Le 2011/06/10 00:39, Darren New a écrit :
> On 6/9/2011 20:27, Darren New wrote:
>> The main difference between mainframes and smaller systems is that
>> mainframes are optimized for I/O. Even the mainframe I used 30 years ago
>
> Another example: The mainframe knew which disks were fast (having
> multiple heads per platter, for example) and which were slower, and it
> put the indexes of databases and directories and such (etc) on the fast
> disk and the bulk data and actual file contents on the slow disks. It
> also allocated random-access files on cylinder boundaries.
>
> Nowadays, the blades and desktop machines don't even know what the
> cylinder boundaries of their disks are.
>

You effectively can't know where the boundaries are when the drive never 
tels you the truth about it. The drive's organisation have been 
virtualised a prety long time ago, and each true cylinders may not have 
the same number of sectors as it's neibors. The OS sees all cylinders as 
having the same capacity. It also see a sectors, cylinders and heads 
count that don't have anything to do with the actual values.


Alain

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