- this term also has other meanings: PIO, aviation - Pilot Induced Oscillation
PIO - Programmed input / output (PIO ), a method of transferring data between two devices that uses the processor as part of a data route (the processor executes a read port command, reads a byte or data word into its register , and then overwrites it into memory , then repeats this procedure until all the necessary information is read from the device into memory).
Typically, this term applies to the classic PC / AT controller IDE / ATA / SATA . In this mode, the controller required the execution of the REP INSW/OUTSW processor command by the driver or the REP INSW/OUTSW to transfer all data, usually the command is executed in the controller interrupt handler in the "ready to transfer data" status.
The mode has significant drawbacks - I / O processor load and extremely low transfer rate due to the inability to use the “burst” mode of the PCI bus , and became outdated with the advent of DMA support in the IDE controller in the mid-1990s. But, firstly, if the PIO mode works the same in all PC-compatible computers, then the DMA implementation depends on the controller manufacturer (usually Intel , VIA or nVidia ) and requires the installation of drivers / kernel assemblies supporting these drivers. More or less modern versions of Windows will automatically install DMA drivers for any common IDE controller.
IDE / SATA controllers that are not compatible with standard PC / AT (HighPoint, Promise, Silicon Image, AHCI and others) do not have an outdated PIO mode as a method of transferring data between the processor and the controller. They always require driver installation (the driver is usually implemented as a SCSI controller driver) and always use the proprietary DMA implementation to communicate with the processor / memory, just like SCSI controllers.
Secondly, the inclusion of DMA mode affects not only the interface between the controller and the processor, but also the interface between the controller and the disk. Thus, to enable this mode, DMA support is also required in the hard disk or CD / DVD drive . Also, the PIO and DMA modes for the IDE are divided into several sub-modes indicated by numbers, which specify the data transfer speed over the cable. High DMA modes are called Ultra DMA and require a different parallel ATA cable - having 80 wires instead of 40. It has been supported since the early 2000s.
According to some reports, SATA cancels the implementation of these submodes, always using only one (high) cable rate. In practice, when using SATA hard drives connected to a non-PC / AT compatible Silicon Image controller with a proprietary driver, the selected PIO / DMA mode does not affect anything and is nothing more than decorating the user interface of the controller management utility and a relic of old times.
There are PIO modes 0, 1, 2, 3, 4. The larger the mode number, the faster. Iomega IDE ZIP100 drives, for example, can only provide PIO mode 0. Older CD-ROM drives typically use PIO mode 4 if they cannot operate in DMA mode.
- PIO Mode 0 = 3.3 MB / s
- PIO Mode 1 = 5.2 MB / s
- PIO Mode 2 = 8.3 MB / s
- PIO Mode 3 = 11.1 MB / s
- PIO Mode 4 = 16.7 MB / s
Specific Issues
On some computers, with automatic auto-detection of the appropriate PIO Mode, the system cannot boot from the CD-ROM, although the CD-ROM is perfectly detected. In this case, the CD-ROM works fine in an already installed operating system, as at that moment, the driver of the real processor mode not embedded in the BIOS is used, but the driver of the operating system loaded from the hard disk and working in protected mode.
The solution to this problem is to force PIO Mode 0. (Probably, you could try to pick a faster PIO Mode; however, the result usually does not justify the labor costs.)
If DVD / CD drive malfunctions or interface errors are detected (usually due to poor cable contact), the Windows operating system puts the disc into PIO mode. At the same time, significant delays in the operation of the system, hangs and loss of access to the disk are characteristic.