On 6/9/2011 18:34, Francois Labreque wrote:
> There's also the question of performance. One needs a metric ton of
> bladeservers to be able to match the performance under load of a 20 year old
> mainframe sysplex.

The main difference between mainframes and smaller systems is that 
mainframes are optimized for I/O. Even the mainframe I used 30 years ago 
could do several I/O operations simultaneously faster than the CPU could 
handle it. For example, you could be swapping in/out three processes, as 
well as accessing the data and an index page of a database, while the CPU is 
running full speed. There were four IOPs for each CPU, and each IOP could 
handle two DMA channels.

Sort of like how video cards nowadays do all kinds of processing without the 
CPU's involvement other than setting them up.

-- 
Darren New, San Diego CA, USA (PST)
   "Coding without comments is like
    driving without turn signals."

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