Turn Your PC into a Powerful RISC Machine

Tom R. Halfhill

By integrating a Mips R4x00compatible CPU with an advanced memory architecture that obviates the need for a conventional SRAM (static RAM) cache, a Silicon Valley start-up has created a unique upgrade board that turns VL-Bus PCs into high-performance RISC systems for Windows NT. The board is offered as a low-cost alternative to a stand-alone Mips-based computer and as a one-box solution for dual-platform software developers.

Known as the Nitro-VLB Windows NT Booster, the board is the first product from ShaBlamm Computer ((408) 730-9696). The Nitro-VLB was expected to ship in May at prices ranging from $1095 to $2595, depending on the CPU/memory configuration. The board plugs into the VL-Bus slot of an 80x86-based PC.

Two key components of t he Nitro-VLB are its RISC CPU and memory architecture. The CPU is an Orion R4600, a Mips-compatible chip jointly developed in 1993 by Integrated Device Technology (Santa Clara, CA) and Quantum Effect Design (San Jose, CA) and manufactured by IDT and Toshiba America (Irvine, CA). At 100 MHz, the 64-bit R4600 is rated at 73.8 SPECint92 and 63 SPECfp92--about the same as a 66-MHz Pentium, although the R4600 chip sells for roughly half the price. Higher-end versions of the Nitro-VLB will use R4600 chips clocked at 133 and 150 MHz.

To enhance performance even further, Sha-Blamm uses 4 MB of memory on the PC's motherboard as a DMA buffer and populates most versions of the Nitro-VLB with 16 or 32 MB of interleaved EDRAM (enhanced DRAM). EDRAM is an advanced memory technology from Ramtron (Colorado Springs, CO) that integrates 2 Kb of 15-nanosecond SRAM with 4 Mb of 35-ns DRAM on a single chip. This eliminates the need for a secondary CPU cache based on SRAM; in effect, the main memory is the cache. ShaBlamm s ays this design is very effective when running a preemptive multitasking operating system, such as Windows NT, that would frequently miss a smaller SRAM cache as the CPU handles several large applications.

At $1995, the Nitro-VLB comes with a 100-MHz CPU, 16 MB of EDRAM, and Windows NT. The 150-MHz configuration costs $2595. The $1095 version has no memory and accepts standard 72-pin DRAM SIMMs instead of EDRAM. The performance of the $1095 version suffers by about 15 percent, but because DRAM chips are currently denser than EDRAMs, the memory can be expanded to 128 MB instead of 32 MB. Higher-density EDRAMs that allow expansion to 64 MB and 128 MB are scheduled to ship later this year.