[GTALUG] war story #2: buying RAM

[D. Hugh Redelmeier]

I wrote this thread to

1. inform others of the traps I encountered

2. to whine about how some traps are created to advantage vendors but end 
   up just making complexity that hurts everyone.

The RAM market is not simple.  There are several dimensions one needs to 
get right:

- technology (eg. DDR4 vs DDR5)

- socket (eg.  DIMM vs SODIMM)

- standard (eg. DDR4 is nailed down by JEDEC but XMP "goes beyond" that 
  standard).  This one really annoys me -- don't call it DDR4 and then 
  headline claims rquiring XMP without calling that requirement out.

- physical size (heat spreaders make some DIMMs too tall for my 
  application; perhaps they can also become too thick)

- ECC / no ECC.  This one is easy: you never get ECC without paying for 
  it, so it is usually clearly marked.  But it is not always clear 
  whether a computer supports ECC.  Random Ryzen system support ECC 
  (great!) but it depends on the motherboard and the vendors don't 
  highlight this.

- registered/unregistered.  Only servers, with a large number of RAM 
  sockets need this.  You might accidentally buy such a system used / off 
  lease.  It is a bit mysterious.  The reason is that each circuit has 
  limited "fan-out"; registered memory boosts the amount of fan-out 
  allowed.  You might also find some old registered memory cheap and then 
  find that you cannot use it.

- latency.  Lower is generally better.  It is a bit complicated -- there 
  are several latencies for a particular chip.  I just look at the 
  headline one.

Marketing has made that complexity unnecessarily hard to navigate.
Even a fairly knowledgeable consumer like me gets bitten by traps that 
should not be there.

RAM is a commodity.  You should not have to read spec sheets from 
manufacturers to discover if a module will work for you.  You should be 
able to go to any vendor and easily see what RAM they offer that would 
work for you.

Amazon isn't a bad way to buy memory.  But it doesn't let you search for 
RAM of the type you need.  Without selective search, there is a lot of 
slogging.  And, as I've described, the listings are misleading.

Other retailers are different but not clearly better.  I've looked at 
Canada Computers, Memory Express, and NewEgg.

ca.pcpartpicker.com doesn't get this completely right.

A couple of RAM manufacturers have product selectors that help you a lot.  
Lennart pointed this out.  But then you don't get the advantage of buying 
a commodity.