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Connector and Cable differences: SAS-3 vs. SAS-4

24G SAS » Articles

By: David Einhorn, SCSI Trade Association Board of Directors; Business Development Manager, North America, Amphenol Corp., June 14, 2022

This blog post examines the differences between SAS-3 and SAS-4 connectors and cables. With the new generation of SAS, we see multiple upgrades and improvements.

Drive connector
[Note: 24G SAS uses the SAS-4 physical layer, which operates at a baud rate of 22.5Gb/s.]

The 29-position receptacle and plug connectors used in SAS-4 feature: hot-plugging, blind-mating, connector misalignment correction, and a PCB retention mechanism for robust SMT attachment. The connectors are SATA compliant and available across many suppliers in range of vertical and right-angle configurations. Typical applications are consistent with previous generations of server and storage equipment, HDDs, HDD carriers, and SSDs.

To fulfill the needs of next-generation servers, several improvements have been implemented. Raw materials have been upgraded, housing designs and terminal geometries have been modified to meet signal integrity requirements at 24G SAS speeds while maintaining the footprint of existing SAS-3 for easy upgrades.

  • Compliant to SFF8681 specification
  • Footprint backward compatible to 3Gb/s, 6Gb/s, and 12G SAS connectors
  • Staggered contact lengths for hot plugging applications
  • Receptacles are available in SMT, through-hole and hybrid PCB attach methods
  • Header is available in right angle and vertical orientation
  • Supports both SAS and SATA drives

Ultimately, the goal was to design a connector with the mechanical and electrical reliability which has been part of every previous SAS generation and improve the signal integrity to meet the 24G SAS need while maintaining backward compatibility.

Drive cable assembly
SAS-4 cables for next-generation servers perform to 24G SAS speeds with a significant size and density improvement from previous generations. An 8x SlimSAS consumes the same area as a 4x MiniSAS HD. From a construction standpoint, SlimSAS series plug connectors include an anti-skew feature for misalignment correction. An optimized raw cable structure and upgraded cable manufacturing process enables the enhanced signal integrity performance requirements of SAS-4. Additionally, the plug connector internal components have been optimized to control and stabilize the impedance. The connectors are compliant with SFF-8654 and meet a wide range of straight, right-angle, left-side and right-side exit configurations to solve most mechanical/dimensional constraints.

  • Compliant to SFF-8654 specification
  • Supports various plug connector types: straight, right angle, left-side exit, and right-side exit
  • Anti-skew feature is optional for special applications
  • Pull-tab is available for all type connectors
  • Anti-reverse right angle plug connector is available for supporting special applications
  • Metal latch adds robustness and improves on previous generations (MiniSAS HD)
  • Supports SAS, PCIe, UPI1.0, NVM Express® and NVLink® 25G applications
  • Supports 4x, 6x, 8x, and 12x configurations

The industry set out to design a high-performance cable assembly with the mechanical and electrical reliability which improves upon every previous SAS generation and improves the signal integrity to meet the SAS-4 requirements. The standards based SlimSAS product lines have been proven to reliably meet or exceed the storage industry needs.