Microcoded emulation puts new processor in x86 PC fray
Three developments in the microprocessor market may have a significant effect
on what PCs cost in a couple of years, as well as what's inside them and how
fast they run. A small design firm's work will interact with big decisions of
IBM and Motorola in ways that are hard to predict.
International Meta Systems, Inc. (Torrance, CA) has incorporated a hardware
emulation technology into a prototype RISC processor that it claims can
functionally duplicate popular processors like the 486 and 68040. The
prototype, designated the IMS 3250 has a microcoded instruction-decoding
emulation engine combined with a double-issue superscalar core. The engine
allows compatibility with other microprocessors. In a two-pronged business
approach, the company hopes to license the compatibility technology to makers
of RISC microprocessors, as well as sell its own processor designs. The first
version of the prototype, called 3250P, is a gate array with the emulation
microcode in off-chip memory.
With it, International Meta Systems claims to be able to emulate 486 and 68040
microprocessors on the same chip. The company also says that a machine based on
the chip could run Windows and Macintosh programs on the same machine (see
diagram). Along the same lines IBM has been rumored to be preparing a PowerPC
chip with 486 emulation, but no one else has claimed to be able to do the whole
Windows/Mac combination.
The 3250P hardware includes provision for condition-code generation and use,
which runs in parallel with other operations. Separate registers mimic the
target registers, including those of the floating-point unit. The 3250 emulates
the FPU in firmware, but nothing in the scheme prevents adding separate FPU
circuitry.
The company has completed Microsoft Windows compatibility testing on the IMS
3250P and is now verifying other features of the early silicon. It expects to
supply samples to selected potential customers in August. IMS is negotiating
with SGS-Thomson Microelectronics (Carrollton, TX) for foundry services.
Public information from International Meta Systems indicates that emulation of
one CISC computer, either the 486 or 040, requires a 6-K x 32-bit ROM for
emulation firmware along with decoding logic occupying a third the space of the
ROM. This is claimed to run 486 code 10 times faster than software emulation on
the same architecture. If the final product comes even close to the claim,
licensing could be an attractive option for any RISC manufacturer making a
serious effort in the PC business.
IBM, Cyrix, and Motorola
The wild card in all this is IBM, which dropped two bombshells last month.
Along with Motorola, it recently announced another PowerPC chip, the 604, which
contains over three and a half million transistors in a 0.5-micron five-metal
process. IBM also announced an agreement with Cyrix to make 486 and Cyrix's
Pentium-class M1 processor, due for production shortly after the 604 at the end
of this year.
The 604 uses quadruple dispatch into six execution units, speculative and
out-of-order execution, dynamic branch prediction, and register renaming to
project 160 SPECint92 and 165 SPECfp at an initial clock speed of 100 MHz. This
performance is way beyond that of any projected version of the Pentium. Unlike
the 601 (see Electronic Products, June 1993, p. 77; Nov. 1993, p. 17), the 604
has a pad ring and will be fabricated at both IBM and Motorola. The announced
goal is twice the performance of the Pentium at the same price.
The strategy already works with the Macintosh. For the first time in history,
the fastest Mac is faster than the fastest Intel-based PC, and at a lower
price. However, it is only faster on native Power Mac software. For PCs on the
other hand, the plan depends on Intel keeping Pentiums expensive.
But, if IBM becomes a major vendor of 486 processors at the same time, Intel
will likely fight back by cutting margin and bringing prices down faster than
it otherwise would have. This would cut the room for maneuvering in the PowerPC
camp. What will be bad for Intel may not be all that good for IBM and Motorola.
IBM's own ambivalence may put off the frequently touted demise of the x86
architecture for another generation.
–Rodney Myrvaagnes
CAPTION:
The IMS 3250P prototype has ports for external microcode memory and host bus at
the top of the diagram. The “link stack” saves microcode calls and returns. On
a monolithic version, to be produced with standard cells, the block labeled
“channel logic” is the interface to the world.
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