Re: New ISA board to play with transputers

On 06 Jul 2025 17:09:25 +0100 (BST), Theo
<theom+news@chiark.greenend.org.uk> wrote:

john larkin <jl@glen--canyon.com> wrote:

Since CPU cores are trivial nowadays - they cost a few cents each -
the transputer concept may make sense again. We rely on an OS and
compiler tricks to get apparent parallelism, and the price is
complexity and bugs.
 
Why not have a CPU per task? Each with a decent chunk of dedicated
fast ram?

>
Intel tried that:
https://en.wikipedia.org/wiki/Xeon_Phi
>
(obviously using x86 was a bad idea, but apart from that...)
>
The issue is one of memory capacity and bandwidth.  Many applications have a
large (GB) dataset that doesn't partition nicely up between multiple nodes.
>
Even the largest FPGAs tend to have MB-scale amounts of memory on them, not
GB, because the memory density of a dedicated DRAM chip is so much better
than making on-chip BRAMs.  It turns out to be more efficient to use a large
external DRAM and drive it in a highly parallel way, pumping data through a
GPU-style core, than it is to have lots of little cores individually
fetching single words from their local BRAM.  With that model you also need
a fabric for the little cores to communicate, while with a big DRAM you get
inter-core/thread communication for free - you just arrange to a write to a
different part of the shared dataset and the next consumer picks it up.
>
You can of course put GDDR or HBM on an FPGA, but it's the same problem -
only a few devices must be shared by numerous cores.  Ultimately memory
throughput beats latency hands down, especially for large datasets.  This
was not such a problem in the Transputer's day, which is why that
architecture made sense.
>
Theo

Seems a shame to have an x86 core wasting time handling ethernet and
printers and mice and memory sticks when they could be doing better
things like running Spice.

My Windows 11 thing is running hundreds of processes right now. That's
crazy.

Computing is a mess. A new hardware architecture would at least
suggest a fresh start.