A friendly reminder that Flash is just another nv memory (no pun intended):
Computers to get a good, swift boot
Instant-on technology could make those long waits an old memory. Researchers are racing to develop magnetic systems called MRAM.
By Leslie J. Nicholson
INQUIRER STAFF WRITER
Anyone who has sprouted gray hair while waiting for a computer to boot up should take heart: Help is on the way.
In laboratories across the country, scientists are engaged in a quiet race to develop "instant-on" computers. Such machines would be up and running at the push of a button, just like a television set or a cellular telephone.
All it takes, the researchers say, is a new type of computer memory. Their candidate: a magnetic technology known as MRAM.
When a computer boots up, it grabs copies of the operating-system software (such as Windows or the Macintosh OS) and the application software (such as Microsoft Word) from the hard drive, and loads them into a temporary holding area called random access memory, or RAM.
On the hard drive, data are stored as magnetized regions on a rapidly spinning, rigid disk. In RAM, however, which is also known as main memory, the data are stored as electrical charges on semiconductor chips.
Because its data are stored magnetically, the hard drive retains information even without power. RAM chips, on the other hand, need a constant power source. They are therefore called a "volatile" form of memory.
Once a computer is turned off, all RAM data that have not been saved to the hard drive or to a disk are lost. Every time the computer is turned back on, the data must be brought back up into RAM.
The form of RAM found in most computers today is some variation of DRAM, dynamic random access memory. Of the many varieties of DRAM, the current favorite is SDRAM, which is short for synchronous dynamic random access memory.
DRAM is "dynamic" because it relies on power-storage units called capacitors. Capacitors leak energy, and must be fed new electricity every 15 nanoseconds. A nanosecond is a billionth of a second.
This constant refreshing "degrades the performance of the computer," said Stuart Parkin, a researcher at International Business Machines Corp.'s Almaden Research Center in San Jose, Calif. "You cannot access the memory while you're rewriting that memory."
Nonetheless, Parkin said, DRAM is popular because it is inexpensive and high-density, meaning a lot of DRAM chips can fit in a given space.
"In the microelectronics business, the cost of any device depends on how much real estate you take up on the silicon wafer," he said.
An alternative to DRAM is static random access memory, or SRAM. Unlike DRAM chips, they do not require constant refreshing. Plus, they are faster.
For each binary digit, or bit, of data stored, DRAM chips use a single transistor, which is a tiny switch that turns current on and off. SRAM chips use as many as six transistors per bit.
SRAM is more expensive than DRAM, and it takes up more space on a circuit board. For those reasons, SRAM is mainly used for cache, a memory subsystem where frequently accessed data are stored for quick access.
Another type of memory is flash memory. That is the kind found in digital cameras. It allows a device to come on instantly, data intact.
Flash memory is hard-wired onto a chip, but its contents can be erased and rewritten electrically. Flash is not considered fast enough or durable enough to serve as a computer's main memory, said Charles C. Morehouse, director of the Information Technology Lab at Hewlett-Packard Laboratories, Palo Alto, Calif. Flash chips break down gradually.
Enter magnetic random access memory, or MRAM.
MRAM is a developing technology that, according to researchers, might make its way into computers and other devices in five years or sooner.
It is being examined by several laboratories. IBM, H-P, Motorola Inc., Honeywell International Inc., Carnegie Mellon University and the Massachusetts Institute of Technology all have studied MRAM.
Proponents say MRAM will combine the nonvolatility of flash with the speed of SRAM and the density of DRAM. Besides making instant-on computers possible, MRAM chips could extend the battery life of portable electronics because of their low power consumption, IBM's Parkin said.
Depending on the lab, the first M in MRAM might stand for magnetoresistive, magnetic, or magnetic tunneling junction.
MRAM is similar to an old form of storage called core memory. In this form of memory, which emerged in the late 1950s, the memory cells were doughnut-shaped iron magnets that had wires running through them. Changing the direction of the currents in the wires caused the polarization of the rings to change.
A magnet polarized in one direction can represent a zero and one polarized in the opposite direction can represent a one. Therefore each magnetic ring can represent a data bit.
MRAM is a revolutionary advance over core memory, said Jian-Gang "Jimmy" Zhu, an engineering professor at Carnegie Mellon in Pittsburgh.
There are several approaches to MRAM. Here is one:
In place of the iron rings used in core memory, Parkin at IBM would use layers of a thin magnetic film separated by layers of an insulating material. The result is a kind of sandwich called a magnetic tunneling junction.
Passing current through wires above the junction will cause the polarity of the junction to change. The change in polarity affects the amount of resistance; that is, it determines how difficult a time electrons will have tunneling through the sandwich.
Each magnetic junction represents a bit of data, so the polarity of the junctions can be used to represent ones and zeros, the basic elements of binary computation. The magnets will retain this polarity even after the power is removed.
The stored data can be recalled later by sending voltage through the junction and measuring the resistance.
Whereas IBM is studying MRAM as an alternative to DRAM chips for main memory in computers, H-P Labs has different plans.
MRAM "has the chance, depending on how you use it, to be a really strong competitor to flash," Morehouse said. "We're aiming it at stand-alone chips, so they can be put in all sorts of things - a cell phone, a laptop, memory cards, all sorts of different things."
At Carnegie Mellon, Zhu has been working on MRAM for about five years in a joint project with Gary A. Prinz of the Naval Research Laboratory.
Zhu said their design, which they call VMRAM (for vertical magnetoresistive RAM), provides much higher density and stability than those of other labs because it uses doughnut-shaped magnetic structures rather than linear ones. The doughnut shape reduces interference and eliminates the need for transistors, he said.
The critical step for developing MRAM is to find a way to switch one memory cell without switching another, he said. The doughnut shape helps control magnetic flux, enabling the memory elements to be placed closer together.
"I think, within a year or two, you'll see some kind of MRAM," Zhu said. The first target will be the $10 billion flash-memory market, he said. "Flash memory is extremely slow. The MRAM memory is very fast. . . . It's just a matter of commercializing it."
Besides replacing flash and DRAMs, "there is also a possibility to replace disk drives in some applications," he said.
A system crash would be less of a disaster with an MRAM-equipped, instant-on computer, Zhu said.
"No, you don't lose everything. Your computer won't be completely down. If your computer crashes, you can just reload your operating system from your MRAM [rather than from the much slower hard drive]. It just would be a flash of seconds," he said.
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Leslie Nicholson's e-mail address is lnicholson@phillynews.com
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