Implementing PCIe Gen 4 Expansion

Print Friendly, PDF & Email
PCIe Gen 4

In this week’s Guest Post, Katie (Garrison) Rivera of One Stop Systems explores PCIe Gen 4, which is fast becoming the latest de facto standard for general purpose I/O of the modern computer system. 

PCIe Gen 4

Katie (Garrison) Rivera, Marketing Communications Manager, One Stop Systems

After a long run for PCI Express (PCIe) Gen 3, Gen 4 is fast becoming the latest de facto standard for general purpose I/O of the modern computer system. While the IBM Power 9 server has been shipping with PCIe Gen 4 for a few months and, according to Tom’s Hardware, the next evolution of PCIe motherboards will begin hitting the market en masse within the next 6 to 12 months.  PCIe 4.0 doubles the performance of PCIe 3.0, is 6 times faster than the original PCIe 1.0, and includes improvements in flexibility, scalability and lower-power due to concurrent improvement in modern integrated circuit design starting with 16nm fabrication technology. According to the PCI-SIG, “functional enhancements include extended tags and credits for service devices, reduced system latency, lane margining, superior RAS capabilities, scalability for added lanes and bandwidth, as well as improved I/O virtualization and platform integration”. With PCIe bandwidth doubling, Gen 4 will sport single lane bandwidth of 16Gb/s and x16 bandwidth up to 256 Gb/s with many innovations on the horizon.

One of the largest innovations outside of CPU manufacturers integrating PCIe Gen 4 into their processors is PCIe over cable implementations. PCIe external cabling allows PCIe to run at full performance over a cable for bus extension, expansion, high-availability fail-over, or networking configurations. PCIe over cable provides full software transparency for driverless bus extension or expansion applications. The ability to run PCIe over cable at full performance with complete software transparency has opened up a range of new application possibilities over the past decade for CPU to I/O system re-partitioning with expansion systems uniquely situated to take advantage of the new PCIe Gen 4 bandwidth soon available on servers.

After a long run for PCI Express (PCIe) Gen 3, Gen 4 is fast becoming the latest de facto standard for general purpose I/O of the modern computer system.

In the early years of PCIe Gen 4 there will be relatively few Gen 4 slots available on servers and thousands of Gen 2 and Gen 3 add-in boards available in the market. Most enterprises have made huge investments in these Gen 2 and Gen 3 peripherals.  While bandwidth hungry, high-performance computing products such as NVMe SSDs, GPUs and FPGAs may be quick to adopt Gen 4 in the first year, it will likely take years for most PCIe peripherals to make the leap to Gen 4 because the bandwidth is simply not needed for every peripheral. PCIe Gen 4 expansion products allow customers to plug multiple Gen 1, Gen 2 or Gen 3 peripherals into a single PCIe Gen 4 slot using a low-cost, low-profile Gen 4 cable host interface board (HIB).  The HIB connects to a standard PCIe cable then to one or more expansion chassis with a PCIe switch which aggregates the bandwidth of the older generation cards into the latest generation Gen 4 slot. Additional benefits abound since the peripherals in the expansion chassis can exchange DMA peer-to-peer transactions locally in the expansion chassis with minimal impact to host resources.

One Stop Systems (OSS) has consistently been first to market with each new generation of PCIe cable expansion products. Since 2005, OSS has designed and manufactured PCIe Gen 1 cable adapters, expansion systems and flash storage arrays ranging from one to 32 slots. With each new generation, OSS has released new cable adapters and expansion systems to keep up with the demands of the market and Gen 4 is no exception. The first OSS PCIe Gen 4 cable adapter, the HIB616, fits in a PCIe 4.0 x16 half-length, half-height server slot and features four SFF-8644 cable connectors, the same used for the latest 4x mini-SAS HD standard.  The flexible SFF-8644 connectors on the HIB616 support standard or cable management interface (CMI) compliant copper cables up to 5m as well as fiber optic cables up to 100m in length so PCIe compliant expansion systems can be installed adjacent to the Gen 4 server as an expansion system or across the data center. By having four x4 cables forming a x16 Gen 4 link, additional bifurcation options are possible with the HIB616, such as 2 x8 and 4 x4 links to multiple devices or expansion systems. This flexibility allows for the highest speed PCIe system-to-system and rack-to-rack interconnects in data centers, airborne installations and OEM applications with bandwidth up to 256 Gb/s and latency of less than 150ns.

PCIe Gen 4 is finally here and OSS helps all customers in HPC, instrumentation, military, media and entertainment markets take full advantage of the feature and bandwidth enhancements it brings. Servers available from major OEMs, such as IBM, currently provide Gen 4 slots for the newest OSS Gen 4 cable adapter with additional Gen 4 servers and PCIe switches on the horizon. The early years of Gen 4 benefit tremendously from PCIe expansion systems because of the pervasive use of Gen 3 devices that can be aggregated to a Gen 4 slot in a server thereby taking advantage of the additional bandwidth.

This guest article was submitted by Katie (Garrison) Rivera, marketing communications manager at One Stop Systems.