What is the use of SATA

SATA / Serial-ATA

Serial-ATA, SATA or S-ATA for short, is an interface for connecting mass storage devices such as hard disks and removable storage drives. Interfaces for mass storage devices were originally always bus systems with parallel signal lines in conductor tracks and connection cables. With increasing transmission speed, technical difficulties arose which set an upper limit for the transmission rate. The ATA (EIDE) interface was not spared the fact that it was switched to a serial operating mode.

In 2000, several companies from the IT sector got together to create a specification for Serial ATA (Serial ATA). In 2001 the first version of Serial ATA was presented. At the beginning of 2003 the first controllers and hard disks were already available. It took until 2004 for full market penetration.
With 150 MByte / s, SATA is linked directly to the parallel EIDE interface (P-ATA) with 133 MByte / s.
The SATA interface supports 1.5 GBit / s with a net data rate of approx. 150 MByte / s. Hard disks with 10,000 revolutions per minute (rpm) deliver around 75 Mbytes / s of data. With SATA 6G, conventional hard disks reach almost 500 Mbytes / s (write speed).

The SATA interface has established itself very quickly for hard drives. SATA remained uninteresting for optical drives such as CD-ROM and DVD for a long time. A change in the market only took place when Intel abandoned the IDE / ATA interface in its chipsets. The computer manufacturers had to decide whether to install an additional IDE controller or SATA drives. Since it was not possible to do without an optical drive at that time, the SATA interface also caught on with optical drives.

SATA successor

SATA was accelerated twice with SATA-II and SATA 6G to a maximum of 600 MB / s. However, this is not fast enough for data storage devices with flash memory (SSD, Solid State Drive). However, there are SSDs that can read and write data at well over 1,000 MB / s. This also requires an interface that can handle this amount of data. SATA cannot do that. This is why SATA is being replaced by SATA Express (SATAe) or PCI Express (PCIe) as a mass storage interface.

Overview: SATA

interfacedescriptionTransfer rateRangeNumber of devicesintroduction
Serial ATASATA1.5 Gbit / s150 MB / s 1 m 42003
Serial ATA 2SATA-II3 GBit / s300 MB / s 1 m 162005
Serial ATA 3SATA 6G / SATA-6006 GBit / s600 MB / s 1 m 162007
Serial Attached SCSI (SAS)SAS3 GBit / s300 MB / s 1 m 16.3842004
Serial Attached SCSI 2 (SAS 2)SAS 6G6 GBit / s600 MB / s 1 m 16.3842007
Serial Attached SCSI 3 (SAS 3)SAS 12G12 GBit / s1,200 MB / s 1 m 16.3842010

Serial ATA architecture


Serial ATA uses up to four switched point-to-point connections. This means that each drive gets its own channel that it does not have to share with another device. This means that the installation effort is limited to installing the drives and connecting the cables. Old EIDE / ATA devices can be connected to the SATA controller using adapters.

technology

Serial ATA is completely compatible with parallel ATA (PATA). All commands, registers, PIO and DMA transfers, interrupts and also the master-slave behavior are emulated. Only the link layer packs and unpacks the serial data stream.
To ensure compatibility, the data available in parallel are converted into serial data streams using converters. The high integration density and the extremely fast internal processing speed in integrated circuits allow conversion almost in real time.
The electrical conversion and protocol adaptation only takes place on the lowest hardware level. The conversion from parallel to serial is carried out with an NRZ coding (8b / 10b). For this purpose, 1 byte is packed into a 10 unit on the transmission path. The two additional bits ensure that the edge changes are sufficiently frequent, which prevents the cable from being charged on one side.

Signal transmission

The signal level with SATA is only + -250 mV. This voltage is adapted to the usual generation of semiconductors. No complex level conversion between the transmission path and the controller logic is necessary.
Like every other modern serial transmission method, SATA works with differential signals on separate transmit and receive lines (TX- / TX + / RX- / RX +). In the case of differential signals, both lines change their levels at the same time but in phase opposition when the signal changes. The susceptibility to failure is thereby significantly reduced. Disturbances usually affect both lines, so that these disturbances can be almost completely removed when the difference is formed. The signal lines are usually twisted. However, the twisting leads to greater runtime differences at high data rates. Therefore, with SATA, the signal lines run parallel to the ground lines in a protective cover. This is why the SATA connector also has three ground connections.
Despite separate reception and transmission lines, SATA only allows half-duplex operation.

Plugs and connections


PATA connector (left) and SATA connector (right) in comparison


PATA connector (top) and two SATA connectors (bottom)


SATA connector


SATA power and data connector

A thin cable with a small connector is used to connect SATA devices. The wide ribbon cable from ATA was previously known.

The power connection is 15-pin, with three connections each for 3.3V, 5V and 12V, as well as 6 ground lines. The power cables can summarize the voltages and limit themselves to what voltages the devices require. In order to reduce power loss and thus the generation of heat, the drive electronics are operated with 3.3V.
The real reason for the high number of contacts is the hotplug capability. Each of the three voltages has a "pre-charge connection", which has a longer contact tongue that makes contact first when connected. The same applies to the data contacts (7-pin), which are spatially separated from the power supply.

mSATA / mini-SATA

mSATA is a standard of the JEDEC standardization committee that provides a PCIe interface instead of SATA for mini SSDs. Mini-SSDs are mainly connected to mini-PCIe slots in notebooks and, thanks to mSATA, are recognized as conventional SATA hard drives. The operating system can use standard drivers.

SATAe - SATA Express

SATA Express is the official successor to SATA 6G and uses a connector that is downwardly compatible with SATA 6G. This connector bundles two SATA ports that can be used either for SATA 6G or PCIe transmission. Because SATA Express masters both SATA-6G and PCIe. The SATAe-SSD has the form of a conventional hard drive.
With PCIe 2.0, SATA Express only brings 1 GByte / s and with PCIe 3.0 it would be "only" 2 GByte / s. This is far too little for many applications. SATA Express seems out of date even before it is widely used.

Overview: Interfaces for hard disks and removable storage drives

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Everything you need to know about computer technology.

Computer technology primer

The computer technology primer is a book about the basics of computer technology, processor technology, semiconductor memories, interfaces, data storage devices, drives and important hardware components.

I want that!