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How non-volatile memory express speeds up modern PCs

Non-volatile memory express outperforms SATA at almost every turn, but IT should remember that NVMe does not always work well with older hardware.

NVMe is fast -- it runs up to four times faster than 6 Gbps Serial ATA III -- which makes it an ideal candidate for system/boot disk use on state-of-the-art Windows 10 PCs.

In the near-decade since the first solid state drives (SSDs) were introduced, PC users have gotten comfortable with the speed these circuitry-only devices bring to their desktops. At the same time, there's been a major storage shakeup in data centers everywhere because SSDs offer even more benefits to big-time storage and processing cycle consumers. SSDs only recently started to move bits to the best of their abilities. A move at the physical interface level from Serial Advanced Technology Attachment (SATA) to non-volatile memory express (NVMe) opened the floodgates for systems to read and write bits faster than ever.

The difference is speed

Here are speed results from a common benchmarking tool for storage devices called CrystalDiskMark, with an older mSATA SSD in Figure 1, and a newer NVMe SSD in Figure 2, both from Samsung.

speed ratios for mSATA/M.2 NVMe
Figure 1
speed ratios for mSATA/M.2 NVMe
Figure 2

Both reflect results taken from the same system. The only difference is the type of storage device in use. In general, there's no disputing non-volatile memory express is faster than SATA. The speed difference is greatest for sequential reads and writes for large blocks of data, where the ratio is 6.32 for reads, and 4.23 for writes. Notice also when reading -- the most common form of storage access -- NVMe is at its fastest.

An escape from the tyranny of mechanical media

SATA is a standard technology for attaching a spinning disk or an SSD to a PC. It is designed to line up requests to read or write storage information in a queue, and then grab and service items from that queue as quickly as possible. Its design springs from the rotational delay inherent to accessing a spinning disk, where it not only has to select a platter and a cylinder on a physical medium to read from or write to, but it also has to wait for the sectors of interest to literally "come around" so it can read or write them.

Non-volatile memory (NVM) is a form of solid-state storage that retains its content when the power goes off. In contrast, regular random-access memory (RAM) in a PC only retains its contents when power cycles continuously through its circuitry. NVMe is a type of non-volatile memory that plugs into a computer through the peripheral component interconnect (PCI) express bus. PCI describes a family of high-speed serial computer expansion buses. PCI Express is the fastest and most modern expansion bus and replaces older alternatives, such as PCI, PCI-X and Accelerated Graphics Port.

Non-volatile memory express is much faster than SATA.

The switch from SATA to PCIe allows random memory access for flash memory (including NVM) as well as RAM. SATAs interface and queueing model is based on structuring access requests to accommodate the rotational delay inherent to spinning media, and the need to prioritize read/write requests to be ready when the desired regions on that media present themselves to a spinning drive's read/write heads. For memory, there are no such limitations, and one can handle requests immediately in any order.

Ultimately, this explains why non-volatile memory express is much faster than SATA, even with similar underlying flash memory chips present in both classes of devices. Database and other high-volume data access is measured in Input/Output Operations Per Second (IOPS). There, the contrast between NVMe and SATA devices is, if anything, even greater. It's not unusual for the difference between the two to be 10 times or better in NVMe's favor. As a result NVMe storage devices are popular despite their high costs; it's easy to spend $8,000 or more for a 2 to 6 TB NVMe storage device, whereas its spinning disk analog costs $400 or less. For certain applications -- particularly mission-critical ones -- speed provides a competitive advantage or greatly increases productivity, so the increase in cost is offset by the increase in revenue.

What's the catch with non-volatile memory express?

The PCIe bus has been around for a long time: The first version appeared as a PCI-SIG standard in 2003. The PCIe 2.0 standard was introduced in 2007 and was part of standard PC technology within 12 to 18 months. However, older PCs may have problems accommodating NVMe devices because the motherboard vendor may not feel the need to write a device driver to enable the motherboard to interact with an NVMe storage device. Booting from an NVMe device is even trickier because it requires the computer's firmware to recognize and boot from this kind of storage device well before an operating system ever makes its digital appearance.

PCs more than three years old are unlikely to accommodate NVMe devices of any kind. PCs more than two years old are unlikely to be able to boot from them. Newer laptops and tablets make excellent use of compact NVMe SSDs using the M.2 interface designed for small form factor applications. Desktop PCs and servers may include motherboards with built-in M.2 connectors, but really big storage devices typically use x4 or x8 PCIe connections to support maximum data rates within the machine.

The best value for NVMe for professional users comes from a computer with a motherboard that includes one or more M.2 NVMe connections, each currently able to house up to 512 GB of super-fast SSD storage. Expect to pay up to $400 for such device.

What's the non-volatile memory express user experience like?

Properly set up and configured, an NVMe SSD makes a noticeable difference in system speed. Switching from SATA or mSATA (the compact counterpart to SATA, just like M.2 is for NVMe) to NVMe or M.2, users report boot times dropping from 30 to 60 seconds to seven to 12 seconds. Shutdown times go from 20 to 60 seconds to five to 15 seconds. Applications open, close and run faster; ditto for virtual machines.

NVMe devices are on par with prices for higher-end SSDs and they're significantly faster. If a company already benefited from switching from spinning to solid-state storage, it will benefit from switching from a conventional SSD to its NVMe counterpart.

Next Steps

Will NVMe affect PCIe flash adoption?

How GPT disk layout affects NVMe

Prepare for NVMe flash drives on laptops and desktops

This was last published in July 2016

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