 | May 1, 2001 |
Silicon drive
ANALYSIS: New flash-memory option provides design advantages
Flash memory, in some form, has pervaded most all convergence applications. Products from cell phones to set-top boxes rely on nonvolatile flash to store both configuration and
personal data. Convergence teams, however have several ways of adding flash to a product. M-Systems is leading the way, reaching 32-Mbyte density with a hybrid disk/memory scheme called DiskOnChip.
Flash implementations range from direct linear addressing by a host CPU to hiding the memory behind the legacy ATA disk interface. In the latter case, the memory can reside on a removable module, like a CompactFlash card, or in a motherboard configuration, as is the case with Silicon Storage Technology’s ATA-disk Chip.
In either case, the disk interface hides the complexity of linearly reading and writing to flash, including the fact that flash chips from different vendors use completely different signaling schemes. Any OS that supports ATA can access flash placed behind a disk interface. In addition, some vendors, like Intel with its StrataFlash, offer software approaches that let you treat a flash device like a disk.
M-Systems offers a hybrid approach, combining flash with some interface logic that simplifies the CPU/flash interface and includes a low-level controller that provides disk-like functions.
M-Systems new DiskOnChip Millenium Plus offers the aforementioned 32-Mbyte density and is the company’s first true disk-on-monolithic-silicon product (as opposed to a multichip module). The technology still requires OS driver support, but M-Systems offers drivers for more than a dozen popular OSs.
The new offering provides a few other features that may be important for convergence applications. The device includes a 1-kbyte section of RAM from which a CPU can directly execute boot code using a linear addressing scheme. M-Systems claims this eliminates the need for a separate boot ROM in many applications, thereby lowering cost. The device also includes unique security features, such as a factory-written unique ID number that can prevent illegal cloning of devices such as set-top boxes. A private one-time-programmable area of the device can be used for sensitive data, and the nonvolatile memory can be partitioned into accessible and locked areas, with hardware protection for the locked partition.
The M-Systems offering is impressive and hits a price of $1.25/Mbyte in high-volume applications. Still, linear flash implementations will likely beat that price, and ATA-based products may prove more flexible.
—Maury Wright
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