Tom R. Halfhill
Look for new x86 microprocessors that integrate digital signal processor (DSP) functionality to arrive next year. These chips, some of which may ship as early as the first half of 1996, will perform some high-speed operations typically done by DSPs. Thus, they will give PC manufacturers a more integrated appoach to implementing such capabilities as software modems and MPEG playback than relying on separate, more expensive add-in cards.
Details were sketchy at press time, but three major x86 vendors -- Intel (Santa Clara, CA) Cyrix (Richardson, TX), and NexGen (Milpitas, CA) -- are reportedly going to announce "multimedia" CPUs in the coming months (see the table
"Likely Multimedia x86 Road Map"
).
DSP functionality is one intriguin
g new feature of a forthcoming processor from NexGen, which at press time announced that it will merge with Advanced Micro Devices (Austin, TX). The company is developing a new x86-compatible microprocessor that it says combines the best features of Intel's Pentium Pro (aka the P6) and a rumored "multimedia Pentium" (code-named the P55C). According to NexGen, the upcoming Nx686 chip will recognize a new subset of extended x86 instructions that mimic DSP operations, thus bridging the gap between CPUs and DSPs.
NexGen's chip integrates a DSP-like execution unit that's designed to greatly accelerate such multimedia functions as MPEG video decoding, audio playback, and 3-D graphics rendering. To make this practical, however, the extended instructions will require industrywide support from chip manufacturers, compiler vendors, and software developers. NexGen hints that a group of companies has been quietly working for months to gather that support and to standardize the extended instructions. Numerous compi
ler and OS vendors that BYTE contacted declined to comment.
The Nx686 implements the new instructions within a special DSP-like execution unit that uses a single-instruction/multiple-data (SIMD) architecture. The instructions are fairly general in nature, so they will work with a wide variety of algorithms. One example is multiply/accumulate (MAC), a common DSP instruction that repeatedly multiplies and adds a series of integers. NexGen says the Nx686 can execute as many as 6 billion of these operations per second, which is an impressive level of performance, even when compared to dedicated DSPs.
These chips won't be the first processors to marry DSP and CPU functionality: Current PowerPC processors, including the 601, 603, and 604, already implement DSP instructions, including MAC. And adding DSP functions to a CPU is not without controversy. DSP proponents caution that you can bring a CPU to its knees when you overload it with too many tasks.
AMD agrees. "High-performance CPUs combined
with low-cost DSPs is not a bad approach," an AMD representative says. "That's why we don't have a CPU that combines DSP functionality on our road map." However, with NexGen in the fold, AMD's position may now change.
One source that BYTE contacted, who wished to remain anonymous, says chip vendors might encourage applications developers to implement a few DSP operations that the CPU will handle well. In addition, the source says, other, more intensive DSP operations will be off-loaded to fixed-function or programmable DSPs.
AMD
Plans to market the NexGen Nx686 as the AMD-K6 in late 1996.
CYRIX
Plans to ship a 586-style multimedia processor in the first
half of 1996.
INTEL
Rumored P55C multimedia Pentium expected to ship in late 1996.
NEXGEN
Has been acquired by AMD (see sidebar "AMD Acquires NexGen's Nx686").
Multimedia x86 CPUs Coming in 1996
