Crucial M550 in Detail
We’ve got three versions of the M550 drive for our tests: 256 GB, 512 GB and 1 TB. It means we can check out the difference between the two varieties of the new platform: with 64- and 128-gigabit flash memory dies. Let’s take a look at the SSDs first, starting from their packaging.
Crucial ships its new SSDs in a nice-looking box with a dark blue cover. There’s a picture of the drive, its logo and series name on the packaging. The capacity of the SSD is mentioned, too. There’s little information on the back of the box but you can learn that the SSD comes with a plastic frame that lets you increase its thickness from 7 to 9.5 mm if necessary.
The M550 series is no different from the M500 externally. The SSD has an aluminum case with rough silvery surface. It is 7 mm thick. The sticker on the face side of the case has become a deeper color. The panels of the case seem to be too thin as they cave in under pressure, yet they protect the internals of the drive well enough.
The PCB is familiar as its layout has remained unchanged since the M500. That’s where the M550 and M500 series coincide the most.
Here’s the PCB of the 256GB M550 model:
The drive is based on the new 8-channel Marvell 88SS9189 controller which is connected to 16 Micron NW631 memory chips (MT29F128G08CECDBJ4-10:D). Each of the latter contains two 64-gigabit 20nm MLC NAND flash dies with ONFI 2.0 interface, so the controller can use 4-way interleave on each channel. That’s one of the fastest internal design variants, so the Crucial M550 256MB is almost as fast as its larger-capacity cousins.
Next to the controller, there is a 512MB LPDDR2-1066 chip that serves as a buffer for storing an address translation table and firmware. The Crucial M500 had faster DDR3-1600 memory for that but now the manufacturer focuses on minimizing power consumption rather than maximizing performance. In this particular case, the effect isn’t negative, though. The M500 design doesn’t use SDRAM for data caching. This buffer is only required for the controller’s housekeeping purposes.
The 512GB Crucial M550 has almost the same PCB as the 256GB version:
We can see the same Marvell 88SS9189 controller and 512 megabytes of LPDDR2-1066 SDRAM. The PCB wiring is identical, too. The only difference is about the flash memory chips. There are 16 of them too, but the marking of Micron NW386 (MT29F256G08CECABH6-10:A) indicates that each chip contains two 128-gigabit 20nm MLC NAND dies. So the 512GB M550 is very similar to the same-capacity M500 in its internal design.
Since the 256GB and 512GB versions of the M550 use flash memory chips with different dies, both versions have 32 MLC NAND devices and have the same internal design. In either case the 8-channel controller can use 4-way interleave, so these SSDs should be close in performance.
The third version of the M550 we’ve got has a capacity of 1 terabyte. It is similar to the others in its internal design, too.
There are only two differences from the 512GB version. First, the amount of buffer memory is increased to 1 GB, so there is not one but two 512MB LPDDR2-1066 SDRAM chips. They are located on both sides of the PCB. And second, each flash memory chip contains four 128-gigabit dies, so they are marked as NW593 (MT29F512G08CKCABH7-10:A). The SSD controller can use 8-way interleave in the 1TB version of the drive but the effect is small: the 1TB and 512GB versions have the same basic specs.
Each M550 series product comes with a 3-year warranty. The specified endurance is 72 terabytes or about 66 gigabytes of written data daily. This rather low value is due to the market positioning of the new series. Micron’s 20nm MLC NAND flash is rated for 3000 rewrite cycles, so Crucial’s new SSDs are going to be able to write about 10 times more data than specified.