SSDs (Solid-State Drives) are the most efficient and the fastest storage media of today, with 10 times, or even more, the speed of HDDs. It is largely due to this speed advantage that SSDs are now dominating the storage market. Since 2015, the global shipment of SSDs has been rising while that of HDDs has been slowing down.
Early releases of SSDs were using the SATA interface but because SATA was primarily designed for HDDs, it’s limiting the full potential of SSDs. SSDs needed a much faster interface for optimum performance and manufacturers later on tapped the PCIe interface which significantly gave SSDs a strong boost in performance. Before we discuss PCIe SSDs further, let’s first have an overview of what PCIe is.
PCIe which stands for “Peripheral Component Interconnect Express” is the standard interface implemented on modern motherboards for connecting high-speed components like GPUs, RAMs, and SSDs. Those rectangular slots embedded on your computer’s motherboard where you insert your expansion cards are the PCIe slots.
It serves as the point of connection between the PCIe cards and the motherboard allowing direct communication between the device inserted to the slot and the other components of the motherboard, like the CPU. This shortens the communication path between the components resulting in a faster data transfer rate, making PCIe the interface of choice for most devices.
The physical configuration of PCIe slots depends on the number of lanes they possess. There are currently five PCIe configurations – PCIe x1, PCIe x2, PCIe x4, PCIe x8, PCIe x16. The numbers after x signify the number of lanes each slot supports. The more lanes a slot has, the more data can be transferred to and from the device.
Spanning four generations with two more already in development, PCIe has undergone various innovations to improve the system’s performance. Based on previous implementations, the most recent version usually has twice the bandwidth, twice the gigatransfer rate, and twice the frequency of its predecessor. What’s great about PCIe is its backward and forward compatibility. An old PCIe device can still be used on motherboards with newer PCIe versions and old PCIe interfaces can accept devices employing the newer PCIe standards.
PCIe devices are usually upgraded in parallel with every iteration of the PCIe interface because even though PCIe is both forward and backward compatible, a device’s or the PCIe interface’s full potential can only be achieved if the version of one is the same with the other. The latest PCIe standard currently adopted by manufacturers of both motherboards and peripherals is PCIe 4.0.
PCIe 4.0 and PCIe 4.0 SSD
PCIe’s fourth gen, the PCIe 4.0 is the most recent PCIe standard to hit the market. It has doubled the transfer rate of PCIe 3.0 at 16GT/s and provides up to 2GB/s bandwidth per lane. A PCIe x16 can therefore deliver up to 32GB/s of bandwidth, twice of what you can expect from PCIe 3.0. As of this writing, only AMD and Intel have produced motherboards that support PCIe 4.0. Other manufacturers are also catching up as more and more PCIe 4.0 devices are already being released.
Just like the previous versions, PCIe 4.0 is forward and backward compatible. Your new PCIe 4.0 expansion card can work with your PCIe 3.0 motherboard, but it’s speed will be limited by PCIe 3.0’s capacity. Similarly, if you have a PCIe 4.0 motherboard, your PCIe 3.0 device can still be used on it but it will not max out the PCIe 4.0’s speed because of the device’s lower specs.
One of the devices that greatly benefit from PCIe 4.0’s throughput are the SSDs. Although PCIe 4.0 debuted in 2017, it only became usable with SSDs in 2019 due to lack of PCIe 4.0 SSD controllers at the time. Since then, PCIe 4.0 SSDs have been in production from manufacturers like Samsung, Western Digital, and Adata. Samsung 980 Pro, WD Black SN850, and Sabrent Rocket 4 Plus are just some of the best PCIe 4.0 SSDs already making waves in the storage market.
PCIe 4.0 SSDs offer two notable advantages over the previous versions; speed and power efficiency. NVMe SSDs can specifically take advantage of PCIe 4.0’s high-speed transfer rate. When used on PCIe 3.0, NVMe SSDs have a tendency to congest the lanes because PCIe 3.0’s bandwidth and transfer rate are insufficient to fully support NVMe devices. On the other hand, PCIe 4.0 provides a faster transfer speed and higher bandwidth for NVMe SSDs relieving much of the workload while at the same time consuming less power.
Based on an actual test, a PCIe 4.0 SSDs can achieve sequential read speeds of up to 6,900 MB/s and write speeds of up to 4,200 MB/s. Expectedly, PCIe 3.0 SSD’s read and write speeds are approximately half of that of PCIe 4.0 SSD at 3,350 MB/s and 3,040 MB/s respectively. PCIe 4.0 SSD also proves to be more power efficient than PCIe 3.0 SSD. With one watt of electricity, a PCIe 4.0 SSD can read 276MB/s of data while a PCIe 3.0 SSD can only read 134MB/s of data with the same amount of electricity.
While consumers can barely notice the performance difference that PCIe 4.0 offers, data centers and other industries that process large volumes of data can clearly distinguish the performance boost and the reduction in electricity consumption using the new PCIe standard. PCIe 4.0 SSD also brings forth a significant improvement on applications with dense workloads like artificial intelligence, cloud computing, and machine learning.
The increasing demand for faster data processing of data-intensive applications, the need for faster internet speed, and the growing number of IoT devices all require a more advanced and faster transfer interface. Newer and faster storage solutions like NVMe SSD are also taking over the slower SATA-based SSDs and are requiring faster PCIe interface for optimum performance. PCIe 4.0 is currently the fastest PCIe interface that can cater to today’s need for instantaneous data processing and PCIe 4.0 SSDs are one of the devices that can greatly benefit from PCIe 4.0’s powerful specifications.
PCIe 4.0 motherboards along with PCIe 4.0 SSDs are currently the best option for industries with large-scale data processing but it won’t be long before they reach the consumer market as more applications are requiring the low-latency and extremely fast read/write speeds of PCIe 4.0 SSDs.
 Alsop, Thomas. “HDDs and SSDs: global shipments 2015-2021”. https://www.statista.com/statistics/285474/hdds-and-ssds-in-pcs-global-shipments-2012-2017/ March 2, 2020 Accessed June 12, 2021
 PCIe 4.0 (Ultimate Guide To Understanding PCI Express Gen 4). December 28, 2020. https://premioinc.com/blogs/blog/pcie-4-0-pci-express-gen-4 Accessed June 12, 2021