-end Asus Eee netbook type products. Both need the lightness of flash and, with netbooks especially, its greater reliability, while the supposed speed and battery life extension is less important.
Both Lenovo and HP have added high-end notebooks with flash. Lenovo's new ThinkPad X301 doesn't have a hard drive option. It ships only with solid state storage in 64 GB or 128 GB capacities and costs from £1,880 for the privilege. It uses a better flash controller than before and gets a top-of-the-class gold rating from the US EPEAT environmental rating organisation. HP is less enthusiastic about flash and only offers an 80 GB SSD option alongside various hard drives for its high-end Elitebook.
For the notebook mainstream, flash is currently a waste of time, being insignificantly faster than hard drives, no good for extending battery life and too expensive to justify its reliability over hard drives prone to breakdown. Currently flash stores one binary digit per cell. Multi-layer cells (MLCs) will store, initially, two and then three bits per cell and bring the cost per flash GB down. But flash will still be more expensive than hard drives, so, unless a new generation of flash memory actually does speed up apps or extend battery life, it's hard to see it encroaching much on mainstream notebook hard drive use.
This may happen. Intel and Micron have both announced flash that can do sustained read I/O at 240/250 MB/sec which is almost 100 MB/sec faster than the current average OCZ/Super Talent/Samsung SSD used in notebooks. That may well start to significantly shrink Windows boot time and accelerate Office applications as well as intensive disk-bound photo-editing and DTP applications.
The new controllers used in the Intel and Micron flash as well as new generation controllers from OCZ, Super-Talent and others will help boost power efficiency and extend write endurance time so the flash doesn't wear out before the notebook gets changed.
The time for mainstream notebook flash use is not yet upon us. But that time may be coming, as new power-efficient and fast controllers are taken up by notebook manufacturers. As soon as the notebook flash acid test -- faster Windows startup -- is passed and flash is less than 10 times the cost per GB of hard drives – with the arrival of MLC flash chips, the mainstream flash notebook era will have begun. In five years time hard drives may disappear from notebooks. Flash will have crossed the notebook chasm and hardware, once again, will have rescued us from Windows bloat. Bring it on.
About the author: Chris Mellor has been active in storage writing for many years, editing the UK's first print storage magazine, then its first dedicated online storage news channel, and is the founder of Blocks and Files.