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leave the door open for competing technologies such as magnetoresistive ran-
dom access memory (MRAM) to step in.
1.7.3 MRAM
MRAM
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is the first commercially viable solid state device to use the princi-
ples of “spintronics” that emerged from the discovery of the giant magneto-
resistive (GMR) effect (see Section 1.2.4). MRAM uses electron spin to store
information in its cell array. It offers many of the benefits of FLASH memory,
such as nonvolatile storage and low power, without suffering from the cell
wear-out that is inherent to NAND-FLASH technology. In addition to non-
volatile storage, it also promises to match the performance of SRAM (typically
used for CPU cache memory). The bit densities of MRAM are still an order
of magnitude below that of leading-edge FLASH memory implementations,
but the technology is maturing rapidly. It may prove to be a strong competi-
tor, and possibly the heir-apparent to FLASH memory in portable consumer
electronics devices. It is likely to compete with FLASH densities and cost-
competitiveness in the 2010 time frame, given current trends in the improve-
ment of this technology. In the short term, MRAM competes against FLASH
for lower-density applications that require DRAM-like write bandwidths.
1.7.4 Phase-Change Technology
Phase-change memory is another form of nonvolatile storage that is still in
developmental stages. Phase-change storage devices rely on using current-
induced heating to reversibly change the chemical composition of Chalco-
genide (GeSbTe) material between the cross-points of a wire mesh that forms
the storage array
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shown in Figure 1.5(a). The technology is further from
commercial introduction than MRAM at this time, but it has the potential
to scale much faster to high-bit densities using commercial manufacturing
processes.
1.7.5 Holographic Storage
Holographic storage promises to resolve the limitations that current optical
storage contends with in terms of increasing the capacity of a single disc.
Currently, optical storage is focused on decreasing the pitch of tracks or the
size of the data format in order to fit more data in the same form factor or limit
of a two-dimensional space. Holographic storage uses a volumetric approach
to storing data, such that data is not strictly limited by the two-dimensional
size of the disc. Holographic storage has been in development since at least the
1990s. No products are available in the market today, but the two companies
working on this technology have roadmaps that plan to deliver media roughly
the same as the current DVD that will hold 300 GB of data and be capable
of transferring data at a rate of 20 MB/s. The roadmap extends the media
