Understanding the SATA interfaces

The IDE interfaces were originally developed to use the ISA bus, used in computers 286. As with the ISA bus, 16 bits are transmitted at a time and used a large number of pins. As it is necessary to maintain compatibility with older devices, there is plenty of scope for changes in the pattern, so that even with the introduction of the PCI bus and PCI Express, IDE interfaces continue to function basically the same way.

Even when they were introduced ATA/66 interfaces, the only major change was the introduction of 80-wire cables, developed to allow higher baud rates, without changing the signaling system or the connectors.

From a certain point it became clear that the standard IDE / ATA was reaching its limits and that deeper changes could only be made with the introduction of a new standard. Then came the SATA (Serial ATA).

Just as PCI Express, SATA is a serial bus, which is transmitted one bit at a time in each direction. This eliminates the problems of synchronization and interference found in the parallel interfaces, in order to use higher frequencies.

As a result, the SATA cable is very thin, with only 7 pins, where 4 are used for data transmission (since you need 2 wires to close each of the two circuits) and 3 are neutral, that help minimize the Interferences

SATA cables are much more practical than the IDE cables and do not affect the flow of air inside the cabinet.The cables can be up to one meter in length and each SATA port supports a single device, unlike the standard master / slave IDE / ATA. Because of this, it is common for motherboards offer 4 SATA ports (or more), with only the plates of lower cost, including only two.

In the end, the performance gain allowed by the higher frequency of transmission has overcome the loss by transmitting a single bit at a time (instead of 16), causing, as well as simpler and cheaper, the standard SATA is faster.

There are three patterns of SATA controllers, SATA 150 (also called SATA 1.5 Gbit / s or SATA 1500), SATA 300 (SATA 3.0 Gbit / s SATA or 3000) and also the standard SATA 600 (or SATA 6.0 Gbit / s ), which is still in development. As SATA uses two separate channels, one to send and receive data to another, we have 150 or 300 MB / s in each direction, not 133 MB / s shared, as in the case of ATA/133 interfaces.

Names SATA 300 and SATA 3000 indicate, respectively, the throughput in MB / s "crude" rate, in megabits.SATA uses 8B/10B encoding system, the same used by the PCI Express bus, which are added 2 additional signaling bits for every 8 bits of data. These additional bits replace the synchronization signals used in interfaces IDE / ATA, greatly simplifying design and improving reliability of the bus. Thus, the controller transmits 3000 megabits, that due to encoding, up only 300 megabytes. That is, there is a rounding. :)

The SATA controllers 300 are popularly called "SATA II" so that the two terms ended up becoming synonymous. But, originally, "SATA II" was the name of the association of manufacturers who worked on the development of the SATA standards (including the SATA 300) and not the name of a specific pattern. Similarly, the standard 600 MB / s is called SATA 600, and not "SATA III" or "SATA IV. Even the manufacturers themselves hard drives do not usually use the term "SATA II", since it is technically incorrect.

Another curiosity is that many older motherboards equipped with SATA 150 controllers (such as those based on VIA VT8237 chipset and also the first review of the chipsets SiS 760 and SiS 964), have problems of compatibility with SATA 300. Because of this, most current hard drives offer the option of using a "compatibility mode" (enabled by a jumper), the DH is to behave as a SATA device 150 in order to ensure compatibility