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Startup Combines CPU and DRAM
MojoKid writes "CPU design firm Venray Technology announced a new product design this week that it claims can deliver enormous performance benefits by combining CPU and DRAM on to a single piece of silicon. Venray's TOMI (Thread Optimized Multiprocessor) attempts to redefine the problem by building a very different type of microprocessor. The TOMI Borealis is built using the same transistor structures as conventional DRAM; the chip trades clock speed and performance for ultra-low low leakage. Its design is, by necessity, extremely simple. Not counting the cache, TOMI is a 22,000 transistor design. Instead of surrounding a CPU core with L2 and L3 cache, Venray inserted a CPU core directly into a DRAM design. A TOMI Borealis core connects eight TOMI cores to a 1Gbit DRAM with a total of 16 ICs per 2GB DIMM. This works out to a total of 128 processor cores per DIMM. That said, when your CPU has fewer transistors than an architecture that debuted in 1986, there is a good chance that you left a few things out--like an FPU, branch prediction, pipelining, or any form of speculative execution. Venray may have created a chip with power consumption an order of magnitude lower than anything ARM builds and more memory bandwidth than Intel's highest-end Xeons, but it's an ultra-specialized, ultra-lightweight core that trades 25 years of flexibility and performance for scads of memory bandwidth."
This isn't new. The MIT Terasys platform did the same in 1995, and many have since. Nobody has yet come up with a viable programming model for such processors.
I'm expecting AMD's Fusion platform to move in the same direction (interleaved memory and shader banks), and they already have a usable MIMD model (basically OpenCL).
Speaking of unconventional design, why don't we see hexagonal or triangular CPU-designs? All I have seen are the Manhattan-like designs. Are these really the best? Embedding the CPU inside a hexagonal/triangular DRAM design should be possible too. What would be the trade-offs?
There are basically two problems:
1. The external connectivity -- SATA, USB, ethernet, etc. needs too much power to easily move or handle on a chip (and the radio stuff needs radio power). You can do the protocol work on the main chip if you like, but you'll need amplifiers, and possibly sensors off chip.
2. DRAM and CPUs are made in quite different processes, optimised for different purposes. Cache is memory made using CPU processes (so it's expensive and not very dense). These guys are trying to make CPUs using DRAM processes, which are slow.
Useless? My key question would be does it have decent speed integer multiply and perhaps even divide instructions. A whole heck of a lot can be achieved if you have, say, the basic instruction set of a 6809, but fast and wide (and it didn't even have a divide... so we built multiply-by-reciprocal macros to substitute, that works too.)
I know everyone's used to having FP right at hand, but I'm telling you, fast integer code and table tricks can cover a lot more bases than one might initially think. A lot of my high performance stuff -- which is primarily image processing and software defined radio -- is currently limited considerably more by how fast I can move data in and out of main memory than it is by actually needing FP operations. On a dual 4-core machine, I can saturate the memory bus without half trying with code that would otherwise be considerably more efficient, if it could actually get to the memory when it needs to.
Another thing... when you're coding with C, for instance, the various FP ops can just as easily be buried in a library, then who cares why or how they get done anyway, as long as they are? With lots-o-RAM, you can write whatever you need to and it'd be the same code you'd write for another platform. Just mostly faster, because for many things, FP just isn't required, or critical. Fixed point isn't very bard to build either and can cover a wide range of needs (and then there's BCD code... better than FP for accounting, for instance.)
Signed, old assembly language programmer guy who actually admits he likes asm...
I've fallen off your lawn, and I can't get up.