Seagate ST33000651AS Set Features command, Aah, Enable read look-ahead read cache feature default

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10Ultra DMA mode 2 is currently active.

11Ultra DMA mode 3 is currently active.

12Ultra DMA mode 4 is currently active.

13Ultra DMA mode 5 is currently active.

14Ultra DMA mode 6 is currently active.

4.3.2Set Features command

This command controls the implementation of various features that the drive supports. When the drive receives this command, it sets BSY, checks the contents of the Features register, clears BSY and generates an interrupt. If the value in the register does not represent a feature that the drive supports, the command is aborted. Power-on default has the read look-ahead and write caching features enabled. The acceptable values for the Features register are defined as follows:

Table 8 Set Features command values

02H	Enable write cache (default).
03H	Set transfer mode (based on value in Sector Count register).
	Sector Count register values:
	00H Set PIO mode to default (PIO mode 2).
	01H Set PIO mode to default and disable IORDY (PIO mode 2).
	08H PIO mode 0
	09H PIO mode 1
	0AH PIO mode 2
	0BH PIO mode 3
	0CH PIO mode 4 (default)
	20H Multiword DMA mode 0
	21H Multiword DMA mode 1
	22H Multiword DMA mode 2
	40H Ultra DMA mode 0
	41H Ultra DMA mode 1
	42H Ultra DMA mode 2
	43H Ultra DMA mode 3
	44H Ultra DMA mode 4
	45H Ultra DMA mode 5
	46H Ultra DMA mode 6
10H	Enable use of SATA features
55H	Disable read look-ahead (read cache) feature.
82H	Disable write cache
90H	Disable use of SATA features
AAH	Enable read look-ahead (read cache) feature (default).

Barracuda XT SATA Product Manual, Rev. D 35