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Since its launch in January 2006, the only thing that has been publicly known about former AMD CTO Fred Weber's new venture is its name: MetaRAM. Clearly, the stealth-mode company was working on something to do with RAM, but what? As of today, MetaRAM is finally ready to talk about its technology, and it appears to be a pretty solid evolutionary step for the tried-and-true SDRAM DIMM module. In short, MetaRAM's technology enables DIMM capacity increases of two or four times, so that a single DDR2 MetaSDRAM DIMM can hold 4GB or 8GB of memory while still being a drop-in replacement for a normal DIMM.
Because MetaRAM's high-capacity DIMMs look to an Intel or AMD system like normal DDR2 DIMMs, the company expects to see servers with memory configurations that would normally require expensive custom hardware to become significantly cheaper. One of MetaRAM's channel partners will soon announce a server with 256GB of main memory for under $50,000, with 500GB boxes on tap for a higher price points
I'm tempted to suggest that "500GB of memory oughta be enough for anybody," but MetaRAM is looking to virtualization and enterprise databases as application domains that provide a rationale for putting that much memory in a single server. MetaRAM claims that its own research indicates that 80 percent of enterprise server databases are under 500GB in size, and if this is true, then hosting those databases entirely in main memory could get a lot cheaper after today.
MetaRAM is a fabless semiconductor company, and its manufacturing partners are Hynix and SMART Modular. Both chipmakers are currently sampling 8GB DDR2 DIMMs, and MetaRAM expects to see servers and workstations that include the technology available from Rackable and launch partners later this quarter.
How it works
MetaRAM uses a 3D chip stacking technology to cram extra SDRAM chips onto the DIMM, with the result that each DIMM is actually two or four DIMMs worth of memory. Also on the DIMM is a pair of custom chips that are the secret sauce that makes MetaRAM work. This MetaRAM chipset sits in between the system's main memory controller and the on-DIMM DRAMs, routing reads and writes to the appropriate DRAM and hiding its own presence.
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"We had to make our chip look like a DRAM to the memory controller, and like a memory controller to the DRAMs," said Suresh Rajan, the MetaRAM co-founder whom I talked to about the company's technology. This memory traffic routing messes with the DDR2 DRAM timings quite a bit, so the MetaRAM chipset's dynamic command scheduling circuitry ends up doing a kind of "out-of-order execution" with the flow of reads and writes so that the DIMM can operate at a full 667MHz without any glitches.
A MetaRAM DIMM
Rajan claims that in order to squeeze its chipset into the standard DIMM power and thermal envelope, the company had to do a fully custom circuit design. "Ever single cell in the chip was hand-placed and hand-routed to make sure that the clocking fits with existing systems," said Rajan.
Also important in enabling MetaRAM to meet its strict power budget is the company's WakeOnUse technology, which works as follows: a MetaSDRAM DIMM tries to keep all of its on-board DRAMs asleep if possible, and since the MetaRAM chipset is constantly directing memory traffic, it has a good idea of where the next reads and writes will come from and which SDRAMs it should wake up. This dynamic power optimization, where SDRAMs are only awakened if they're about to be used, is key for keeping a MetaSDRAM DIMM within normal DIMM constraints.
I asked Rajan to compare and contrast MetaRAM with FB-DIMM in terms of power draw, and he told me that the typical FB-DIMM's AMB draws 5 to 7 watts. The MetaRAM chipset, in contrast, draws only 2.5 watts on the high end, and the power draw scales linearly with usage.
Ultimately, MetaRAM looks like a solid replacement for FB-DIMM. Sure, you're stuck with DDR2's bandwidth, but as a consolation prize you get a ton of extra capacity with the same power envelope and interface as regular DDR2 SDRAM. It's likely that a serial, packet-based memory protocol (a la RDRAM or FB-DIMM) is still in our future, but MetaRAM looks poised to tide us over nicely until that future arrives.
