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 timetransfer 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.
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 ModeCycle time (ns)Transfer rate (MB/s)Notes 06003.3these are the old ATA modes 13835.2 22408.3 3180 IORDY11.1These are the newer ATA modes 4120 IORDY16.6 The ATA-2 specific modes (3 and 4) use IORDY hardware flow control. This means that the drive can use the IORDY line to slow down the interface when necessary. Interfaces without proper IORDY support
