🚀 go-pugleaf

In article <1gbpjrINNsq6@girtab.usc.edu>, plaw@usc.edu (Patrick Law) writes...
>Correct me if I am wrong. For the last 20 years, we have 4-bit 
>microprocessor, CISC, cache, RISC, superscalar, superpipeline,
>etc. Have we reached a point of diminishing return in uniprocessor
>design? Could we still get a speedup of "X" every "N" years like
>before? <text deleted>

Since the mid-70's, microprocessors have exhibited performance growth of
roughly 50% per year, within a given base architecture type (eg, CISC
processors, RISC processors, superscalar RISC processors).  Since circuit
speed has not improved as much (roughly 30% every process generation),
the balance has come by improved design and microarchitecture.  An example
from VAX history:

chip	year	process	cycle	rel	comments
				perf

MicroVAX 1985	3u	200ns	1X	No pipeline within microcycle

CVAX	1987	2u	 80ns	3X	'Half folded' pipeline within
					microcycle (ie, register writes
					overlapped with reads), onchip cache

CVAX+	1988	1.5u	 60ns	4X	Straight shrink

Rigel	1989	1.5u	 28ns	8X	'Fully folded' pipeline within
					microcycle (register read/ALU/register
					write overlapped, like classic RISC)

Mariah	1990	1.0u	 16ns	14X	Straight shrink + circuit tweaks

NVAX	1992	 .75u	 12ns	32X	Overlapped macropipeline -> lower cpi

In RISC, a comparable timeline would show the five stage pipe 'classic RISC'
employing more finely divided pipelines (for faster clock rates) and/or
multiple instruction issue, as well as improvements in memory hierarchy.

The ingenuity of processor designers (and semiconductor technologists) being
far from exhausted, I believe this performance growth can continue for the
rest of this decade.  There are some limiting factors:

- Process technology evolution appears to be slowing somewhat, due to
  lengthening development time (and cost) for new generations of semiconductor
  processing equipment.

- Increases in performance have been accompanied by increases in power
  consumption, in opposition to rising requirements for 'green' technology.

The shape of microprocessors in the year 2000 is the subject of a panel
discussion at the ISSCC conference, February 93.

Finally, the ability to continue improving uniprocessor performance does
negate the importance of cracking the programming problems on MIMD's and
other collectives.  An MPP could provide one to three orders of magnitude
more computing power.  Indeed, if the underlying microprocessors continue
to improve, so will the MPP.

Bob Supnik	>Supnik@human.enet.dec.com
		>All opinions expressed are those of a hardline microcoder
		>and do not reflect those of Digital Equipment Corporation