14.11.2012 Views

PC Architecture. A book by Michael B. Karbo

PC Architecture. A book by Michael B. Karbo

PC Architecture. A book by Michael B. Karbo

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Figure 220. This motherboard has an extra, built-in RAID controller, so there are four ATA connectors in<br />

total. Each one can handle two devices.<br />

Transfer speeds and protocols<br />

There are many ATA versions. The protocol has been changed over the years, but on the whole, the<br />

products are backward compatible.<br />

This means that you can readily connect an old CD-ROM drive which uses the PIO 3 protocol, for example,<br />

to a modern motherboard with an ATA/133 controller. The drive just won’t be any quicker as a result. The<br />

shift from parallel ATA/133 to Serial ATA is more profound. Here we use a different type of controller and<br />

new cables.<br />

The various protocols have different transfer speeds, as shown in the table below.<br />

Protocol Max. theoretical transfer<br />

rate<br />

PIO 3 13.3 MB/second<br />

PIO 4 16.6 MB/second<br />

Ultra DMA (ATA/33) 33 MB/second<br />

ATA/66 66 MB/second<br />

ATA/100 100 MB/second<br />

ATA/133 133 MB/second<br />

SATA 150 MB/second<br />

Figure 221. The various versions of the ATA standard.<br />

The transfer speeds listed apply to the interface. Few hard disks can deliver more than 80 MB/second, but<br />

even so, it’s still good to have the fastest possible interface. If two hard disks are used on the same<br />

controller, or if disks with a large cache are used, there can be a need for big bandwidth for short periods.<br />

With the ATA/66 standard, a new type of ATA cable was introduced. Hard disk cables normally have 40<br />

conductors, but in the new version this is extended to 80, as each wire is balanced <strong>by</strong> a ground connection.<br />

This reduces electrical noise and allows for greater bandwidth.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!