The Advantages of PCIe SSDs Over SATA Drives
Interfaces on a computer motherboard operate at different speeds. Just like the internal components of a computer communicate faster than something connected over USB, there are different bandwidth limits to internal interfaces. SATA has been the main interface used to connect hard drives to a motherboard for several years. It works well, and with conventional magnetic-platter hard drives, SATA can’t max out its transfer capabilities. However, SSD technology can. SATA relies on internal wires running from a drive to ports on a motherboard. It’s not all that direct, but it gets the job done and allows for flexibility in drive placement. PCIe is the high-speed interface used for components like graphics cards that require massive amounts of data bandwidth at extremely high speeds. PCIe devices plug into the motherboard and pass data more directly to the CPU at a higher rate. With PCIe, SSDs are more limited by their ability to read and write than their ability to transfer data.
How Much Faster Is a PCIe SSD?
The current iteration of SATA is SATA III. It supports a theoretical top speed of 6 Gb/s, which works out to about 600 MB/s of data transfer. PCIe is a little more complex to break down. First, there are PCIe 1.0, 2.0, and 3.0 sockets. Version 3.0 is the newest, but version 2.0 slots are found on some motherboards. If the board is a PCIe 3.0 board, you must factor lanes. PCIe connections are split into lanes. There are usually four-lane, eight-lane, and 16-lane sockets, and you can identify these by size on the board. The large 16-lane ones are where a graphics card is plugged in. PCIe 3.0 has a theoretical speed of 1 GB/s per lane, meaning a PCIe 3.0 x16 socket has a theoretical cap of 16 GB/s. That’s a high amount of speed for a hard drive. A usual PCIe SSD more likely uses four or eight lanes, but the potential is still better than SATA. Those numbers are theoretical, and not what your practical performance will look like. If you take a look at real SSDs, the speeds advertised are more grounded, but the benefit is still evident. The Samsung 860 EVO claims a max sequential read speed of 550 MB/s and a max sequential write speed of 520 MB/s. The closest comparable PCIe drive, the Samsung 960 EVO, has a reported 3.2 GB/s max sequential read speed and 1.7 GB/s max sequential write speed. It only uses four PCIe lanes.
NVMe and M.2
Two more terms are discussed with PCIe drives: NVMe and M.2. M.2 refers to a PCIe form factor designed specifically for SSDs. M.2 is more compact than standard PCIe, and only accepts M.2 form factor devices, which are exclusively hard drives. M.2 was designed to provide an interface to allow SSDs to use a PCIe interface without interfering with, or taking slots from, more typical PCIe devices like graphics cards. M.2 is also common in laptops because it usually lies flat into the motherboard, taking up little space. NVMe stands for Non-Volatile Memory Express. Non-Volatile memory is any type of storage memory. Volatile memory refers to something like RAM that’s overwritten continuously and doesn’t remain after a reboot. NVMe is a protocol designed specifically for PCIe hard drives to allow the drives to communicate quickly. The goal of NVMe is to get SSDs to behave more like RAM because RAM uses similar technology and moves faster than SSDs.
