Merced, EPIC, & IA64 Explained

by Ga'ash Soffer on November 11, 1998 3:10 PM EST
Digital brought us the first 64bit processor around 1992, the 21064. Sun Microsystems followed, and IBM came soon thereafter. The largest CPU manufacturer in the world (Intel); however, is waiting until early 2000 to introduce its first 64bit processor, Merced. This 64bit processor is not only new to Intel, but new to the world. Based on Intel's "EPIC" architecture (actually very similar to VLIW = Very Long Instruction Word = a technique which originated in the early 1980s) , Merced, is going to be the first true processor of its kind. What exactly is EPIC? How does it help? Find out...

EPIC Features



Explicit Parallelism

128 integer registers

128 floating point registers

64 predication registers



  • 20x FPU performance of Pentium Pro

  • 600+mhz, 0.18 micron process

  • first EPIC processor

  • Release date mid-2000


  • 2x as fast as Merced

  • 1Ghz+

  • 0.13 micron, copper technology

  • 2001+


  • Next generation Mckinely core

  • 0.13/ copper

  • 1Ghz+

  • 2002


  • Desktop IA64

  • 2003


EPIC Features Summarized

Before I go in-depth about certain topics (Predication, Speculation, Registers, etc.) I am going to give you a basic idea about EPIC and what it is. The basic idea behind EPIC is parallelism. Current processors must analyze code on the fly to determine the best execution path. An EPIC processor leave the compiler to do the dirty work of arranging the code to benefit from parallelism. This is known as EXPLICITLY PARALLELISM; the code is explicitly arranged to take advantage of parallelism. Since the EPIC processor is based on the idea of explicit parallelism; this processor must be capable of processing lots of data in parallel. EPIC processors have multiple instruction pipelines, generally many registers, wide data paths, and other special features such as Predication and Speculation to aid them in keeping the code highly "pipelineable" and to avoid stalls at all costs. One of the main advantages of EPIC is the efficiency of it. Although efficiency depends on compilers, overall an EPIC processor can use more of it's processing power to process meaningful operations, rather than waiting for instruction fetches, flushing pipelines, etc. Another major advantage of EPIC is that predication, speculation, and explicit parallelism reduce branch mispredictions significantly, because most of the code is organized prior to execution to eliminate mis-predictions (The EPIC processor does not have to guess what to execute simultaneously, etc. the compiled code TELLS it what to do.) (Also, predication and speculation soften the penalty of mis-predicting branches, more on this later)

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