If you heard a thump Monday, that was the cost of memory crashing.

What cost maybe five grand last week can now be had for, oh, $1,500.

See, Monday was when ex-AMD CTO Fred Weber’s stealth start-up, MetaRAM, came out of hiding sporting an attention-grabbing way to cut the price of a computer system outfitted with four quad processors and 256GB of main memory from $500,000 to below $50,000.

Memory is of course the most expensive part of high-end systems.

MetaRam’s secret is a memory chipset thought up by its co-founder ex-Nvidia/Rambus exec Suresh Rajan – and sorcery, of course.

The chipset, which sits between the memory controller and the DRAM, can make four one-gigabit DDR2 SDRAMs think they’re one big 4Gb DDR2 MetaSDRAM, something that doesn’t even exist in real life.

It’s a kind of applied virtualization that Fred says closes the “memory capacity gap” between Moore’s Law-impelled microprocessors – whose capacity doubles every 18 months – and laggard memory – which doubles only every 36 months, making it a major bottleneck in computing.

By doubling or quadrupling the memory capacity of existing Intel and AMD systems, MetaRAM claims to have accelerated memory development two-four years – all without requiring any hardware or software changes by the systems makers.

It’s pretty easy to grasp that using 1Gb DRAMs is cheaper than using 2Gb DRAMs and MetaRAM’s WakeOnUse technology keeps the widgetry on a strict 2.5W-maximum power budget. DRAMs sleep until they’re used.

Fred has a lovely overhead explaining how one 2P system can be better than two 2P systems and offer 100% CPU utilization versus 50% while saving 34% on power and 50% on space. The trick is in using 128GB DDR2 MetaSDRAM rather than two sets of 64GB DDR SDRAM.

MetaRAM’s arrival is timely, Fred says. All the sexy, in-demand, compute-intensive widgetry are memory eaters: multi-core CPUs, 64-chip computing, parallel applications, Web 2.0, virtualization and the yen to run in-memory databases.

Roughly 20% of the servers that ship, he says, could use his drop-in solution, which only works with DD2 registered DIMMs, not those newfangled fully buffered DIMMs that Intel has been pushing, the stuff that has met with mixed industry reaction. Fred’s company’s working on a DDR3 generation for next year.

MetaRAM and its systems friends – initially Colfax International, Appro, Rackable and Verari – have in mind aerospace and automotive, financial services, digital content creation and rendering, oil and gas exploration and semiconductor design and simulation.

The 180nm MetaRAM chipset worked on its first pass through manufacturing – a fact Fred lays to having a small team of eight “craftsmen,” the pick of the litter working on a “manageable problem.”

As a result the dingus is in full production for 2-rack 8GB DIMMS at speeds of up to 667MT/s. It runs $200 each in quantity.

A 16GB model, which could produce systems with a terabyte of main memory, is qualified for production and priced at $450 in quantity, but Fred was coy about when it would be available.

Hynix Semiconductor has packaged the chipset up in an 8GB MetaSDRAM R-DIMM for engineering samples. Smart Modular Technologies has qualification samples for $1,500.

Colfax is already out with MetaRAM-bearing systems.

MetaRAM got to where it is on $20 million from Sun’s three founders, among others.

Andy Bechtolsheim, a boy who has a Midas touch – he was after all Google’s initial investor – well, he kicked in seed money and then Bill Joy, a partner at Kleiner, Perkins, and Vinod Khosla’s VC fund came in along with Intel Capital and Storm Ventures.

Joy and ex-AMD president and COO Atiq Raza are on the board.

MetaDRAM has 50 patents pending.