Digital Equipment公司推出的Alpha 21264是一款64位RISC处理器，采用创新的乱序执行设计，代表当时微处理器设计的前沿水平[1]。该芯片预计在1998年末上市，初期频率为500MHz和600MHz[1]，Digital预测其将在当年达到733MHz，并在2000年突破1000MHz大关[1]。
21264在单个时钟周期内可执行6条指令，同时处理80条指令，这一能力超越了Intel P6架构的40条和HP PA-8000的56条[1]。芯片集成15.9百万晶体管，采用6层金属0.35微米CMOS工艺，功耗为60瓦[1]。在缓存设计上，Level 1缓存配置为64KB指令缓存和64KB数据缓存，相比前代21164芯片的8KB有了显著提升[1]。芯片还搭载先进的分支预测机制，预测准确率约95%，错误预测率比21164降低了约一半[1]。
Samsung和Mitsubishi获得了Alpha芯片制造授权[1]，其中Samsung计划在2000年将21264推至1GHz[1]。Compaq规划在其高端Tandem服务器中使用21264处理器替换MIPS处理器[1]，同时制定了后续产品路线图，预计在2000年发布21364，2001年发布21464[1]。
Digital Equipment Corporation unveiled the Alpha 21264, a 64-bit processor engineered to deliver substantial performance gains through advanced microarchitecture innovations.[1] The chip, scheduled to debut in late 1998 at clock speeds of 500 MHz and 600 MHz, represents a significant leap in computing capability with an out-of-order execution design that Digital predicted would reach 733 MHz the same year and accelerate toward 1 GHz by 2000.[1]
The 21264 distinguishes itself through raw processing throughput and sophisticated instruction handling.[1] The processor can execute six instructions per clock cycle and maintain 80 concurrent instructions in flight—exceeding the 40 instructions handled by Intel's P6 architecture and the 56 supported by HP's PA-8000.[1] Manufactured using a 0.35-micron CMOS process with six metal layers, the chip integrates 15.9 million transistors and operates within a 60-watt power envelope.[1] The Level 1 cache configuration totals 128 KB—64 KB for instructions and 64 KB for data—a substantial increase from the 8 KB caches in the earlier 21164 generation.[1]
Branch prediction technology represents another advancement, with the 21264 achieving approximately 95 percent accuracy and reducing misprediction errors by half compared to its predecessor.[1] The architecture can process 1.2 billion floating-point operations per second.[1] Samsung and Mitsubishi hold manufacturing licenses for Alpha processors, with Samsung planning to deliver 21264 variants at 1 GHz speeds by 2000.[1] Compaq indicated plans to deploy the 21264 in high-end Tandem servers as a replacement for MIPS processors, while mapping future generations including the 21364 for 2000 release and the 21464 for 2001.[1]