What is Server System Infrastructure?

Server System Infrastructure (SSI) is a set of specifications created to define commonly used server components. The SSI community develops specifications that standardize the critical server elements as well as interfaces between the elements such as boards, chassis and power supplies. This helps in developing common server hardware which in turn simplifies building of server solutions.

The specifications include the standards for all the building blocks of a server system and have all the details of the computer modules, system management, mezzanine cards, interconnections and more. The individual details specify required, recommended, and optional physical and electrical characteristics of:

  • Power supplies
  • Electronic bays (Chassis)
  • Chassis
  • Micro servers
  • Power control and management
  • Rack mount server chassis
  • Redundant power supplies

What is Server System Infrastructure

Figure 1: SSI specification creation to product creation – Image Credit

SSI guidelines on power supplies for servers and workstation

The standard requirements for the power supplies specify typical form factors, support for rack mounting, redundant and non-redundant power supplies requirements, and more. The standards specify the required, recommended and optional voltage and current levels as well as protection against over current, over voltage and over temperature. Other specifications are for the connectors, cables, cooling and other parameters necessary for the proper functioning of the power supply.

The required specifications must be implemented for the design to meet the SSI guidelines whereas the recommended and optional are not required in meeting the SSI guidelines, they are often necessary in most servers systems.


Required specs are Standby outputs, grounding, AC line fuse, output connectors, AC line dropout, AC inlet connectors, AC inrush control, voltage regulation, dynamic loading, timing, over current, overvoltage, over temperature protection, etc.

Some examples of the required specifications are:

  • Protection circuit: An internal protection that shuts down its main outputs. The tripping should be reset by an AC cycle off or PSON HIGH.
  • Current limit: There are set current limits on the =3.3, +5 and +12 Volts outputs. The current should not exceed the set values; otherwise the power supply shuts down and latches off. The latching off is cleared by cycling the power or by toggling the PSON signal.
  • The -12 Volt and 5VSB volt outputs as well as all the other outputs should also be protected against over current conditions or short circuit conditions. This is meant to prevent further damage to the power supply arising from these conditions.


Recommended specs are Temperature Requirements, AC Line Transient Specification, On State – efficiency levels at different load states, Standby state- standby state efficiency for energy star specifications – at different standby currents.

  • Minimum and maximum temperatures within which the power supplies should operate
  • The airflow should be through the power supply and not pass over the exterior surfaces
  • Airflow of at least 14 CFM and the air to exit from the AC inlet face of the power supply
  • Power supplies are recommended to have variable speed fans.
  • Certain sound levels recommended at different fan speeds based on the temperature
  • Currents based on the wattage of the power supply


Server signal connector, Workstation power connector for high power graphics cards, efficiency level, Serial ATA Power Connector etc.

Benefits of SSI

The standards, which are supported by manufacturers, suppliers and server components community, deliver significant benefits to server industry and customers.

Ecosystem Benefits

The standards remove barriers and make it easy for new entrants into the server industry to innovate and produce compatible equipment. This reduces costs, and manufacturers do not have to re-invent some of the parts – they only need to follow regulations and be innovative.

  • Reduced manufacturing costs
  • Enabling innovation: since manufacturers are able to focus on improving the capabilities of their product.
  • Faster time-to-market: since most of the technology is already specified by the standards, companies have less work and able to deliver products to the market faster.
  • Reduced engineering costs: the power, software communications and the electrical and mechanical interconnects standards eliminate the need to work on new designs hence reducing manufacturing costs

Customer Benefits

  • Reduced operating and maintenance costs due to increased availability of cost competitive parts.
  • Guaranteed compliance
  • Increased choice and flexibility of server components
  • Reduced migration costs
  • Reduced acquisition costs
  • Increased competitive advantage: The standards eliminate vendor lock-in and IT departments are able to upgrade their systems using components from other vendors