The big question on cell phone manufacturers' and memory vendors' minds these days is whether we need both NOR and NAND FLASH memory. Can one NAND device solve all the future memory needs in the handset?
According to Alan Varghese, ABI Research's senior director of semiconductors research, the answer may mean a "changing of the guard", as large NOR players Intel, AMD and Fujitsu feel the heat, and the NAND camp, including Samsung, Toshiba and Renesas, grab market share.
Varghese asks, "What are the disadvantages of NAND when applied to the modem side? Since NAND cannot do random access, we need a significant amount of attached DRAM into which the modem instruction code can be shadowed and run." This solution increases power consumption and adds latency at boot-up time; and, NAND is also not as robust as NOR in terms of data integrity, so additional error checking and correction are required. These disadvantages carry a financial cost.
Secondly, NOR's model of execute-in-place has been familiar to designers for the last 10-15 years; NAND requires a different code design methodology, at a time when anything that affects time-to-market is frowned upon.
"The transition point," Varghese says, "may be when the (cost-per-bit of NAND, plus the additional cost due to its disadvantages) is still less than the cost-per-bit of NOR FLASH."
More decisively, NOR FLASH is currently limited to a maximum size of 128Mbits while NAND reaches multiple Gigabits. The transition may be forced when the modem code and data to support the various cellular and communications protocols grow too large for NOR memory, and will only fit in NAND.