I'd be curious to hear from anyone who has worked on embedded systems with relatively large amounts of directly-addressable RAM.
I'm discussing with a colleague/client an application that would work on a nominally 740GB data set. The nature of the data and the required processing is such that it's a "must-have" performance improvement to hold the entire data set in RAM rather than swapping in from some secondary storage mechanism. It's perfectly acceptable for the machine to take an entire week to cold-boot. It's not acceptable, once booted, for it to wait several seconds to page in data from a hard disk :)
Hence I would say my RAM requirement would be speced at 1TB of error-correcting RAM. The hardware interfaces I would require are gigabit Ethernet, SATA for the boot media, and a means for connecting to an ASIC that does all the real processing work. The interface for that latter is not yet defined, but would quite likely be PCI Express. All this suggests a PC-style architecture as the way to go.
I'm really not finding much (read: anything) in the way of monolithic computer modules that can address 1TB. I've found mention of server clusters that have that much in aggregate, but it's spread across several computers. OS support for such large RAM sizes also appears to be problematic, but I could work around this.
Is anyone else dealing with similar problems? This is strictly a theoretical investigation for me now - more of a feasibility review than anything else - but it's quite an intriguing project. Maybe the right approach is to build a massively parallel engine with identical modules handling manageable (8GB?) slices of the data set. However this would be very expensive in terms of power and additional support circuitry.