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A few more tweaks at 34nm
More important than changes to the X25-M's performance ratings are the steps Intel has taken to combat the scourge of long-term SSD performance: the block rewrite penalty. This penalty arises due to the nature of flash memory cells, which are made up of 4KB pages organized into 512KB blocks. It's possible to write to pages directly, but only if they're empty. When writing to an occupied page, the drive must rewrite the entire block. Doing so involves reading the much larger block into cache, modifying its contents, and then writing back the whole thing—additional steps that take time, slowing write performance.

But a solid-state drive with loads of free storage capacity should have plenty of vacant pages ripe for direct writing, right? Unfortunately, no. When Windows deletes a file, it doesn't require that the associated data be wiped from the drive. The flash pages in question are marked as available, but their actual contents go untouched, so they're technically still occupied. Thus, even in normal day-to-day use, one will eventually exhaust a flash-based drive's supply of fresh pages and be forced to suffer through the block rewrite penalty for each and every subsequent write.

Intel uses a couple of approaches to combat performance degradation over time. The first is a series of garbage collection algorithms that are constantly working to cleanse the drive of internal fragmentation. Latency reductions inside the new X25-M storage controller apparently benefit these algorithms. Intel says the new design's larger cache helps, too, as do improvements to the storage controller's ability to perform concurrent operations and to the efficiency of its NAND array management.

The second stage of Intel's block-rewrite defense comes in the fourth quarter of this year in the form of a firmware update with TRIM support for Windows 7. TRIM will address the block rewrite penalty by requiring that flash pages associated with deleted files be emptied rather than simply marked as available, keeping drives topped up with unoccupied pages.

Unfortunately, Intel has no plans to offer a TRIM-capable firmware update for its 50nm SSD family. The drives are nearly a year old now, and the TRIM specification wasn't even close to being finalized back then, so Intel's position is defensible. Still, it irks me a little that TRIM support perhaps could be added to the old drives with little effort.

Packaged with the 34nm TRIM firmware update will be an Intel SSD Toolbox application with a "TRIM-style" manual cleaning utility for both Windows XP and Vista. Indilinx offers a similar "wiper" utility for its drives, although that tool has compatibility problems with storage controller drivers from AMD, Intel, and Nvidia. Let's hope Intel's app is more robust.

The second-gen X25-M's extensive under-the-hood changes are capped by a new skin. Gone is the black exterior of the old drive; in its place is a bare metal casing that's gone unpainted in an attempt to further reduce costs. A black metal shim has been added to bring the drive up to a standard 9.5-mm thickness, though.

It's a good thing that there's a color contrast between the old and new models, because Intel intends to produce both as its customers make the transition to the new hotness. One may also differentiate between generations based on their model numbers: The old ones end in G1, while the new ones are tagged as G2.

Rumors preceding the X25-M G2's official launch suggested that a 320GB flavor would join existing 80 and 160GB models. There's even room on the barren back of the new 160GB drive's PCB to add another 10 flash chips. Intel has yet to announce a 320GB drive, though, saying only that higher capacities won't come until next year. We'll also get a "high performance" 34nm drive in 2010. I suspect that will be an enterprise-class Extreme model based on single-level cell (SLC) flash.

At least we won't have to wait long for Intel's 34nm flash chips to migrate to its 1.8" drives. An updated X18-M is coming by the end of this quarter, and it has the same performance ratings as the second-gen X25-M.