Post by Dave Taht Post by Mikael Abrahamsson
Nice resource, thanks.
If someone wonders why things look the way they do, so it's all about
on-die and off-die memory. Either you use off-die or on-die memory, often
SRAM which requires 6 gates per bit. So spending half a billion gates
gives you ~10MB buffer on-die. If you're doing off-die memory (DRAM or
similar) then you'll get the gigabytes of memory seen in some equipment.
There basically is nothing in between. As soon as you go off-die you might
as well put at least 2-6 GB in there.
There are some reasearch on new memory devices with unexpected results...
The HMC memory allows improvements in execution time and consumed
energy. In some situations, this memory type permits removing the
L2 cache from the memory hierarchy.
HMC parts start at 2GB
That effort actually looks pretty promising. I liked the support for
atomic ops too, offloaded.There are also so many useful operations
that I'd like to see offloaded to ram - like zeroing memory regions as
Will probably run hot. But: grump: I still don't "get" why the
traditional division between memory and cpu makers hasn't collapsed
yet. A package like that
with a cpu *in it*, and we're done. 4GB "ought to be enough for everybody".
27? years ago, back when I was attempting to write a SF novel, I had
an idea for a more efficient way to pack cores and memory together.
Basically: shrink the cray 1 design down to about the size of a nickel
The cray had that rough shape for optimum routing and cooling, but...
the overall shape of the package becomes a hexagon
(https://en.wikipedia.org/wiki/Hexagon) cylinder. That gives you 6 or
12 vertical flat surfaces to mount chips on (or just let them stand in
slots on the package). There's one natural crossbar bus at the center,
connecting the 6 "core" chips more rapidly than the edges. Top, bottom
and sides of the package can be used for I/O, power and so on, and
each hexagonal component wedged tightly together (instead of today's
north-south east-west architectures you get 2 more dimensions
fill the package with some sort of coolant. Seal it up tight. Test the
module as a whole and ship 'em in palletloads. I'm pretty sure the
heat circulates from the center out naturally, in every orientation,
but what the heck, stick in some MEMs fans in there to keep things
that design naturally led to 2 cpu chips and 4 memories. Or 4 cpu
chips and 2 memories. or 2 cpus 2 mems and 2 IOs. Before you started
coming up with things to do with the outer 6 sides.
I I never thought separating ram from cpu by more than a millimeter
was a good idea.....
It's a quite a jump to envision going from the cray-1 (115kw!!!) down
to the size of a nickel!
But everybody has a cray-1 now. They just run too hot. And are often
not suited to task, just like the cray was.
Don't know if anyone's ever tried to pattern any circuits on a cylinder though!
We are certainly seeing a lot of multi-package modules now (like in
epyc) but I'd like 'em to be taller and not need so many darn pins. A
full blown wifi
router on chip wouldn't need more than... oh... this many pins:
Post by Dave Taht
Thank you for that. I do have a long standing dream of a single chip
wifi router, with the lowest SNR possible, and the minimum number of
pins coming off of it. I'd settle for 32MB of (static?) ram on chip as
that has proven sufficient to date to drive 802.11n....
which would let you get rid of both the L2 and L1 cache. That said, I
think the cost of 32MB of on-chip static ram remains a bit high, and
plugging it into a mips cpu, kind of silly. Someday there will be a case
to just doing everything on a single chip, but...
Post by Mikael Abrahamsson
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