AMD is enjoying its resurgence against Intel partly by moving more aggressively in new directions, such as multicore processors and 64-bit x86 extensions. But Intel is catching up, forcing AMD to hunt for the next big thing. AMD’s most recent maneuver is to license a radical new memory technology called Z-RAM.
Z-RAM is from Innovative Silicon, a start-up company in Switzerland. The technology is based on experiments by university researchers in Belgium who were stalled by a technical roadblock in 1990. In 2001, a Swiss engineer came along and solved the researchers’ biggest problem. That engineer co-founded Innovative Silicon, which has spent years perfecting the technology. But the company is too small to compete as a chip manufacturer, so it’s licensing Z-RAM to other companies.
Z-RAM exploits an electrical phenomenon called the floating-body effect. (Innovative Silicon calls it the Cinderella effect.) Some transistors have an extra insulating layer to reduce unwanted capacitance. Despite this, they still retain some capacitance, which slows them down. But Z-RAM uses the residual capacitance to store a binary state (0 or 1), turning the transistor into a one-bit memory cell.
Normally, a one-bit DRAM cell needs a transistor and a capacitor. Z-RAM needs only a transistor, which doubles as a capacitor (hence the name Z-RAM: zero capacitors). Thanks to this trick, Z-RAM is smaller and faster than conventional DRAM. Although Z-RAM isn’t faster than SRAM, it requires much less space, because SRAM bit-cells have four to six transistors.
Z-RAM isn’t fast enough to replace SRAM in L1 caches, but it could replace SRAM in the slower L2 or L3 caches. Depending on design goals, Z-RAM caches could have five times the memory capacity of equal-size SRAM caches, or they could provide the same capacity while occupying only one-fifth as much area on chip. Either way, Z-RAM is potentially a big advantage.
Now here’s the catch: Z-RAM works only with silicon-on-insulator (SOI) transistors. That’s no problem for AMD, which has been using SOI for years. But Intel has steadfastly resisted SOI and has no plans to adopt it. If AMD can successfully integrate Z-RAM into future processors, it will be a new direction that Intel can’t follow without reversing course.