SSDs have been pushing the bandwidth limits of SATA 6Cbps for some time, and even recent PCI-E based M.2 and expansion card SSDs are still held back by the Advanced Host Controller Interface (AHCI), the protocol that specifies how a storage device communicates with the system host controller. It was designed for older mechanical drives, but it's inefficient for SSDs and wastes CPU cycles. That's where the Non-Volatile Memory Host Controller Interface Specification (NVM Express or NVMe for short), used by Intel's new SSD 750 card, comes in.
Unlike AHCI, NVMe is designed specifically with PCI-E SSDs in mind, capitalising on their inherent parallelism and low latency. For starters, NVMe introduces significantly larger queue-depth support - AHCI supports a single command queue with 32 commands, while NVMe can support 64K queues, each with 64K commands. This setup helps to ensure that NVMe takes full advantage of the multiple CPU cores in today's systems, whereas AHCI was mostly limited by single-core performance.
The uncacheable register accesses per command have also been greatly reduced, cutting latency. Command parameters can now be received in one 64-byte memory fetch rather than two with AHCI as well. Essentially, NVMe allows CPU cores and SSDs to do more at once, with less latency between them.
Intel's SSD 750 is the first consumer NVMe drive. It communicates directly with the CPU via four PCI-E 3 lanes (up to 32Gb/sec). It's available in 400GB or 1.2TB capacities and as a 2.5in drive that uses the new SFF-8639 connector or, as with our sample, a 4x PCI-E card. It promises sequential read and write speeds of up to 2.4GB/sec and 1.2GB/sec respectively, and respective random read and write performance of 440,000 and 290,000 IOPS.
The drive targets enthusiasts and workstation users with demanding storage needs, rather than average home users or gamers. An important feature for the target audience is the full power loss protection afforded by the on-board capacitors, with all in-flight and cached data protected. The five-year warranty also covers a hefty 219TB written endurance rating, or 120GB per day - a serious workload.
Then we have the card's 18-channel Intel CH29AE41AB0 controller, which is already taking great advantage of parallelism; the vast majority of SATA controllers have just eight channels. To make up the 1.2TB capacity, there are 18 NAND packages on the front of the PCB, each with four IMFT 128Gb NAND dies inside them, and 14 single-die packages on the rear. The reason for this disparity in die count is that the front chips are cooled by the drive's heatsink, which is necessary as the drive can consume up to 25W when it’s fully active. It also consumes 4W when idle, so we're unlikely to see this card in smaller, mobile-centric form factors.
Intel's Z97 and X99 chipsets support NVMe, although your motherboard may need a BIOS update first. The latter chipset is especially good for NVMe drives, thanks to its 40 PCI-E 3 lanes - enough for two SSDs and two graphics cards to run at full bandwidth. Z97, however, is limited to 16 lanes, so you'll lose some available graphics bandwidth if your motherboard doesn't have a PLX PCI-E lane switch, which you usually only find on high-end motherboards.
You'll also need Windows 7 or later, and Intel has released its own driver for the SSD 750, which is faster than the NVMe one that's built in to Windows 8.1. NVMe drivers are also available for Linux, ChromeOS and FreeBSD, and the drive is bootable if your motherboard is running UEFI 2.3.1 or later. RAID 0 configuration can be achieved too, but only through software, so it wouldn’t be bootable. Support for true, hardware-level NVMe RAID will come in future chipsets.
Performance
The SSD 750 dominates nearly all of our benchmarks, and is clearly capable of achieving the advertised speeds - in particular, the sequential read and write speeds are phenomenal. It's leagues ahead of SATA performance in every test except single-queue-depth reads, although it's still fast here too.
Even in PCMark 7 and 8, which use traces of software not optimised for NVMe, the SSD 750 has the best result in each test. That said, the differences are small and often inconsequential - in games and standard office apps, you're unlikely to notice any difference, although more demanding tasks such as heavy photo and video editing may be met with a small but appreciable speed bump.
Where it all comes together is in Iometer testing, which batters the drive with high-queue-depth, random read and write workloads typical of various professional and workstation environments. NVMe was designed to accelerate these workloads, and it works a treat; overall, the SSD 750 is almost five times faster than the Samsung SSD 850 Pro, which is the best SATA drive available for this work.
The Windows 7 boot times are the only letdown, and here we suspect the lack of native OS support is to blame - we had to point the OS installer to the Intel driver just to recognise the drive. If you want to boot from this drive, Windows 8.1 should be used.
Conclusion
Clearly, NVMe is a turning point for flash-based storage, but at over £800, or around 73p per usable gigabyte, it comes with a high cost of entry. Still, many professional and workstation workloads will see a dramatic increase in throughput, which could well justify this price.
Average home users and gamers are unlikely to notice the difference, but if you're an enthusiast who wants the fastest storage system available, we recommend turning to the 400CB model - if s slightly slower, but the £300 price tag is much more palatable. MATTHEW LAMBERT
VERDICT
NVMe has made a seriously impressive debut in the SSD 750, but at this price, only wealthy early adopters and workstation users need apply.
SPECIFICATIONS
Interface PCI-E 3.0 x4 (32Cbps), NVM Express
Nominal capacity 1.2TB
Formatted capacity 1,117.81GB
Controller Intel CH29AE41AB0
Cache 2GB Micron DDR3
Memory IMFT 20nm MLCNAND
Warranty Five years (219TBW)