Tuesday, July 11, 2006

Magnetoresistive RAM

Freescale has a neat new computer memory technology, MRAM, that uses magnetism to store the data.  It's a little like old-fashioned magnetic core memory, but with the pieces laid down photographically instead of weaving wires through magnetic rings.

MRAM's claims to fame are that (1) the data is preserved even when the power goes off, and (2) it does not wear out when written.  Flash memory does #1, but fails miserably at #2, inevitably corrupting the data when it is written too many times. 

MR2A16A parameters
Parameter Value
Capacity 4 Mib (512 kiB)
Organization 256 ki × 16 bits
Max. ambient magnetic field 1.5 mT = 15 gauss
Operating temperature 0 – 70 °C
Power @ 3.3 V
155 mA
12 mA
Cycle time 35 ns (28 MHz)

The tolerance to ambient magnetic fields is respectable, equivalent to the field in the middle of a 1 cm2 circular loop carrying 23 A of current.  In most systems it ought to be pretty easy to keep currents that big suitably far away from the MRAM chip.

The operating temperature range, however, is a real limit.  Not going below 0 °C makes it suitable only for appliances that sit indoors in a heated office.  (I supposed you could design a heater into your circuit board, but what a pain.)  Presumably this will be improved in a future iteration.  There are all sorts of neat industrial applications for a nonvolatile RAM that doesn't wear out.

Verdict:  nifty and cool, but not quite ready for every application under the sun.

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