Serial ATA Tutorial
Serial ATA Explained
Serial Advanced Technology Attachment, or SATA, is a computer bus primarily designed to transfer data between computers and mass storage devices such as optical and hard disk drives. The advantages are faster data transfer, ability to hot-swap, thinner cables that let air cooling work more efficiently, and more reliable operation with tighter data integrity checks. The older technology has been retroactively named Parallel ATA, or PATA, and is expected to be replaced by the newer SATA standard. Serial ATA adapters and devices communicate over a high-speed serial cable.
Features
The current SATA specification can support data transfer rates as high as 3.0 Gbit/s per device. SATA uses only 4 signal lines; cables are more compact and cheaper than for PATA. SATA supports hot-swapping and Native Command Queuing. There is a special connector (eSATA) specified for external devices, and an optionally implemented provision for clips to hold internal connectors firmly in place. SATA drives may be plugged into Serial Attached SCSI (SAS) controllers and communicate on the same physical cable as native SAS disks, but SATA controllers cannot handle SAS disks.
Cables and connectors
Connectors and cables are the most visible difference between SATA and PATA drives. Unlike PATA, the same connectors are used on 3.5-in (90 mm) SATA hard disks for desktop and server computers and 2.5-in (70 mm) disks for portable or small computers; this allows 2.5" drives to be used in desktop computers without the need for wiring adapters.
Power
The SATA standard also specifies a new power connector. Like the data cable, it is wafer-based, but its wider 15-pin shape prevents accidental misidentification and forced insertion of the wrong connector type.
eSATA
eSATA defined separate cables, connectors, and revised electrical requirements for external applications:
- Minimum transmit potential increased: Range is 500–600 mV instead of 400–600 mV.
- Minimum receive potential decreased: Range is 240–600 mV instead of 325–600 mV.
- Identical protocol and logical signaling (link/transport-layer and above), allowing native SATA devices to be deployed in external enclosures with minimal modification.
- Maximum cable length of 2M.
- The External connector has no “L” shaped key, and the guide features are vertically offset and reduced in size. This prevents the use of unshielded internal cables in external applications.
- To prevent ESD damage, the insertion depth is increased from 5mm to 6.6mm and the contacts are mounted farther back in both the receptacle and plug.
- To provide EMI protection and meet FCC and CE emission requirements, the cable has an extra layer of shielding, and the connectors have metal contact points.
- There are springs as retention features built into the connector shield on both the top and bottom surfaces.
- The external connector and cable are designed for over five thousand insertions and removals while the internal connector is only specified to withstand fifty.
The Cutting Edge ~ Newest Technology
SATA 6.0 Gbit/s
SATA plans to introduce a 6.0 Gbit/s standard. In current PCs, SATA 3.0 Gbit/s already greatly exceeds the sustainable transfer rate of even the fastest hard disks. The 6.0 Gbit/s standard is useful in combination with port multipliers, which allow multiple drives to be connected to a single Serial ATA port, thus sharing the port's bandwidth with multiple drives.