Editing DEC PRISM (section)

===PRISM===
Eventually, Cutler was asked to define a single RISC project in 1985, selecting Rich Witek as the chief architect. In August 1985 the first draft of a high-level design was delivered, and work began on the detailed design. The PRISM specification was developed over a period of many months by a five-person team: Dave Cutler, Dave Orbits, Rich Witek, Dileep Bhandarkar, and Wayne Cardoza. Through this early period, there were constant changes in the design as debates within the company argued over whether it should be 32- or 64-bit, aimed at a commercial or technical workload, and so forth.{{sfn|Supnik|2008}}

These constant changes meant the final ISA specification was not complete until September 1986. At the time, the decision was made to produce two versions of the basic concept, DECwest worked on a "high-end" [[Emitter coupled logic|ECL]] implementation known as '''Crystal''', while the Semiconductor Advanced Development team worked on '''microPRISM''', a [[CMOS]] version. This work was 98% done by 1985–86 and was heavily supported by simulations by Pete Benoit on a large [[VAXcluster]].{{sfn|Supnik|2008}}

Through this era there was still considerable scepticism on the part of DEC engineering as a whole about whether RISC was really faster, or simply faster on the trivial five-line programs being used to demonstrate its performance.  Based on the Crystal design, in 1986 it was compared to the then-fastest machine in development, the [[VAX 8800]]. The conclusion was clear: for any given amount of investment, the RISC designs would outperform a VAX by 2-to-1.{{sfn|Schein|2003|p=209}}

In the middle of 1987, the decision was made that both designs be 64-bit, although this lasted only a few weeks. In October 1987, Sun introduced the [[Sun-4]]. Powered by a 16&nbsp;MHz [[SPARC]], a commercial version of Patterson's RISC design, it ran four times as fast as their previous top-end Sun-3 using a 20&nbsp;MHz [[Motorola 68020]]. With this release, DEC once again changed the target for PRISM, aiming it solely at the workstation space. This resulted in the microPRISM being respecified as a 32-bit system while the Crystal project was canceled. This introduced more delays, putting the project far behind schedule.{{sfn|Supnik|2008}} 

By early 1988 the system was still not complete; the CPU design was nearly complete, but the FPU and MMU, both based on the contemporary [[Rigel (microprocessor)|Rigel chipset]] for the VAX, were still being designed.{{sfn|Supnik|2008}} The team decided to stop work on those parts of the design and focus entirely on the CPU. Design was completed in March 1988 and [[taped out]] by April.{{sfn|Supnik|2008}}