Area: Diskovi.HR (CroatiaNet)
  From: Branko Panic
  To: Ivan Ivanisevic
  Subj: PIO

 Izvadak iz EIDE V1.9 FAQ-a:

  10.2.  What are PIO modes?

  The PIO mode determines how fast data is transferred to and from the
  drive. In the slowest possible mode, PIO mode 0, the data cycle time
  can not exceed 600 nanoseconds. In a single cycle, 16 bits are
  transferred in or out of the drive. In a single sector, there are 256
  words (16 bits = 1 word); 2048 sectors make up a megabyte. So,
  mathematically,

  1 cycle      1 sector       1 megabyte             2000
  --------     ---------     ------------     =     ------     = 3.3MB/s
   600ns       256 words     2048 sectors           600ns

  So, the theoretical transfer rate of PIO Mode 0 (600ns cycle time) is
  3.3 megabytes per second.

  Here are the rest of the PIO modes, with their respective transfer
  rates:

     PIO mode     Cycle time   transfer rate
                  (ns)            (MB/s)

         0           600            3.3         ATA
         1           383            5.2         ATA
         2           240            8.3         ATA
         3           180           11.1         ATA-2, IORDY required
         4           120           16.6         ATA-2, IORDY required
         5            90           22.2         vaporware


  The first three, PIO modes 0 to 2, are old modes also present in the
  old ATA standard. The others (PIO 3 and 4) are ATA-2 specific and use
  IORDY hardware flow control. This means the drive can use the IORDY
  line to slow down the interface when necessary. Interfaces without
  proper IORDY support may cause data corruption in the fast PIO modes;
  in that you're stuck with the slower modes, and typically half the
  bandwidth.

  When interrogated with an Identify Drive command, a harddisk returns,
  among other things, information about the PIO and DMA modes it is
  capable of using.

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