SATA

Published:2011/8/15 1:34:00 Author:Amy From:SeekIC

Karel Walraven



There is a new standard these days for connecting hard disks and DVD drives: SATA. You may already have noticed that new PCs don’t contain the wide 40- or 80-pin ribbon cables any more, but the hard disk is connected with a slender 7- way cable. Even the corresponding power supply connector is different with a SATA drive and now has 15 connec­tions instead of 4. This is clearly illustrated in the drawing: The large connector pro­vides power and the small connector is the data connection. The power supply connector provides 12, 5 and 3.3 V and two ground connections.

SATA means Serial ATA. ATA is the con­nection standard that at present has been the most common for hard disks, CD and DVD drives. At the time of writ­ing the ATA100 bus with a data transfer speed of 100 Mbyte/s is the most wide­spread. A number of manufacturers use the slightly faster ATA133 bus. That is pretty much the end of the line; it has not been possible for the industry to increase the speed even further using simple means. In order to increase the speed of the interface between motherboard and HDD, a serial connection was selected. At first glance this appears to be a per­plexing choice! The parallel ATA bus operates with 16 bits simultaneously; the serial bus therefore has to be at least 16 times faster to obtain the same equiva­lent speed. That is why SATA operates at a clock speed of 1500 MHz and reaches a data transfer speed of 150 MByte/s; versions with 3 GHz and 6 GHz clock speed are planned.

The industry made this choice because, in the end, it is cheaper to have a solution with one data channel at very high speed than trying to increase the speed of all 33 signals in the ATA connection. The data connection has a balanced outgoing and a balanced return connection, plus three ground connections. The signal amplitude is not 5 volts any more, but only 0.25 volts. The symmetrical connection and the small signal amplitude together result in a fast, low interference and energy efficient connection. In addition, the cable is allowed to be much longer: 1 m instead of 45 cm with ATA.

Another big difference is that each device (HDD, DVD) has its own cable and connection to the motherboard. With the current ATA standard two devices can share the same cable. As a consequence various jumpers (master, slave) disappear and the interface can (in principle) always operate at maximum speed.

Additionally, the contacts in the connectors are of different length, so that hot-plugging (connecting or disconnection without switching the power off) becomes possible. The expectation is that this interface will satisfy the requirements for the next ten years.

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