In the DC-MHS modular server standard, the host processor module (HPM) is the server board: the PCB that holds the CPU, memory and the connectors that join it to the rest of the system. Two OCP specifications define its shape. M-FLW covers the full-width HPM, and M-DNO covers partial-width, density-optimized HPMs. This guide explains how they differ and which connectors each one specifies.
In short:
- The HPM is the motherboard-class board. The specifications define its outline, mounting, connectors and power zones, and leave the CPU, memory, voltage regulators and cooling to the designer.
- M-FLW is the full-width form factor (Type 1). M-DNO covers half-width and three-quarter-width boards.
- Both use SFF-TA-1033 for risers and require the cabled M-XIO connector family for high-speed I/O.
- Both assume 12 V DC power.
The specification versions below are release candidates (M-FLW v1.0 RC5 and M-DNO v1.1 RC2), so check the current release before designing to them. For the overall standard see DC-MHS and M-XIO.
What an HPM Is
The M-FLW specification calls the HPM a PCB or PCBA form factor, also called a motherboard or board. It sets the board outline, the mounting holes, where connectors sit and how much power each zone can supply. It does not define the compute core: CPU, memory, voltage regulators, thermal solutions and cooling connections are out of scope.
M-FLW: Full Width
M-FLW covers the full-width HPM, which it calls Type 1. It targets 1U and 2U chassis in racks that meet the 19-inch EIA-310-E standard. The specification says it can also fit larger 21-inch racks, but treats the 21-inch example as informative only.
Key points from the specification:
- Near-side I/O: six Near IO positions for risers, using SFF-TA-1033 connectors. A board does not have to populate all six, but using as many as possible is recommended.
- Other modules: OCP NIC 3.0 (R3) and DC-SCM (R2) use SFF-TA-1002. See our SFF-TA-1002 guide.
- Far-side high-speed I/O: low-profile SFF-TA-1016 (MCIO) or SFF-TA-1026.
- Required connectors: two control panel connectors, M-CRPS power connectors and six 2x6+12 PICPWR locations.
- Power: 12 V DC input. Zone ratings are M-CRPS ingress up to 3,200 W, PICPWR egress up to 864 W, near-side riser egress up to 252 W per Near IO connector, DC-SCM up to 50 W, and OCP NIC plus a platform custom zone up to 160 W.
- Mechanical: six required mounting holes, a datum hole and a slotted hole for alignment, and a board thickness cap of 3.18 mm nominal.
M-DNO: Partial Width, Density Optimized
M-DNO defines HPMs narrower than full width, for designs that put several nodes in one chassis. It covers:
- Half width: 210 mm wide, Types 2 and 3.
- Three-quarter width: 295 mm wide, Type 4.
Type 3 was completed in v1.1 with a 550 mm length. Type 1 is in M-FLW, and full-width and narrower-than-half-width boards are out of scope. The two specifications do not aim for interoperability with each other.
Other points from M-DNO:
- Connectors: DC-SCM 2.x is required at a fixed location. OCP NIC 3.0 is strongly recommended at a fixed location if implemented. Fixed riser locations use SFF-TA-1033 with 21 A power, with risers 1 and 2 on Types 2 and 3 and risers 1, 2 and 3 on Type 4.
- High-speed I/O: must be M-XIO compliant, meaning SFF-TA-1016, 1026 or 1033.
- Power: 12 V DC ingress and egress. PICPWR connectors are 2x6+12SB (864 W) or 2x3+6SB (486 W). Each riser location must receive at least 87 W, enough for one 75 W PCIe CEM card. The riser connector is rated 252 W, DC-SCM 50 W and OCP NIC 3.0 80 W.
- Chassis widths: multi-node chassis use a 443 mm inner width and monolithic chassis 431 mm, both in 19-inch racks.
- M-SDNO: builds on M-DNO and adds variable board outlines for 19-inch EIA-310 and 21-inch Open Rack V3 chassis.
Why the Connector List Matters
The HPM specifications fix where the connectors sit, which is what lets a riser, a NIC or a management module move between servers from different makers. For a supplier, that means the part has to match the standard's connector family, location and power rating, not only the electrical pinout.
Selection Checklist
- Which HPM type: M-FLW Type 1, or M-DNO Type 2, 3 or 4.
- Riser connector: SFF-TA-1033 with the power rating the type requires.
- High-speed I/O: an M-XIO compliant connector (MCIO, SFF-TA-1026 or 1033).
- Management and NIC modules: SFF-TA-1002 for DC-SCM and OCP NIC 3.0.
- Power connectors: M-CRPS and PICPWR sized for the zone ratings above.
- Mechanical fit: mounting holes, board thickness and height zones.
- Spec version: confirm the released version, not only the release candidate.
Frequently Asked Questions
What does HPM stand for? Host processor module.
What is the difference between M-FLW and M-DNO? M-FLW is the full-width form factor. M-DNO covers partial widths for density-optimized designs.
Does DC-MHS work in a 21-inch Open Rack? M-FLW treats 21-inch support as informative. M-SDNO adds board outlines for 21-inch Open Rack V3.
What voltage does an HPM use? 12 V DC.
Where to Go Next
Sources
- OCP M-FLW R1 v1.0 RC5: full-width HPM, connectors, mounting and power zones.
- OCP M-DNO R1 v1.1 RC2: partial-width HPM types, connectors and power.