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New Features of Serial ATA Controller

The SerialATA controller integrated into the ICH6 South Bridges has also undergone certain changes. The major and most noticeable modification, which took place on transition from ICH5 to ICH6 is the increase of the number of supported Serial ATA-150 ports. If the previous generation chipset from Intel supported two Serial ATA ports, the current i925/i915 chipsets allow up to 4 Serial ATA ports. At the same time, note that the increase in the number of supported Serial ATA ports automatically led to fewer Parallel ATA ports. There is basically only one of those left now. In other words, the rapidly evolving Serial ATA standard started ousting Parallel ATA little by little, which is actually not at all surprising, keeping in mined that there are ever more storage devices supporting Serial ATA interface in the market every day.

The support of more Serial ATA channels couldn’t help telling on the functionality of ICH6R South Bridge supporting RAID arrays. Just like ICH5R, the latter also supports Raid 0 and 1 arrays, and the available four Serial ATA channels allow ICH6R building two arrays at a time. Despite our expectations, ICH6R doesn’t support RAID 0+1 arrays, because Intel engineers assume that you will hardly ever use 4 hard disk drives in a single PC system. However, Intel suggested a very interesting alternative to RAID 0+1 aka Matrix RAID.

Matrix RAID technology allows creating RAID 1 and RAID 0 simultaneously on only two hard disk drives. The idea behind this technology implies that each drive of the two is split into two parts. The first parts of both drives are used to create RAID 0 array, i.e. are used to store data which should be always available for fast access. The second halves of both disks are mirrored, that is used to build RAID 1 array, where the most valuable data are stored. From Intel’s viewpoint, the data should be stored in Matrix RAID array as follows: the first part of both drives, which is used to build RAID 0 array, should store operation system, applications and swap-file, while the second part of both drives with RAID 1 array on it should be used for user’s own files and data. This way, Matrix RAID technology ensures fast data access as well as higher data security with only two hard disk drives involved. In other words, Matrix RAID can turn out a good alternative to RAID 0+1 especially since you do not have to buy 4 hard drives to take advantage of it.

I would also like to stress that Serial ATA controller of the ICH6 turned into a fully-fledged AHCI device (Advanced Host Controller Interface). It actually appeared a prerequisite for “hot swappable” Serial ATA HDDs and for Native Command Queuing (NCQ) technology, which was borrowed by the ATA drives from the more expensive SCSI analogs. NCQ technology allows the HDD to rearrange the incoming data requests in order to reduce the latencies and increase the performance.

Only the actual device can rearrange the commands in the most optimal way, because it is the only one who actually knows the disk structure and the location of the read/write heads. That is why the implementation of NCQ requires appropriate support by the HDD, controller and driver. ICH6R and the corresponding new Intel Application Accelerator 4.0 driver do have this support. Therefore, Serial ATA hard disk drives supporting NCQ will be able to get a “free” performance boost once used with i925/i915 based mainboards.

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