What is SATA or Serial ATA?

The full name of Serial ATA is Serial Advanced Technology Attachment, which is a hard disk interface specification jointly proposed by Intel, IBM, Dell, APT, Maxtor and Seagate. At IDF Fall 2001, Seagate announced the Serial ATA 1.0 standard, officially Announced the establishment of the SATA specification. ^[1]

The three stages of SATA development are shown below.

The first stage: the hard disk interface change period. With the continuous development of technology, the bottleneck of the transmission speed of parallel hard disks has become more prominent, so serial port technology has emerged. At that time almost all SATA was in the original

(1) SATA is an end-to-end serial bus

There are only one connector at each end of the SATA cable, one end is connected to the port provided by the host SATA controller, and the other end is connected to the serial port of the device. The connectors at both ends are exactly the same, and there is no problem of reverse connection. A SATA serial bus is connected to only one drive, and there is no problem with the master-slave drive of PATA, which eliminates the trouble of jumper setting and so on.

(2) SATA serial bus adopts low voltage differential drive

The ATA data line uses a differential drive technology called non-return to zero (NRZ). Data transmission in one direction is completed by two signal lines. When the voltage on one line is + 250mV, the voltage on the other line is -250mV, and vice versa, the voltage difference between the two lines is always maintained at 500mV. This differential drive effectively reduces the effects of various interferences such as electromagnetic radiation on the signal, and the receiver is easy to read the signal.

(3) The STAT cable is a full-duplex cable with a maximum length of 1 meter

The SATA cable has two sets of two data signal lines, which can carry out data transmission in two directions at the same time. It is a full-duplex serial cable. The cable connector is a 7-pin connector. In addition to the 4 data signal pins A +, A1, B +, and B-1, there are 3 ground pins. The ground wires are longer, so that when the connector is plugged and unplugged, the ground wire is connected first and then disconnected, which is conducive to the hot plugging of the device. SATA cables are slender and flexible, with a maximum length of 1m (39.37 inches), which is more than twice the maximum length of a PATA cable. 2.5m-long SATA cables have appeared on the market, and there is nothing wrong in using them, which fully shows that this kind of differentially driven serial cable has strong anti-interference ability.

(4) 8b / lOb encoding, built-in clock

Like the PCI Express bus, SATA also uses IBM's 8b / lob encoding method to transmit the data bit stream. 8b / 10b encoding is a method called RLL 0.4 encoding, where 0 represents the minimum number of consecutive 0s in a coded 10-bit symbol, and 4 represents the maximum number of consecutive 0s. The 8b / 10b encoding ensures that the receiver can reliably extract the synchronization clock from the bit stream, and also makes the voltage line interval on the signal line very even, the pulse waveform is regular and stable, and provides a stable load for the circuit.

(5) Very high working clock frequency, 150MB / s data transmission rate

The Serial ATA 1.0 specification defines that the bit flow rate of the SATA unidirectional data line is 1.5 Gbps, which is equivalent to the operating clock frequency of 1.5 GHz. Because 8b / 10b encoding is used, an 8-bit (1B) data is transmitted every 10 clock cycles, so the maximum data transmission rate is 150MB / s. From the beginning, it is higher than the maximum data transfer rate (100MB / s or 133MB / s) of PATA. The bitstream rates of the second and third generation SATA are scheduled to be 3.0Gbps and 6.0Gbps, and the maximum data transmission rates will reach 300MB / s and 600MB / S, respectively.

(6) Support interrupt aggregation

Although the maximum data transfer rate of SATA 1.0 is 150MB / s, due to the low efficiency of the interrupt delay and the capacity limitation of the motherboard SATA adapter, this theoretical maximum cannot be fully reflected in practice. To this end, the Serial ATA was formulated. The oa specification is used to guide improvements to the SATA bus environment, including host adapters and hard drives. The following performance characteristics are Serial ATA. Supported by the oa specification. One important technique is native command queuing (NCQ). NCQ technology can optimize the execution order of hard disk work tasks, select the most efficient way to read data, and intelligently manage the sequence of commands waiting to be executed inside the hard disk. NCQ uses advanced data management methods to increase the data transmission rate.

(7) Support first party DMA technology

DMA is a way of exchanging data directly with the memory without going through the CPU. There are two types of DMA methods: third-party DMA and first-party DMA. Third-party DMA is the standard DMA method we are familiar with, and its third party is the DMA controller. The DMA controller and CPU on the motherboard are potential masters of the system bus. Only after the system bus control is obtained through arbitration, can the DMA controller establish a DMA channel and complete data transfer. The first-party DMA method is the completion of the above functions and the realization of DMA transmission by the logic circuit of the interface, without the intervention of a third-party DMA controller at all. Since the information path to the third party is cancelled, the efficiency of DMA transmission is improved. ^[2]