[GTALUG] New Deaktop PC -- To Run debian Linux - PCPartPicker Recipe;

[D. Hugh Redelmeier]

| From: o1bigtenor via talk <talk at gtalug.org>

| Not the OP but  - - - - one issue I'm seeing - - - my main system (its over
| 6 years old)
| has 8 slots for ram. Almost none of the newer mobos have that many.
| (Just one point for where newer isn't always 'better' (whatever that means!
| - - grin).)

My Sun 3/60 has 24 slots.  But the largest memory module that it will
accept is 1MiB (note: not 1GiB).  So more isn't always better :-)

As memory systems get faster, fan-out and signal path length matter
more.  So 4 is apparently the limit for "unbuffered" memory on one PC
memory bus these days.

If you have multiple processors on a motherboard, they probably have a
separate bus for each processor so you get 4 slots per processor.

If you have a big server, you use buffered memory (probably with ECC too)
and can have lots* of RAM sockets.  With buffering, you lose speed but
gain fan-out.

Complicating this is the market segmentation games that Intel is
playing.  Apparently you pay a lot for a Xeon processor that has enough
address lines.  AMD Epyc is smashing those limits so interesting
things might happen.

This supports 16 LRDIMM DDR4 modules, each could be 32GiB (I think).
2TiB in total (that's 16 x 128 GiB, so I'm missing something).
<http://b2b.gigabyte.com/Server-Motherboard/MZ31-AR0-rev-10>

In the good old days, bulk dynamic RAM chips were 1-bit wide so if
your bus was 32-bits wide, you could drive 32 chips with no fan-out on
the data lines.  Now RAM chips are typically 8-bits wide, modules are
64-bit wide, and busses are 64-bit wide, so fan-out is a larger
problem.

* "lots" is a technical term meaning more than four, but I don't know
how many