Which of the three high-speed interfaces is faster？
In today's world where computer and storage systems continuously pursue higher data throughput, interface and bus technologies have become critical bottlenecks in performance. DisplayPort, PCIe 5.0, and SAS each serve the three major domains of display, internal expansion, and storage. Although their application scenarios differ, they all share a core pursuit of higher bandwidth, lower latency, and improved signal integrity. This article will introduce the technologies represented by these three keywords and compare their differing approaches to bandwidth design.
1. DisplayPort Bandwidth: Designed for High Resolution and High Refresh Rates
DisplayPort (DP) is a digital display interface standard promoted by the Video Electronics Standards Association (VESA), widely used in monitors, graphics cards, and laptops.
Bandwidth Evolution:
DP 1.4 uses a 4-lane HBR3 mode, with 8.1 Gbps per lane, delivering a raw total bandwidth of approximately 32.4 Gbps and an effective data bandwidth of about 25.92 Gbps (due to 8b/10b encoding overhead).
DP 2.0 / 2.1 introduces the UHBR (Ultra-High Bit Rate) mechanism: UHBR 10, UHBR 13.5, and UHBR 20 correspond to 10 Gbps, 13.5 Gbps, and 20 Gbps per lane, respectively. With four lanes, UHBR 20 achieves a raw bandwidth as high as 80 Gbps, with an effective data bandwidth reaching 77.37 Gbps (using 128b/132b encoding, significantly improving efficiency).
Practical Implications:
This high bandwidth supports 16K displays (@60Hz) or dual 8K displays (@120Hz) without requiring Display Stream Compression (DSC). DP 2.1 also integrates physical layer compatibility with USB4 V2 and Thunderbolt 5, enabling shared channels for video and data transmission.
2. PCIe 5.0 Specification: The Hub for General-Purpose Internal Interconnects
PCI Express (PCIe) serves as the primary communication backbone between CPUs and GPUs, SSDs, network cards, and nearly all high-performance expansion cards. PCIe 5.0 was released in 2019, doubling the bandwidth compared to PCIe 4.0.
Core Parameters:
Per-lane unidirectional rate: 32 GT/s (gigatransfers per second)
Encoding method: 128b/130b, effective data rate approximately 31.5 Gbps
Typical configuration: x16 slot provides 63 GB/s bidirectional total bandwidth (approximately 63 GB/s unidirectional due to full-duplex operation)
Note: The term "bandwidth" is often used differently—PCIe 5.0 x16 unidirectional bandwidth is approximately 64 GB/s (32 GT/s × 16 × (128/130) / 8 ≈ 63.0 GB/s).
Application Value:
Supports Gen5 NVMe SSDs with sequential read speeds exceeding 14 GB/s.
Significantly reduces memory access latency between GPUs and CPUs, as well as RDMA network card delays.
Provides the physical foundation for CXL (Compute Express Link), enabling memory pooling and heterogeneous computing.
PCIe 5.0 is not merely a doubling of bandwidth; it also includes improvements in signal integrity, connector optimization, and backward compatibility with earlier PCIe versions.
III. SAS Interface: The King of Reliability and Scalability for Enterprise Storage
SAS (Serial Attached SCSI) is a high-performance storage interface designed for enterprise hard drives, tape libraries, and SSDs, complementing consumer-grade SATA. Current major versions include SAS-3 (12 Gbps) and SAS-4 (22.5 Gbps), while SAS-5 (24G) is already in the specification development phase.
Key Metrics:
SAS-3 (12G): 1.2 GB/s per lane (raw 12 Gbps, using 8b/10b encoding, effective 1.2 GB/s).
SAS-4 (22.5G): Effective ~2.25 GB/s (raw 22.5 Gbps, still using 8b/10b encoding).
Multi-lane wide ports (e.g., 4x wide port) can linearly scale bandwidth up to 9 GB/s (SAS-4 ×4).
Differences from PCIe SSDs:
SAS emphasizes dual-port design for high availability (failover via secondary port when one link fails), multi-initiator support (multiple hosts sharing storage), long-distance transmission (via copper or fiber), and end-to-end SCSI command sets, making it ideal for SAN or DAS environments. In contrast, NVMe over PCIe offers higher performance but traditionally lacks multi-host failover capabilities (though NVMe over Fabric is closing this gap).
IV. Comparison from a Bandwidth Perspective
| Feature | DisplayPort 2.1 | PCIe 5.0 x16 | SAS-4 (Single Lane) |
| Raw signaling rate | 20 Gbps/lane | 32 GT/s | 22.5 Gbps |
| Encoding efficiency | 128b/132b (~97%) | 128b/130b (~98.5%) | 8b/10b (80%) |
| Effective unidirectional bandwidth | ~19.3 Gbps/lane ×4 | ~63 GB/s (total bidirectional) | ~2.25 GB/s |
| Typical use case | GPU → Monitor | CPU ↔ SSD/GPU | Disk enclosure ↔ RAID card |
| Cable length | 1–2 meters (passive) | 0.3–1 meter (board-level/backplane) | Up to 10 meters (active cable) | In terms of bandwidth, PCIe 5.0 significantly outperforms SAS, but the two are not substitutes—PCIe handles general-purpose data transfer at the board level, while SAS addresses shared access, redundancy, and long-distance connections across multiple drives. DisplayPort's bandwidth increase is entirely dedicated to uncompressed, low-latency pixel transmission, which demands extremely high real-time performance.
V. Future Integration Trends
PCIe 6.0 / 7.0: Utilizes PAM4 modulation, with 6.0 reaching 64 GT/s and 7.0 expected to reach 128 GT/s. In the future, PCIe may also serve as external interconnection (via copper cables or optical interconnection).
DisplayPort over USB-C: DP bandwidth is dynamically shared with USB4, enabling a single cable to simultaneously transmit video, data, and power supply.
SAS and NVMe Mixed Use: The new generation of SAS controllers supports the NVMe protocol. Enterprises can mix SAS hard drives and NVMe SSDs on the same backplane and achieve unified management through PCIe switching. Summary
The DisplayPort bandwidth, PCIe 5.0 specification, and SAS interface respectively represent the latest technologies in the three fields of display terminals, system buses, and storage interconnection. Their common point is that they all experienced a doubling of bandwidth in recent years. The differences lie in encoding efficiency, topology structure, reliability requirements, and usage distance. Understanding the design philosophy of these three technologies can help make the right interface selection when building workstations, servers, or audio-visual systems.
In the future, as CXL, USB4, and optical interconnection technologies mature, these three technology lines will accelerate their integration. However, for specific scenarios such as high-fidelity video, high-density computing, and enterprise storage, their distinct features will still remain.
Post time: May-27-2026
