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Custom firmware, cherry-picked NAND
The Intel 520 Series uses the very same SandForce controller available to other drive makers. Tellingly, Intel says it's been testing and validating the chip for more than a year now. Other SSD makers started pushing out drives as early as last spring, and the volume of user complaints and firmware updates that followed make a good argument for Intel's conservative approach.

By the fall, new firmware code from SandForce claimed to fix the infamous BSOD bug. It seems to have done the trick, but Intel's response was measured when asked about BSOD errors during a conference call with the press. The company stated that the 7A and 4F blue screens commonly associated with the BSOD bug were "absolutely going to be extremely reduced" on its 520 Series SSD. That sounded a little too measured, but Intel assured us after the call that this new model has been held to the same quality and reliability standards as its other SSDs. Indeed, the 520 Series is purportedly solid enough to appear in systems sold by "tier one" PC makers—a first for SandForce-based SSDs, Intel says.

Firmware, rather than hardware, seems to have been the culprit behind the SandForce BSOD issue. Those tentative about springing for any SandForce-based drive may find some comfort in the fact that the 520 Series' firmware was "co-defined" with Intel. The firmware enhancements contributed by Intel won't be shared with other SandForce drive partners, making the 520 Series unique in a market filled with largely cookie-cutter designs. Looks like Intel is following the same playbook it did with the 510 Series, which had its own set of exclusive firmware tweaks. Intel wasn't keen on revealing details about the finer points of the 520 Series' firmware other than to say that its garbage collection and NAND management have been improved versus other SandForce solutions.

Intel also differentiates the 520 Series SSD at the NAND level. The chip giant has been making the flash in its own SSDs since the X25-M. Recently, Intel NAND has started appearing in drives from other vendors. Nearly half of the SandForce-based SSDs we've reviewed lately have used Intel flash—specifically, synchronous NAND built on a 25-nm fabrication process.

The very same NAND appears on Intel's own 520 Series SSD, but the individual dies have been cherry picked for the drive. When your fabs crank out a steady stream of 25-nm NAND, you have the luxury of sorting through it and saving the best stuff for yourself. Intel has several grades of 25-nm NAND, including one sold to other drive makers and a high-endurance variety reserved for enterprise-grade SSDs.

All of the models in the Intel 520 Series lineup use 64Gb NAND dies. The number of dies ramps up with the total storage capacity, and the higher-capacity models have more dies per package. Only one die is squeezed into each NAND package for the 60GB model, while there are two dies per package for the 120, 180, and 240GB variants. The 480GB model has four dies per package. These details are important because we've found that NAND die configurations can have a big impact on SSD performance, especially with SandForce-based drives.

Intel's spec sheets for the 520 Series set some expectations for the relative performance of different models in the lineup. They also highlight the performance deltas one can expect going from compressible to incompressible data. SandForce-based SSDs only achieve their peak write performance with data that's amenable to compression. Here's how the performance ratings for the 520 Series stack up:

Capacity Max sequential (MB/s) Max 4KB random (IOps) Price
Compressible Incompressible Compressible Incompressible
Read Write Read Write Read Write Read Write
60GB 550 475 430 80 15,000 23,000 12,000 6,900 $149
120GB 550 500 550 150 25,000 40,000 24,000 13,000 $229
180GB 550 520 550 170 50,000 60,000 46,000 13,000 $369
240GB 550 520 550 235 50,000 60,000 46,000 16,500 $509
480GB 550 520 550 275 50,000 42,000 46,000 9,500 $999

As you can see, sequential and random write performance take a big hit with incompressible data. Intel contends that 75% of the file types accessed by "typical office user[s]" can be compressed by "60% or more," so real-world performance should fall somewhere between the two extremes. PC enthusiasts deal with a lot of data that's already been compressed—music, image, and video files, for example—but most of those files probably reside on secondary mechanical storage. There isn't much benefit to having one's MP3 collection sitting on an SSD.

While the Intel 520 Series' performance ratings climb with the capacity, the 480GB model's random-write performance is purportedly lower than that of its 240GB sibling. Intel says higher-capacity SSDs can be slower due to the larger address space required to cover additional storage. That issue apparently doesn't affect sequential write speeds, which ramp up by 40MB/s for the top model, at least with incompressible data.

Before we move on from the table, check out the prices on the right. Those are for 1,000-unit quantities, so street prices won't necessarily be lower. Ouch! Comparable SandForce SSDs with 240GB of synchronous NAND can be found selling for less than $400 these days. 120GB models have fallen under $200, and their 60GB siblings are routinely listed at around $100.

Intel is no stranger to selling SSDs at premium prices, and the 520 Series' five-year warranty at least justifies some of the additional cost. Most solid-state drives, including all of the SandForce-based designs we've seen, are covered by three-year warranties. Longer warranties don't guarantee better reliability, of course, but Intel points to this article as evidence of the low return rate of its SSDs. Intel says the failure rate of the "millions" of its SSDs out in the wild is less than the company's 0.75% target.

If the promise of better reliability isn't enough to cover the added expense associated with the 520 Series, perhaps software will help. We first played with the new version of Intel's SSD Toolbox software at IDF in September. The application comes with 520 Series SSDs and provides an easy way to secure-erase drives and update their firmware. Intel includes a handy life meter to give users a sense of how many write-erase cycles are left in the flash. There's also a TRIM-powered optimizer that can be set to run on a schedule if you don't want to wait for the drive to empty eligible flash pages on its own.