On Tue, Jan 30, 2018 at 03:49:54PM -0500, D. Hugh Redelmeier via talk wrote:

Another example: ARM is just now (more than 30 years on) targeting
datacentres.  Interestingly, big iron has previously mostly been
replaced by co-ordinated hordes of x86 micros.

There are two different cases to consider when doing data centers:

• uniprocessors for individual tasks or trivially parallelizable ones
  
• multiprocessors for things that aren't parallelizable

Anybody can provide the first. The second is harder.

Mips had three MMUs, one of which was for each of the above cases and one was a trivial one for embedded, so 32-CPU Mips machines were available.

IBM and Sun spent lots of money designing backplanes that could support >= 32 sockets: Sun when so far as to license a Cray design when their in-house scheme failed to scale.

Until and unless chip vendors spend significant time and money on MMUs and backplanes, they won't have an offering in the second case, and will have chosen to limit themselves to a large but limited role in the datacentre.

--dave

-- 
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb@spamcop.net           |                      -- Mark Twain