Spansion's move into using flash to replace DRAM in servers comes from the confluence of a number of trends: flash processes matching DRAM processes; server farms using too much energy; packaging allowing multi-die stacking.

"Flash has crossed over with DRAM as the industry driver and in cost per bit, cell-size per bit and the use of more aggressive processes," John Nation, Spansion's director of corporate marketing told Electronics Weekly.

Servers use DRAM for the initial access because hard discs are too slow. NOR flash, of the type Spansion is proposing to replace DRAM in servers, is, of course, a lot slower than DRAM. Maybe 3X slower.

But Spansion has come up with some software from Virident Systems which can all but reduce this speed deficit when used in servers. "The Virident software brings it up to pretty much DRAM access times," said Nation.

Apart from speed, the other disadvantage of NOR flash ever becoming a DRAM replacement is the cell size of NOR which is so much bigger than a DRAM cell.

"A DRAM cell is a single level cell, a Mirrobit NOR cell is a multi-level cell storing two bits per cell", said Nation. This brings the bit-per-cell size pretty much equivalent between Mirrobit NOR and DRAM.

Why not use NAND? "Because the NAND access time is so much slower - about 25 microseconds", replied Nation.

Having got over the intrinsic disadvantages of NOR flash as a DRAM replacement, the advantages are quite compelling: "At the device level the energy consumption is eight times less", said Nation.

That means that eight NOR die in a stacked package could use the same power as a single DRAM die while delivering eight times the density. That's a big selling point.

Spansion and Virident say the memory subsystem can use four times more memory without increasing power consumption, or the same amount of memory with a quarter of the power.

So server farms can get the same capacity from one server using their NOR-based memory as four servers using DRAM.

With servers taking 128GBytes of DRAM each, and the installation rate of servers growing exponentially, and the massive effect of the Green movement persuading people to save power, Spansion reckons it is on to a big winner with its NOR-based server memory which it calls EcoRAM.

See also: Mannerisms, the blog of David Manners. Updated twice daily, it's the distinctive, entertaining, authoritative and never dull commentary on the semiconductor industry, from someone who knows. Sign up for the Mannerisms eNewsletter.