Serial ATA Technology
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On parallel buses, it is becoming increasingly more difficult to keep a synchronous flow of data on all lines especially at higher transfer rates. Furthermore, the non-specified bus connection on the IDE bus and the ground signals restrict the length of the cable used. Serial ATA uses LVDS (Low voltage differential signaling) for signal transmission similar to the LVD technology used successfully in SCSI.
The first Serial ATA generation is defined with a data rate of 150 Megabytes per second and is only slightly quicker than the fastest parallel ATA interface at the moment (ATA/133). The current Serial ATA II version doubles throughput to 300 MB/s. A Serial ATA version with 600 MB/s is scheduled for 2007.
In practice, as far as the speed factor is concerned, it is irrelevant whether the hard disk drives are equipped with an IDE (P-ATA) or S-ATA interface as it is the HDD mechanism that governs the speed and not the data rate of the interface. This also applies when comparing hard disk drives with SATA-150 and SATA-300 connections. What's more important is the HDD performance capacity which depends on the drive's access time, latency (rotational speed) and data rate.
Serial - ATA 300 MByte/s
Companies such as Western Digital, Samsung and Hitachi as well as Seagate manufacture SATA/300 hard disk drives with a maximum 750 GB. SATA/300 was launched at the start of 2005. The actual data transfer rate of SATA/300 is a maximum 300 MB/s, theoretically twice as fast as the first 1st SATA generation.
Features of SATA2:
A SATA2 hard disk drive does not have to deliver all these features at the same time. For example, a SATA hard disk drive can have 150 MB/s, NCQ and HotPlug but still be a SATA2 hard drive. Only a handful of the new Intel and Nvidia-nForce-4/5 boards support SATA II, other boards can only reach a rate of 150 MB/s. This is not a decisive factor governing the performance capabilities of the disks as the data rate of today's HDDs is less than 100 MB/s due to the hard drive's technology. Some companies incorporate the data transfer rate into the product name and use formulations like ?SATA 3.0 Gbps?.
The first Serial ATA generation is defined with a data rate of 150 Megabytes per second and is only slightly quicker than the fastest parallel ATA interface at the moment (ATA/133). The current Serial ATA II version doubles throughput to 300 MB/s. A Serial ATA version with 600 MB/s is scheduled for 2007.
In practice, as far as the speed factor is concerned, it is irrelevant whether the hard disk drives are equipped with an IDE (P-ATA) or S-ATA interface as it is the HDD mechanism that governs the speed and not the data rate of the interface. This also applies when comparing hard disk drives with SATA-150 and SATA-300 connections. What's more important is the HDD performance capacity which depends on the drive's access time, latency (rotational speed) and data rate.
Serial - ATA 300 MByte/s
Companies such as Western Digital, Samsung and Hitachi as well as Seagate manufacture SATA/300 hard disk drives with a maximum 750 GB. SATA/300 was launched at the start of 2005. The actual data transfer rate of SATA/300 is a maximum 300 MB/s, theoretically twice as fast as the first 1st SATA generation.
Features of SATA2:
- NCQ: Native Command Queuing. This standard optimises and accelerates the management of read/write requests. NCQ has to be supported by the hard disk drive, controller and driver.
- eSATA: external SATA for external drives, maximum cable length: 2 metres
- 3 Gbit/s data rate often referred to as 300 MB/s
- HotPlug: the ability to remove and replace the drive during operation without having to shutdown the system first.
- Staggered spinup: activation of multiple drives in sequence to avoid power surges
- Port multiplier: if more than four drives are needed in one computer or server, a port multiplier can be used to reduce the amount of cable required. With one cable running to the computer, this offers four or more (up to 15) ports on the drive side for short cables. The drives share the transfer bandwidth available. For example, with 50 MByte/s per drive, three drives can overload a 1.5 Gbit/s path (150 MByte/s). However, it is not often the case that three drives need to transfer with full bandwidth simultaneously. There should be enough bandwidth with a 3 Gbit/s (300 MByte/s) interface.
- Port selector: a port selector can be used to switch between two redundant transfer paths. This avoids the Single-Point-of-Failure (SPoF) problem: Two computers can then have access to one drive. However, both computers have to decide who is active (one at a time). Non-specified mechanisms can make this decision/switchover.
- xSATA: xSATA enables the drives to be at a further distance (max. 8 m, as with Serial Attached SCSI) from the computer than with eSATA. However, different cables and connectors are required.
A SATA2 hard disk drive does not have to deliver all these features at the same time. For example, a SATA hard disk drive can have 150 MB/s, NCQ and HotPlug but still be a SATA2 hard drive. Only a handful of the new Intel and Nvidia-nForce-4/5 boards support SATA II, other boards can only reach a rate of 150 MB/s. This is not a decisive factor governing the performance capabilities of the disks as the data rate of today's HDDs is less than 100 MB/s due to the hard drive's technology. Some companies incorporate the data transfer rate into the product name and use formulations like ?SATA 3.0 Gbps?.