SlimSAS (SFF-8654) Cable Assemblies
SlimSAS is the connector most likely to be ordered correctly and wired wrong. It is compact, it is dense, and it carries two completely different protocols through an identical-looking shell — which means a cable that mates perfectly can still fail to bring a drive up. EPS builds SlimSAS assemblies to a defined endpoint pairing, protocol path and orientation, rather than to a part number that only describes the shape.
On this page
- What is SlimSAS (SFF-8654)?
- What does the SFF-8654 standard define?
- What does 16i mean on a SlimSAS cable?
- Does a SlimSAS connector tell you the protocol?
- What does a SlimSAS cable connect?
- What should you confirm before specifying a SlimSAS assembly?
- What SlimSAS assemblies does EPS build to specification?
- What information does EPS need to quote a SlimSAS cable?
- Frequently asked questions
What is SlimSAS (SFF-8654)?
SlimSAS is the industry name for SFF-8654, a compact, high-speed internal connector specification maintained by the SFF TA Technical Work Group under SNIA. Its formal title is the 0.6mm 4/8X Unshielded I/O Connector specification; everyone, including the standards documents themselves, uses the industry names. We do too.
It is used for both SAS and PCIe storage paths. Which one a given assembly carries is set by the host and the wiring, not by the connector.
You will also see this connector called Slimline SAS and Slim SAS. All three names refer to SFF-8654.
What does the SFF-8654 standard define?
SFF-8654 defines two configurations. The specification's own notation is 4X and 8X; the industry writes them 4i and 8i, where "i" denotes internal.
| Configuration | Spec notation | Industry name | Positions |
|---|---|---|---|
| 4-lane internal | 4X | 4i | 38-position |
| 8-lane internal | 8X | 8i | 74-position |
What does 16i mean on a SlimSAS cable?
SFF-8654 defines no 16-lane configuration. There is no 16X in the specification.
Parts are nevertheless sold as "SlimSAS 16i" for sixteen-lane assemblies, and the term is in wide industry use. It is vendor and industry nomenclature, not an SFF-8654 configuration — which is why we will not publish a position count for it. A number stated against a standard that does not define the variant would be a guess wearing a specification's clothes.
If you are specifying a sixteen-lane assembly, tell us the connector on each end and we will confirm the mechanical detail against the actual part rather than against SFF-8654. That is the only way to get it right, and it is why the distinction matters commercially rather than just pedantically.
Does a SlimSAS connector tell you the protocol?
This is the single most consequential fact about SlimSAS, and where most mis-specifications originate.
The same SlimSAS connector family carries SAS and PCIe paths depending on the host and the cable's internal wiring. The protocol is set by the host controller and the wiring inside the assembly — not by the connector shape. A SlimSAS cable that physically mates can still be wired for the wrong protocol, or the wrong direction.
A point worth being precise about: SFF-8654 identifies SAS and PCIe as applications. It does not state a per-lane rate, a "24G" designation, or a PCIe generation — those come from INCITS/T10 and PCI-SIG respectively, or from the manufacturer's own rating for a specific assembly. Anyone quoting you a generation off a connector name is quoting something the connector specification does not contain.
Pinout assignments are a separate matter again: SFF-8654 refers them to SFF-9400 and SFF-9402, and SFF-9402 defines protocol-specific pinouts and sideband assignments. A cable wired for one protocol is not interchangeable across protocols even where the connector is identical.
Wiring and orientation both vary. SlimSAS cables are built for specific roles: PCIe versus SAS, host-side versus target/device-side. Those are different cables that look the same.
What does a SlimSAS cable connect?
SlimSAS links host controllers — HBAs, RAID cards, motherboard SlimSAS ports — to drives, backplanes and adapters. The common topologies:
- Host SlimSAS to U.2 (SFF-8639) drives
- Host SlimSAS to Mini-SAS HD (SFF-8643) backplanes
- One 8i port split to two 4i connectors — a Y cable
- One 8i port split to two U.2 (SFF-8639) drives
A U.2 drive always needs separate power. This is not a "usually" — SFF-9402 defines the root-to-endpoint POWER pins as NO WIRE, and SFF-8639 carries its own dedicated power section. The data assembly does not deliver drive power, by design. Specify the power path as part of the harness.
What should you confirm before specifying a SlimSAS assembly?
These are the assumptions that break builds. Every one is a documented trap.
- SlimSAS (SFF-8654) and Mini-SAS HD (SFF-8643/8644) are not interchangeable. Different connectors; they must match on both ends. Physical similarity is not compatibility.
- Do not assume a SlimSAS cable carries PCIe. It may be wired for SAS. Verify the intended protocol.
- Host-side and target/device-side cables are not the same. Orientation and wiring differ.
- Generation and lane width are not implied by the connector. SFF-8654 states neither. Verify the rating from the assembly's own specification or the manufacturer — not from the shell, and not from the connector standard.
- "16i" is not an SFF-8654 configuration. The standard defines 4X and 8X only. Sixteen-lane parts exist under industry nomenclature; confirm them against the actual connector.
- Do not assume the host or backplane supports the intended path unless it is documented or validated on the bench.
What SlimSAS assemblies does EPS build to specification?
EPS manufactures SlimSAS assemblies to your specification in Acton, Massachusetts, from prototype through production — 10 units to 10,000-plus. Every assembly is QC tested.
You specify: cable length, conductor size (AWG), conductor colors, wire stranding type, and shielding — foil, braid, or a combination. Jacket material can be PVC, TPU, FEP or LSZH, selected against temperature rating, chemical resistance, and plenum, riser or outdoor rating. Termination is built to your requirement — overmolded boots, strain reliefs, latch and locking systems, custom contact configurations. Custom colors and labeling can be specified.
Three steps: engineering review, quote and approval, then manufacture and delivery. Lead time depends on the specification and the volume, and we confirm it with your quote rather than quoting a standard interval that would not survive contact with your build. Long-term supply agreements support programs that need continuity.
Looking for a stocked part rather than a custom build? See available SlimSAS parts at MicroSATACables.
What information does EPS need to quote a SlimSAS cable?
- What exact connector is on each end — SlimSAS 4i, 8i, 16i, U.2, Mini-SAS HD?
- Is the path PCIe/NVMe or SAS, and at what generation and lane width?
- Is the cable for host-side or target/device-side use?
- Is a Y cable required — 8i to two 4i, or 8i to two U.2?
- Does a connected drive need a separate power lead?
Frequently asked questions
What is SlimSAS?
SlimSAS (SFF-8654) is a compact, high-speed internal connector standard maintained by the SFF TA Technical Work Group under SNIA. It is the modern successor to Mini-SAS HD for dense internal cabling. It is also called Slimline SAS and Slim SAS.
What is the difference between SlimSAS 4i and 8i?
The number is the lane count and "i" denotes internal. SFF-8654 defines two configurations: 4X, written 4i in industry use, at 38 positions; and 8X, written 8i, at 74 positions.
Is there a SlimSAS 16i?
Not in the standard. SFF-8654 defines 4X and 8X only — there is no 16-lane configuration in the specification. Parts are sold as "SlimSAS 16i" and the term is in wide industry use, but it is vendor nomenclature rather than an SFF-8654 configuration. We confirm sixteen-lane assemblies against the actual connector rather than against the standard.
Is SlimSAS the same as Mini-SAS HD?
No. SlimSAS (SFF-8654) and Mini-SAS HD (SFF-8643/8644) are distinct connectors and are not interchangeable. They must match on both ends of the run.
What protocols does SlimSAS carry?
SFF-8654 identifies SAS and PCIe as applications. It does not state a per-lane rate or a PCIe generation — those come from INCITS/T10 and PCI-SIG, or from the manufacturer's rating for a specific assembly. Which protocol a given cable carries depends on the host and the internal wiring.
Does a SlimSAS connector tell me whether the path is PCIe or SAS?
No. The protocol is determined by the host controller and the cable's internal wiring, not the connector shape. Verify the intended path from the specification.
Are host-side and device-side SlimSAS cables interchangeable?
No. They are built for a specific direction; orientation and wiring differ.
Can a SlimSAS 8i port be split?
Yes. A Y cable splits one 8i host port to two 4i connectors, or to two U.2 (SFF-8639) drives, for multi-drive PCIe/NVMe or SAS paths.
Does a U.2 drive on a SlimSAS run need separate power?
Always. SFF-9402 defines the root-to-endpoint power pins as no wire, and SFF-8639 carries a dedicated power section. The data assembly does not deliver drive power. Specify the power path with the harness.
Can I tell the PCIe generation from the connector?
No, and SFF-8654 does not state one. Generation and lane rate come from the assembly's own specification or the manufacturer, not from the connector standard.
Is a SlimSAS cable wired for SAS usable on a PCIe path?
Not reliably. SFF-9402 defines protocol-specific pinouts and sideband assignments, so an assembly built for one protocol is not interchangeable with another even where the connector is identical.
Have a custom interconnect challenge that off-the-shelf parts won’t solve?
EPS engineers and manufactures precision cable assemblies, signal-conditioning AICs, and custom enclosures for OEM partners, in Acton, Massachusetts. Lead time is confirmed with your quote against the actual specification and volume.