Bird Families

Stachyris striolata)


The talks about a new Serial ATA interface, evolutionarily replacing the current ubiquitous Parallel ATA interfaces (UltraATA / 100, / 133, etc.), have been going on for a long time. Suffice it to say that we wrote about it in detail more than two years ago (see, the final specification of the first version of this interface, Serial ATA 1.0, was adopted on August 29, 2001 (see, and a detailed design guide for Serial ATA 1.0 devices (see _ was released on April 5 this year - almost immediately after the spring Intel Developer Forum. Meanwhile, the incarnation of Serial ATA in new devices - primarily hard drives and disk controllers on motherboards - has been slow to reach consumers. It wasn't until this summer that Seagate announced new Barracuda ATA V drives, some of which feature this new interface. However, we are waiting for those discs to this day. Other disk builders (Maxtor, IBM, Western Digital) are also feeding promises.

Motherboard chipset manufacturers do not bother to rush to release controllers either: many of them have new chipsets with integrated Serial ATA scheduled for release only at the end of this year (for example, Intel's ICH5 south I / O hub in Springdale series chipsets and south bridge SiS965 from SiS). That is, at the moment, in fact, only manufacturers of discrete chips for ATA controllers can present their products for Serial ATA to court - these are Promise, High Point, Marvell and some others. However, Promise and High Point, according to their long-standing tradition, have always been the first to release controllers for the next new versions of ATA interfaces (UltraATA / 66, / 100, / 133), so Serial ATA chips were no exception.

In this article, we will take a look at the first production samples of Serial ATA controllers on popular motherboards. Thanks for the initiative should be given by ASUSTeK, which recently released several new-generation motherboards, for example, P4B533-VT on the i845G chipset and P4S8X on the SiS648 chipset (we discussed these motherboards in detail earlier in the article on , a distinctive feature of which is, in particular, the presence of a board controller of the new ATA interface (along with the old Parallel ATA). Since the current chipsets are not equipped with Serial ATA, ASUS engineers used separate controller chips for this interface, and different ones. This will give us the opportunity to look at Serial ATA from different angles. But before proceeding directly to the consideration of new pieces of iron, let us briefly recall the main features of the new interface, with which we will have to work for the next 10 years, or maybe more.

The preconditions and prehistory of the Serial ATA interface, as well as its basic characteristics, were discussed in detail earlier, therefore, in order not to repeat ourselves, we refer you to the article at Anyone can study the detailed specifications of version 1.0 of this interface, for example, on the official website in a 307-page document at the link, as well as on the ... Here we will simply list the main differences between the new serial interface and the old parallel one and touch upon the basic principles and ways of its implementation in hardware.

First of all, the cable for the new interface is fundamentally different from the previous 40- or 80-wire wide flat: the number of signal wires of the cable has been reduced to four (there is also a ground), and its allowable length has been increased to one meter. This contributes to a more compact package and better cooling conditions inside the computer case, and reduces the cost of construction. Here compact seven-pin connectors are connected by a narrow flattened cable about 8 mm wide and about 2 mm thick (see photo). Inside the Serial ATA cable there are 2 pairs of signal wires (one pair for receive and one for transmit), separated by three conductors of the common wire (“ground”). On the connector located on disks and motherboards, three "ground" pins protrude slightly beyond the signal pins to facilitate hot-plugging (hot-plugging of drives via Serial ATA without special adapters is provided).

Serial ATA and Parallel ATA cables.

Another advantage of Serial ATA is the higher bandwidth than Parallel ATA. The first version of the Serial ATA interface has a bandwidth of up to 1.5 Gb / s (this is about 150 MB / s for payload versus 100-130 MB / s for a parallel interface). However, in the future, the second and third generation of Serial ATA (after about 3 and 6 years) will increase the speed to 3 and 6 Gb / s, respectively.

In addition, since only one drive can be connected to each Serial ATA cable (two drives can be connected to parallel drives at the same time), the interface speed margin now seems to be very large. Indeed, if current IDE hard drives with a read speed of useful data from platters up to 50 MB / s have practically saturated the UltraATA / 100 interface (two such drives on one IDE cable can no longer coexist without a theoretical loss of speed, since in reality UltraATA / 100 gives approximately 90 MB / s streaming bandwidth) and came close to the limit of the UltraATA / 133 interface, then it will take a very long time for single disks to reach 150 MB / s (according to estimates, about 5 years, or even more), that is, even the first version Serial ATA is assured of a long life. In addition, the proximity on the same cable will no longer interfere with the disks due to the elimination of IDE bus latencies for switching between neighboring devices, which should also increase the speed of disk operation in computers with a competent implementation of controllers on motherboards.

The electrical framing of the interface has also been improved: now, instead of more than 20 five-volt lines (and five-volt signals in modern systems often require more complexity and more expensive circuitry, since most current digital microcircuits already operate at lower supply voltages), only two differential lines with a level difference of only 0 are used, 5 volts, which is perfectly compatible with modern integrated solutions.

Another important feature of Serial ATA is that the interface architecture changes lie only in the field of physical interface, and in registers and software it will be fully compatible with the current parallel ATA. Therefore, there will be no need to radically change the drivers. Moreover, in some cases, new drivers for Serial ATA are not required at all (!): The Serial ATA architecture is transparent to the BIOS and the operating system. In addition, Serial ATA (unlike parallel ATA) has error correction (ECC), and the integrity of the data transmitted over the cable will be guaranteed.

Backward compatibility of serial ATA with parallel will be implemented in two ways: combining chipsets that support the parallel ATA interface with discrete components that physically implement Serial ATA, and using adapters (dongles) that convert the parallel ATA bus into a serial one, and vice versa (see block diagram).

4 main options for implementing the Serial ATA interface.

The diagram shows the 4 main options for implementing the Serial ATA interface. The first is classic. The Serial ATA controller is directly connected to the Serial ATA drive. The second option is intended mainly for the very initial stage of introducing a new interface, when there are debugged UltraATA / 100 controllers (and similar ones) and disks with the same interface, and they can be connected via Serial ATA if the corresponding translator chips are installed at both ends. (dongles, these chips do NOT require special drivers). The remaining two options are later periods of adaptation (transition) to Serial ATA from Parallel ATA, when one of the devices is already Serial ATA, and the other is not yet. In this case, one interface translator does the job. Currently, we are closest to options "2" and "4" (we will consider them in this article), although with the advent of Serial ATA drives, we will return to the rest of the options.

Now let's see how Serial ATA controllers are implemented on ASUS P4B533-VT and P4S8X motherboards.

This board implements the classic version of an external translator from parallel to serial ATA (options 2 and 3 in the block diagram above). The pre-sale sample of the P4B533-VT board contained a dual-channel IDE-RAID controller UltraATA / 133 based on the Promise PDC20276 chip - two dual-channel Parallel ATA ports. The first ATA port of this controller (blue IDE connector) is connected to two bridge-translators from the parallel ATA interface to the Serial ATA interface, made on 88i8030 chips from Marvell (pictured). And next to them are two 7-pin Serial ATA ports (connectors). Thanks to this, the board gained additional flexibility in use, since it is possible to connect either up to 4 UltraATA / 133 disks to a RAID controller (for two parallel loops), or use the primary channel for two Serial ATA disks, and the secondary channel same time for old drives.

Serial ATA on the ASUS P4B533-VT motherboard.

At the same time, you can organize RAID arrays in the same way (a variant of such a connection is shown in the photo below).

Serial ATA and Promise IDE RAID on ASUS P4B533-VT.

Of course, in this version, the primary IDE port of the RAID controller can be used either for parallel (blue connector on the board) or for serial connections (you cannot combine them). Meanwhile, in the press release on the release of this board, the Promise PDC20376 chip is indicated, which combines one parallel ATA channel with two Serial ATA ports. This is the option that is used on the next ASUS motherboard - P4S8X.

In addition to two standard "chipset" UltraATA / 133/100/66/33 ports, the board is equipped with the latest Promise PDC20376 chip supporting one dual-channel UltraATA / 133 parallel port (in the photo - the blue "side" port on the right) and two Serial ATA ports (SATA 150 , on the sides of the Promise chip in the same photo), and for all of them (Promis ports) IDE RAID 0 and 1 functions are possible (including SATA drives). That is, in this motherboard, the developers have done without hubs-translators on the 88i8030 chips from Marvell, using a fresh integrated solution right away.

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Photo "Spotted-necked bird (Stachyris striolata)" can be used for personal and commercial purposes according to the conditions of the purchased Royalty-free license. The image is available for download in high quality with resolution up to 5184x3456.

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