The AdvancedTCA community is nearing completion of a fairly major enhancement to the core ATCA standard. This new specification is known as “PICMG 3.7” or “ATCA Extensions.” It expands the packaging definitions to include dual sided shelves, where ATCA boards can plug into either the front of the back of a double-deep rack and interconnect through a single or dual backplanes. Both vertical and horizontal board orientations are defined. In addition to this, the Extensions specification also allows for something called Extended Transition Module (ETM) that is essentially a front board-sized circuit board that connects to a front board via Zone 3, much like a standard Rear Transition Module.
These new mechanical configurations significantly expand the flexibility and versatility of ATCA. The double-deep configurations can make better use of available rack space when compared to single-deep systems.
There are many variations of interconnects allowed, but Figure 1 below gives a general idea of the concept.
Importantly, PICMG 3.7 provides a much more detailed definition of, and support for, double wide modules than the original specification. These can support multiple processors, bigger heatsinks, cheaper full height memory modules, and multiple disk drives on a single assembly if desired. PICMG 3.7 also defines requirements for typical data center environments in addition to the telecom central office. Double wide modules can support up to 800W of power dissipation if the shelf is built for that. AC as well as traditional -48VDC power environments are also supported. PICMG 3.7 also provides a much more rigorous definition of the thermal environment within a shelf and provides useful guidance for those designing high power systems.