The best way to see the changes from the older 21064A to the 21164 is to compare them side-by-side (see table A). By the time you read this, the Alpha 21164A (a technology shrink of the 21164) will be available in systems that run at an unprecedented 433 MHz, and eventually 500 MHz! The 21164A moves from

the 0.5um process of the 21064/21164 to a 0.35um process, which allows for higher clock rates. It also adds 8-bit and 16-bit word-addressing capability, whereas the older CPUs can work only with 32-bit and larger words. And, the core voltage goes down from 3.3 volts (V) (40 watts (W) or more power dissipation on 300-MHz chips) to 2V (20W for 400-MHz+ chips) meaning lower power consumption at higher clock rates.

TABLE A: Feature Alpha 21064A Alpha 21164 New Benefits
  • CPU Clock Speed 200, 233, 275, and 300 MHz* 266, 300, and 333 MHz* Faster data and instruction
  • handling
  • Architecture: Data 64-bit, fully pipelined RISC, 64-bit, fully pipelined RISC, Fewer, simpler stages per pipe
  • multiple operating system multiple operating system (see below) for better
  • performance
  • Architecture: Instructions Superscalar (dual issue) Superscalar (quad issue) More instructions fetched and
  • 466 or 550 MIPS >1.2 BIPS retired per clock cycle
  • Floating Point Unit/Integer Unit 10-stage pipelined 9-stage pipelined Fewer stages mean fewer
  • 7-stage pipelined 7-stage pipelined instructions halted on a
  • branch
  • Memory Architecture 12-entry instruction translation 48-entry instruction TB, More available registers
  • buffer (TB), 32-entry data TB 64-entry data TB improve performance, allow
  • more flexibility in code
  • scheduling
  • Data Path 128 bits 128 bits with data pipelining Nearly double the data
  • throughput
  • Cache Memory (on-chip) L1: 16KB data, 16KB instruction L1: 8KB data, 8KB instruction More on-chip cache reduces
  • L2: 96KB unified likelihood of a cache miss
  • resulting in a slow memory
  • access
  • Performance Testing Chip- and module-level test Chip- and module-level test For developers and hardware
  • support support; programmable designers, improved on-chip
  • performance counters debugging tools reduce design
  • times

*Other CPU clock speeds are possible, as defined by individual vendors. By testing chips on a piece-by-piece basis, hardware developers can find those that operate at higher clock rates.