Alpha 21364 to Ease Memory Bottleneck: 10/26/98

With processor speeds rapidly approaching the gigahertz mark, the shortcomings of today’s memory architectures are becoming all too apparent. Waiting a few hundred nanoseconds to retrieve data from main memory is tolerable for a 100-MHz CPU, but this delay turns into hundreds of cycles for a 1-GHz processor. Compaq’s Alpha processors are likely to be the first to reach that speed, and at this month’s Microprocessor Forum, the company previewed its solution to this problem, embodied in the 21364. The 21364, code-named EV7, will use multiple Direct RDRAM channels to pump information from main memory right into the processor, greatly reducing latency. The 21364 certainly won’t be the first processor to include a DRAM controller; recent examples range from Cyrix’s MediaGX to Sun’s forthcoming UltraSparc-3. But the Alpha design presents a unique and elegant combination of a large on-chip L2 cache, direct access to DRAM, and a high-speed interprocessor connection. We believe this combination will become a common design for high-performance multiprocessor systems in the next decade. The 21364, which will wrap this new system interface around a 0.18-micron 1-GHz version of the current 21264 CPU core, is still early in its design phase. At the Forum, Alpha architect Pete Bannon said he expects the chip to tape out in late 1999, with shipments in late 2000 or early 2001. Thus, its main competition will come from future high-end processors such as UltraSparc-4 and Intel’s Merced. The Alpha chip’s projected workstation scores of 60 SPECint95 (base) and 100 SPECfp95 (base) set a high bar for competitors to leap, but the 21364 will truly soar in multiprocessor servers, where its lead could be greater.