Le 2011-06-09 23:27, Darren New a écrit :
> 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.

Yep, or having separate front-end processors dealing with keeping the 
user sessions alive, etc.  Leaving the CPUs deal with important stuff.

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

Or some high-end server network cards implement the basic functionality 
of the IP stack, or SSL encryption in hardware.

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