The latest incarnation of Intel's Pentium processor does more than simply run faster than the older 60- and 66-MHz versions. In fact, along with the availability of Windows NT 3.5, the latest Pentium should make dual-processor architectures a cost-effective option in the desktop workstation market. The P54C Pentium runs faster, comes in a smaller package, operates at 3.3 V, and adds special support for dual-processor designs.
High-end multiprocessor systems implement a dedicated cache for each processor, but sharing a single-processor cache between two processors enables a simpler, less-expensive dual-processor architecture. The system requires only one SRAM (static RAM) cache and a single cache controller. However, additional logic is also needed to arbitrate access to the shared bus and ensure cac
he coherency. The P54C Pentium has built-in hardware features to support cache coherency and bus arbitration (see ``Pentium's Dual Personality'' on page 211). Vendors can now implement a dual-processor architecture without worrying about designing additional logic to arbitrate a shared cache.
Xi Computer's XiP90 NTower DP came to us with an extra processor installed (right). Other units came with open slots for dual-processor upgrades. As the XiP90 proves, you can now buy a surprisingly low-cost dual-processor system. Or you can buy an upgradable model and pop in the second processor if your needs demand it. Of course, your software applications must support dual processing. Our standard low-level and application-level benchmarks do not exercise a second processor, so any performance enhancement effected by a dual-processor design will not show up.
This brings us to the second development that should boost the market acceptance of dual-processor systems: Windows NT. NT was built from the ground
up to support multiple processors. The NT kernel will spawn threads to each available processor. It simply allocates a dedicated processor to the next-highest-priority thread. New multithreaded NT applications, such as Picture Publisher, do not have to do anything special to take advantage of a dual processor. You run different threads for complex operations (e.g., applying a special-effects filter), and NT will do the rest.
Photograph: Xi Computer's XiP90 NTower DP has dual processors with heat sinks.
Photograph: The Xi Computer XiP90 NTower DP.
The Dual-Processor Pentium
