newfolder09

So it wasn't clear to me initially which phase of cpu development you meant. I agree with your statement regarding cpu development in the 90s. Looking at the performance equation I gave earlier, the second portion has gone from several 10s of cycles/instruction in the 486 timeframe to 2-3 INSTRUCTIONS/cycle for the Pentium III.

My point was that your statement about 90% of the gains being from Instructions/clock (ie. architecture) was not always true. The Pentium 4 being a prime candidate, where the number of pipestages was dramatically scaled up (reducing instructions/clock) to increase frequency.

WRT cost/die: Cpus are created on circular silicon wafers. http://arstechnica.com/hardware/news/2008/09/moore.ars/2 Every move to a lower process node, reduces the area for each cpu die. For a given cpu, this means that more of them can be added to each wafer, driving down the cost for each unit.

Ofcourse, as you mentioned, by keeping die size a constant , they get get more transistors/die, allowing them to cram more features on a chip. Lowering costs v/s adding features is a tradeoff that every cpu design team has to make.

As a general rule of thumb Performance for a given program for any CPU is : frequency times Instructions completed/cycle times number of instructions . The number of instructions is sort of fixed based on your ISA (ie. whether the machine is CISC like the x86 or RISC-like like the MIPS/ARM). What happened in the Pentium4 era, was that the focus was almost completely on the frequency part of the equation rather than the Instructions completed per cycle.

Intel's focus on new fabs is not just for a higher clock speed- that's a useful side benefit. The real reason is significantly lower cost/die. The same wafer can now produce many more cpu dies (that are slightly faster), increasing their profit/unit.

With regard to data centers, we are already seeing a move to power efficient architectures (with the Core family of cpus) versus pure performance. However, especially in the data center model, performance is still a critical metric that probably is not going away any time soon.