Serial ATA – or simply SATA – is the hard disk standard created to replace the parallel ATA interface, a.k.a. IDE. The conventional IDE port (now called parallel ATA or simply PATA) transfers data in parallel. The advantage of parallel transmission over serial transmission is the higher speed of the former mode, seeing that several bits are sent at the same time. Its major disadvantage, however, relates to noise. As many wires have to be used (at least one for each bit to be sent per turn), one wire generates interference in another. This is why ATA-66 and higher hard disks require a special, 80-wire cable. The difference between this 80-wire cable and the normal 40-wire IDE cable is that it includes a ground wire between each original wire, providing anti-interference shielding. In our tutorial Everything you Need to Know About ATA-66, ATA-100 and ATA-133 Hard Disks we provide an in-depth explanation on this issue. The current maximum transference rate of the parallel IDE standard is 133 MB/s (ATA/133).
The problem in increasing parallel transmission transfer rate is increasing the clock rate, as the higher the clock rate, more problems with electromagnetic interference show up. Since serial transmission uses just one wire to transmit data it has fewer problems with noise, allowing it to use very high clock rates, achieving a higher transfer rate.
It is important to notice that SATA II and SATA-300 are not synonyms. One can build a device that runs only at 150 MB/s but using new features provided by SATA II such as NCQ. This device would be a SATA II device, even though it doesn’t run at 300 MB/s. Another advantage of using serial transmission is that fewer wires need to be used. Parallel IDE ports use a 40-pin connector and 80-wire flat cables. Serial ATA ports use a seven-pin connector and seven-wire cable. This helps a lot on the thermal side of the computer, as using thinner cables makes air to flow easier inside the PC case.
Here are the pinouts for both Serial ATA data cable and Serial ATA power supply cable. As mentioned before, Serial ATA uses two separated data channels, named A and B, using differential transmission, hence the + and – symbols below. On the wires marked with the minus signal, the data is an inverted copy of what is being transmitted on the corresponding wires with plus signal.
Because some SATA-300 hard disk drives don’t work correctly on motherboards with SATA-150 ports, some SATA-300 hard disk drives have a SATA-150/SATA-300 jumper (also known as 1.5 Gbps/3 Gbps jumper). The problem is that by default this jumper comes configured in the “SATA-150†position, limiting your hard disk drive performance if it is installed on a motherboard with SATA-300 ports. We will show you the performance impact of having a SATA-300 wrongly configured in a moment.
