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PC Hardware in a Nutshell, 3rd Edition
book

PC Hardware in a Nutshell, 3rd Edition

by Robert Bruce Thompson, Barbara Fritchman Thompson
July 2003
Beginner to intermediate content levelBeginner to intermediate
874 pages
38h 13m
English
O'Reilly Media, Inc.
Content preview from PC Hardware in a Nutshell, 3rd Edition

Programmed Input/Output (PIO) Modes

PIO is a means of data transfer that requires the CPU to intermediate data exchanges between the drive and memory. This dependence on the CPU places unnecessary demands on it and slows CPU performance under multitasking operating systems. Accordingly, modern drives and interfaces substitute DMA modes, described later, to provide high-speed data transfer. PIO modes remain important, however, when connecting older drives to newer interfaces or vice versa. Table 13-1 lists PIO modes, not all of which are supported by all drives and all interfaces.

Table 13-1. ATA PIO modes

PIO mode

Cycle time

Transfer rate

Revision

PIO-0

600 ns

3.3 MB/s

ATA

PIO-1

383 ns

5.2 MB/s

ATA

PIO-2

330 ns

8.3 MB/s

ATA

PIO-3

180 ns

11.1 MB/s

ATA-2

PIO-4

120 ns

13.3 MB/s

ATA-2

PIO-5

90 ns

22.2 MB/s

Never implemented

PIO Modes 0, 1, and 2 are not used on recent systems except to support older drives. Using PIO Mode 3 or 4 provides reasonably fast transfer rates, but requires that the drive support the IORDY line for hardware flow control. If the interface delivers data faster than a PIO Mode 3 or 4 drive can accept it, the drive de-asserts IORDY to notify the interface to stop delivering data. Running a drive that does not support IORDY on an interface configured for PIO Mode 3 or 4 may appear to work, but risks corrupting data. If you are not certain that your drive supports PIO Mode 3 or 4, configure the interface to use PIO Mode 2.

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Publisher Resources

ISBN: 059600513XErrata Page