Crucial M4
Micron announced the RealSSD C400 at CES on the 4th January. A development of the RealSSD C300, this SSD is known as the M4, Crucial being Micron’s general consumer arm. Launched one year earlier, the C300 stood out from other SSDS due to its adoption of the SATA 6 Gbits standard which opens the door to theoretical speeds of 600 MB/s, as against 300 MB/s for SATA 3 Gbits. Combined with aggressive pricing and high end random access performance, this was one of the flagship SSDs of 2010.
The M4 is also based on a Marvell 88SS9174 controller but in its BLD2 or BKK2 revision, while the BJP2 is used on the C300. According to Crucial, the firmware is what makes all the difference between the C300 and the M4 and not the controller revision. We actually managed to get hold of a 256 GB version in the BLD2 and BKK2 revision and performance levels were identical. It came with a 256 MB DRAM cache, compared to 128 MB on the C300, and the memory used is now 25nm IMFT, while it was 34nm IMFT before.
Here are the figures announced by Crucial in terms of performance:
Read speeds are up 16.9% at equal capacity. Write speeds are up by between 26.7 and 20.9%. Although random writes are also up (+11.1 to 33%), the same can’t be said for random reads: 60,000 IOPs on the C300 but just 40,000 IOPS on the M4.
The Crucial M4 128 GB tested combines a Marvell 88SS9174 controller, a Micron DRAM chip and 16 Micron 29F64G08CFACB flash chips. These chips are engraved at 25nm and combine two 32 Gb dies. The pages are 4 KB in size and a block is 1 MB.
The Crucial M4 256 GB uses different flash chips to the 128 GB version and has 29F128G08CFAAB chips instead. Their capacity is doubled as they use two 64 Gb dies. This time the pages are 8 Kb and the blocks 2 MB.
On the Crucial M4s, 6.9% of the flash memory is used for wear leveling and internal optimisations, which corresponds to the difference between the size of the flash chips (given on a basis of 1 KB = 1024 bytes) and the capacities of the SSDs (given on a basis of 1 KB = 1000 bytes).
