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PCIe SSDs—solid state drives that connect to computer motherboards using the Peripheral Component Interconnect Express standard, or PCIe—offer improved speeds over drives connected using traditional serial AT attachment (SATA) interfaces. These connection standards allow computers to make the most of the faster performance SSDs offer over mechanical hard drives. Here’s a closer look at how they work.
What is PCIe?
PCIe is a widely used standard that allows peripherals and components—including solid state drives—to communicate with a computer’s central processing unit (CPU). The latest version, PCIe 6.0, offers the best performance yet. Though it is not widely available, it promises to meet the increased demand for faster, more efficient data storage and transfer by reducing latency, doubling speed and bandwidth, and reducing boot and processing times.
High-performance motherboards are built with PCIe slots that can be used to add peripheral devices, including SSDs. PCIe slots come in different physical configurations based upon the number of “lanes” they provide for data to travel over:
- PCIe x1 is the smallest PCIe slot. It uses a single lane for data travel and is typically used for USB expansion cards, basic network adapters, and other cards.
- PCIe x4 uses four lanes and is often used for high-speed network adapters and SSD expansion cards. They can fit into PCIe x16 slots.
- PCIe x8 uses eight lanes and are typically used for graphics cards or SSD expansion cards. They can also fit into PCIe x16 slots.
- PCIe x16 are the largest slots, with 16 lanes, and are used for high bandwidth peripherals.
PCIe slots are made up of two facets, mechanical cards and electrical (lanes). In practice, this means a slot might be x16 mechanical but only x8 electrical. Even though it can physically hold 16 PCIe cards, it can only support eight lanes, resulting in reduced performance.
PCI vs PCIe
PCI is a much older standard that predated PCIe. PCI slots are generally longer than PCIe slots, but run at a much slower speed. In the PCI standard, all devices share the same parallel bus, while the PCIe internal architecture more closely resembles a local area network with each link connected to a central switch in the computer.
Even the slowest PCIe version is significantly faster than the maximum PCI bandwidth of 532 MBps. Besides speed, PCIe also offers advanced error detection and reporting and the ability to hot-swap devices so that they can be inserted and detected without the need to reboot the system.
PCIe vs. SATA Solid State Drives
When shopping for SSDs, the choice often comes down to PCIe vs SATA. The key benefit of PCIe is the huge performance boost it provides over SATA drives—especially with the advent of non-volatile memory express (NVMe) PCIe solid state drives, which are even faster. NVMe is a host-controller interface specification that uses the PCIe bus to connect SSDs to computers, boosting speed and reducing latency.
SATA drives cost less than PCIe SSDs, and offer some other advantages for certain use cases:
- Compatibility: Because SATA is older, it is much more common. SATA SSDs are likely to be compatible with older systems than PCIe SSDs.
- Efficiency: SATA is also less sophisticated, which means the energy consumption is likely to be lower. This can have implications for laptop battery life and in large data centers where power and cooling costs can be considerable.
- AHCI: SATA SSDs can be hot-swapped in and out of a system as long as the system is using the advanced host controller interface (AHCI), which can often be enabled in the system BIOS. PCIe SSDs can be hot-swapped by default.
Learn more about PCIe NVMe vs. other SSDs.
PCIe SSD Form Factors
PCIe SSDs come in a variety of shapes and sizes, including the following:
- Add-in or Expansion Cards. The most common form of PCIe SSDs, these can be inserted into motherboard PCIe expansion slots and offer high storage capacities and the ability to support multiple flash memory modules.
- M.2. This compact, versatile format has gained popularity in recent years. These cards are about the size of a stick of chewing gum and connect directly to the motherboard via an M.2 slot, reducing cable usage and clutter in the hardware environment. M.2 cards are often found in laptops and smaller desktop models. M.2 SSD cards can support various PCIe generations.
- U.2. This 2.5-inch card was previously known as SFF-8639 and is compatible with both PCIe and SATA interfaces. U.2 offers larger storage capacity than M.2 drives and is used in enterprise storage systems and high-end desktops, among other applications requiring high performance.
- Full Height/Half Length (FHHL). This format has reduced height and length to fit into areas where larger cards won’t fit, such as blade servers, compact workstations, and embedded systems.
PCIe Versions
Released in January 2022, but not yet widely available, PCIe 6.0 sets a new benchmark for data transfer rates—64 GT/s per lane, double the capacity of PCIe 5.0. The jump in speed means PCIe 6.0 will be instrumental in the development of technology for autonomous vehicles, edge computing, and the advanced machine learning algorithms integral to countless applications, systems, and processes.
PCIe 6.0 maximizes data throughput by using pulse-amplitude modulation (PAM4) encoding, allowing for increased data density and efficiency. Other benefits include:
- Improved Scalability. PCIe 6.0 supports up to 256 lanes, greatly increasing opportunities for scaling even in massively data-intense environments.
- Enhanced Power Efficiency. This version of PCIe includes new power-saving features, including L1 substates, which add energy conservation during idle periods. Portable devices especially benefit from this improvement.
- Backward Compatibility. PCIe 6.0 is backward compatible with prior generations, improving integration with existing systems.
- Forward Error Correction. These algorithms can detect and actually correct transmission errors.
- High-Speed Interconnectivity. The higher bandwidth available with PCIe 6.0 improves interconnectivity between SSDs, GPUs, NICs, and many other devices.
Though not as fast as 6.0, PCIe 5.0 is significantly more robust in terms of data transfer speeds than prior generations. With a bandwidth of 32 GT/s per lane, it effectively doubles the throughput compared to PCIe 4.0 and PCIe 3.0, which are both still in widespread use.
PCIe 5.0 offers significant technology advancements, supporting applications like real-time 8K video processing, complex artificial intelligence (AI) algorithms and immersive virtual reality (VR). It is frequently used in environments within data centers, scientific research facilities and other areas where high performance computing is required. Other benefits include.
- Backward Compatibility. PCIe 5.0 is backward compatible with prior PCIe versions.
- Power Efficiency. PCIe 5.0 uses L1 substates that can conserve power during idle periods, which is especially valuable for portable devices.
- Widespread Adoption. By now, PCIe 5.0 has been adopted across many industries, with major tech companies coming on board in the past few years.
PCIe 7.0 is expected to debut in 2025.
Learn more about PCIe 5.0.
Bottom Line: PCIe Solid State Drives
Solid state drives offer improved performance over more traditional mechanical hard disk drives, and those using the PCIe standard are faster than their counterparts that rely on the SATA standard. The latest PCIe SSDs that benefit from NVMe technology are even faster still. While that improved performance comes at a higher cost, and may require some trade-offs around compatibility and power efficiency, buyers looking to build or update systems with the fastest speeds available should take advantage of PCIe technology.
