[freeek]

HARD DISK DRIVE

Hard disk is a magnetic disk storage device that stores digital data on rotating magnetic surfaces. These are permanently mounted or "fixed" in the system and are not removable like floppy disks. The computer’s operating system and other software are installed on the hard disk. Since, the disk and the drive are usually contained in the same unit, hard disk is also known as "hard drive". Hard disks store more data and provide quick access to large quantities of data than floppy disks. Hard disks are needed to be formatted before they can store data.

Function:

The hard drive is a permanent storage space for data and the programs that are used to create the data. Inside the hard disk, both sides of an individual platter are covered with a special magnetic material located. These platters are fixed to the spindle and they spin at thousands of Revolution per minute (RPM)

The overall performance of the hard drive is dependant on the Revolutions Per Minute, which means the total number of revolutions made by a platter in 60 seconds. The speed at which the data can be read from the platters is directly proportional to the RPM. The values of RPM range from 5,400RPM to 12,000RPM and more.

Description:

Hard disk drive, a disk controller, jumpers, and a cable comprise a Hard Disk Drive system. Several computers have controller as a separate expansion board, which interfaces the system through an expansion slot. Direct cabling to the power outlet provides the power supply. Several hard drive interfaces are IDE, SCSI, IEEE 1394, USB etc.

Hard drives are available with several different storage capacities. The storage capacity of a hard drive is measured in megabytes (MB) and gigabytes (GB).The common storage capacities these days range from 40 GB to 120 GB and more. An ideal drive would be physically small, have fast seek times, spin fast, large buffers and a long warranty.

The drives that are connected externally by a cable to a special port are known as "External drives". The most common external drives are

HARD DRIVE PHYSICAL COMPONENTS:

PLATTERS:

Platter is a circular, metal disk that is mounted inside a hard disk drive. Several platters are mounted on a fixed spindle motor to create more data storage surfaces in a smaller area. The platter has a core made up of aluminium or glass substrate, covered with a thin layer of Ferric oxide or cobalt alloy. On both sides of the substrate material, a thin coating is deposited by a special manufacturing technique. This, thin coating where actual data is stored is the media layer. When the magnetic media is applied to the surface of the substrate material, a thin lubricating layer is applied to protect the material. This complex three layered media is discussed in detail as follows:

THE SUBSTRATE MATERIAL:

The bulk material of which platters are made up, forms the base on which media layer is deposited. The substrate has no specific function but to support the media layer. The most commonly used material for making this physical layer is an Aluminium alloy. This alloy is rigid, lightweight, stable, inexpensive, easy to work with and is readily available. Earlier, since the gap between the heads and the platter was relatively high, the platter surface being smooth and flat was less of an issue. However, as technology advances, the gap between heads and platters is decreasing and the speed that the platters spin at is increasing. For this reason demand for alternatives on the platter material are increasing. Glass platters are replacing aluminium platters because they provide improved rigidity, better quality, thinner platters, and thermal stability.

MEDIA LAYER:

The substrate material forms the base upon which actual recording media is deposited. The media layer is a thin coating of magnetic material applied to the surface of the platters and where the actual data is stored. Its thickness is only a few millionths of an inch.

Special techniques are employed for the deposition of magnetic material on the substrate material. A thin coating is deposited on both sides of the substrate, mostly by vacuum deposition process called magnetron sputtering. Another such method is electroplating, using a process similar to that used in electroplating jewelry.

PROTECTIVE LAYER:

On the top of the magnetic media, is applied a super-thin, protective, lubricating layer. This layer is called the protective layer because it protects the disk from damage caused by accidental contact from the heads, "head crash" or other foreign material from entering the drive

PLATTER DIVISIONS:

In order to get maintain the organized storage and retrieval of data; the platters are organized into specific structures. These specific structures include tracks, sectors, and clusters.

TRACKS:

Each platter is broken into thousands of tightly packed concentric circles, known as tracks. These tracks resemble the structure of annual rings of a tree. All the information stored on the hard disk is recorded in tracks. Starting from zero at the outer side of the platter, the number of tracks goes on increasing to the inner side. Each track can hold a large amount of data counting to thousands of bytes.

SECTORS:

Each track is further broken down into smaller units called sectors. As sector is the basic unit of data storage on a hard disk. A single track typically can have thousands of sectors and each sector can hold more than 512 bytes of data. A few additional bytes are required for control structures and error detection and correction.

CLUSTERS:

Sectors are often grouped together to form Clusters.

READ/WRITE HEADS:

The heads are an interface between the magnetic media where the data is stored and electronic components in the hard disk. The heads convert the information, which is in the form of bits to magnetic pulses when it is to be stored on the platter and reverses the process while reading.

The heads are the most sophisticated part of the hard disk. Each platter has two read/write heads, one mounted on the top and the other one at the bottom. These heads are mounted on head sliders, which are suspended at the ends of head arms. The head arms are all fused into a singular structure called actuator, which is responsible for their movement.

THE SPINDLE MOTOR:
Spindle motor plays an important role in hard drive operation by turning the hard disk platters. A spindle motor must provide stable, reliable, and consistent turning power for many hours of continuous use. Many hard drive failures occur due to spindle motor not functioning properly

HARD DISK LOGIC BOARD:
Hard disk is made with an intelligent circuit board integrated into the hard disk unit. It is mounted on the bottom of the base casting exposed to the outer side. The read/write heads are linked to the logic board through a flexible ribbon cable.

DRIVE BAY:
The entire hard disk is mounted in an enclosure designed to protect it from the outside air. It is necessary to keep the internal environment of the hard disk free of dust and other contaminants. These contaminants may get accumulated in the gap between the read/write heads and the platters, which usually leads to head crashes.

The bottom of the disk is also called base casting. The drive mechanics are placed in the base casting and a cover, usually made up of aluminium is placed on top to enclose heads and platters. The entire contents placed on the base and cover chamber are collectively known as the head-disk assembly. Once this assembly is opened, it would instantly contaminate the contents and eventually ruin the drive.
On the bottom of the base casting is present the logic board, which is separated from the base casting using a cushioning material.

TYPES OF HARD DRIVE CONNECTIONS/INTERFACES:

• SCSI
• IDE/EIDE/ATA/PATA
• SATA
• USB
• FireWire/IEEE 1394
• Fiber

SCSI:
Stands for small computer system interface and is a parallel interface standard used for attaching peripheral devices to computers at the same time, such as hard drives, printers, scanners, CD-ROM/RW drives, DVD drives and tape drives. SCSI connector provides for faster data transmission rates up to 320 Megabytes per second (320 MBps). SCSI provides higher data transfer rates than ATA.

SCSI SPECIFICATIONS:

There are three basic specifications:

SCSI-1:
SCSI-1 features an 8-bit parallel bus running at 3.5 MB/s in an asynchronous mode and 5 MB/s in a synchronous mode. SCSI-1 supports 8 devices at the maximum with the maximum cable length of 6 meters.

SCSI-2:
It features a 16-bit bus width doubling the maximum transfer rate to 10 MB/s. SCSI-2 supports up to 16 devices with the maximum cable length of 3 meters.

SCSI-3:
SCSI-3 uses a 16-bit bus and the maximum transfer rate to 320 MBps. It is also called Ultra Wide SCSI.Other specifications include: Ultra2 SCSI, Wide Ultra2 SCSI, Wide SCSI, Fast SCSI, Fast Wide SCSI, Ultra SCSI.

IDE/EIDE/ATA/PATA:
IDE (Integrated Drive Electronics); EIDE (Enhanced Integrated Drive Electronics); ATA (Advanced Technology Attachment); PATA (Parallel advanced technology attachment). It is an interface for mass storage devices, in which the controller is integrated into the hard disk, CD-ROM drive, and the floppy drive.The IDE interface uses advanced technology attachment interface for cable lengths up to 2 feet. A single IDE ATA channel supports up to two drives, master and the slave. At a time, IDE can only access one drive per channel.

IDE is less expensive than SCSI but offers less performance level. IDE interface could support drives up to 540 MB

SATA:
Serial ATA is an evolution of the parallel ATA interface. A single cable with atleast four wires creates a point-to-point connection between devices, which defines that serial ATA is a serial link. Serial ATA support data transfer rates starting from 150 MBps. Serial ATA cables can extend up to one meter. This interface supports all ATA and ATAPI devices. Serial ATA has thinner cables, hence, allow for smaller chassis designs. These cables can extend up to one meter.

Serial ATA is not backward compatible i.e. it will not work with the same connectors that IDE, SCSI or any other interface.

USB: Stands for Universal Serial Bus is an external serial bus standard to interface devices. USB is an external bus that supports three data transfer rate:

• A low speed rate of 1.5 Mbps, mostly used for human interface devices, such as mice, keyboards, and joysticks.
• A full speed rate of 12 Mbps supported by all USB Hubs.
• A high speed rate of 480 Mbps. The high speed devices are commonly referred to as USB 2.0.

A single USB port is capable of connecting up to 127 peripheral devices, such as printers, scanners, digital cameras, mice, keyboards, joysticks, modems, speakers, telephone, video phones etc.

Connecting a USB device to the computer requires the plugging of the USB device cable connector to the USB connector at the back of the computer. A typical USB socket at the back of the computer is rectangular. A USB standard uses two different connectors, "A" and "B". "A" connectors head upstream toward the computer and B connectors head downstream and connect to individual devices.

The main features of USB include:

+ Ease of Use.
+ The computer acts as a host.
+ Up to 127 devices can be connected to the host with maximum cable length of 5 meters for individual USB and 30 meters for USB hubs.
+ USB devices are hot swappable, i.e. they can be plugged and unplugged at any time.
+ USB supports Plug-and-Play installation.
+ High data transfer rate of 480 megabits per second with USB 2.0.

FireWire/ IEEE 1394:

The IEEE 1394 standard for High Performance Serial Bus, also called FireWire, is a way of transferring information between digital devices, mainly audio and video equipment.
FireWire is a very fast external bus that supports data transfer rates up to 400 Mbps via IEEE 1394a (FireWire 400), which is about 3 times faster than USB. A single IEEE 1394 port is capable of connecting up to 63 external devices with cable length up to about 4.5 m. IEEE 1394b (FireWire 800) is capable of transferring data up to 800 Mbps with the maximum cable length up to 100 meters. The 1394b standard is faster than 1394a and is backward-compatible. FireWire is plug-and-play, which means if a new FireWire device is connected to the computer, the operating system detects it automatically, or if any new device has been installed, the computer activates it. FireWire devices are hot pluggable, i.e. it allows plugging and unplugging devices at any time, even when the power is on.

The main features of FireWire include:

• Supports high data rate
• Plug and play
• Hot-pluggable
• Inexpensive
• Easy to use
• Ability to connect lot of devices on the bus
• Isochronous data transfer

In Isochronous mode, multiple, time-critical, multimedia data streams are delivered at a guaranteed rate.

FC-AL (Fiber Channel-Arbitrated Loop):
FC-AL is designed for high-bandwidth high end systems and is compatible with mass storage devices and other peripheral devices that require very high bandwidth. It supports serial mode of data transfer.

This interface uses optical fiber cable to connect the devices to produce a maximum data transfer rate of more than 100 MB/second. FC-AL loop links as many as 127 devices as far as 10 kilometers apart. FC-AL can be connected to two ports to double the data transfer rates. This interface is more expensive as compared to SCSI interface.

All devices in an arbitrated loop are similar to token ring networking. When one device stops functioning, the entire loop gets interrupted. To overcome this failure, channel hubs are present to connect multiple devices together.

The main features of FC-AL include:

• Serial data transfer for distances greater than 10 Km
• High data transfer rate
• Supports for a large number of devices
• Reliable for data transfer
• Compatibility with various already existing protocols
• Frames (data packets)

[Neo]

do u really want me to read all this????

thanks for sharin

[Skywalker]

thanks Dude
and New technology is also Alive

[freeek]

Hitachi Continues to Drive Notebook PC Capacities Higher with New 320GB Travelstar Hard Drives
Achieves over 140 million accumulative media shipment since establishment in 1998
- Bolstering Hitachi’s position as the segment and technology leader in 2.5-inch hard drives, the company announced volume shipment of new 5,400 RPM notebook hard drives with a maximum available capacity of 320GB. Designed to support the multi-tasking needs of consumers and commercial users balancing mobile computing and movies, music, photos and games on-the-go, the Travelstar™ 5K320 delivers the right capacity and performance options to meet the needs of IT and consumer electronics manufacturers. The new drives feature optional Bulk Data Encryption (BDE) for users requiring increased data security and enhanced availability models designed for use in 24x7 environments. Travelstar 5K320 delivers the performance needed for today’s advanced mobile applications. The drives’ Serial ATA (SATA) interface provides a fast 3Gb/s data transfer rate, allowing the drive to be used in a wide variety of applications including mainstream computing, portable external storage devices, small form factor video devices, game consoles and other advanced mobile devices.

The Travelstar 5K320 elevates the standard for hard drive reliability with design enhancements that include altitude-sensing Thermal Fly-height Control (TFC), an improved actuator latch and fourth generation perpendicular magnetic recording (PMR) head technology. These features combine to safeguard user data that might otherwise be compromised as a result of accidental falls, bumps and rough handling. The drives also include TrueTrack™ technology, which improves tracking accuracy in high shock or vibration environments. These features combine to deliver an industry-leading 400Gs of operating shock protection. The Travelstar 5K320 does not sacrifice performance in its quest to be energy efficient. The drives only consume 1.8W of power when reading and writing and their .55W low power idle means longer battery life for more “unplugged” notebook time and a longer drive life expectancy.
“The Travelstar 5K320 addresses a growing demand for high capacity hard drives, which are at the heart of today’s notebook PCs, external storage devices, gaming consoles and other mobile computing applications,” said Larry Swezey, director, Consumer and Commercial HDD, Hitachi Global Storage Technologies. “And when coupled with our optional Bulk Data Encryption technology, the Travelstar 5K320 offers even greater value to notebook users by helping to guard against data theft.” The Travelstar 5K320 is available in single or dual-platter configurations with capacities between 80GB and 320GB. The 320GB version can hold up to 320 hours of digital video, 160 PC computer games or 80,000 four-minute songs. Hitachi will also offer an enhanced-availability (EA) version of the drive that is designed for applications requiring 24x7 operation in lower transaction environments, such as blade servers, network routers, point-of-sale terminals and video surveillance systems.




Bulk Data Encryption

The Travelstar 5K320 features optional Bulk Data Encryption (BDE) for hard-drive-level data security. Previously, data on a hard drive could be protected either through software-based encryption or a system-level password. However, hard-drive-level encryption provides improved performance and a higher level of security than any of the previously available options. Hitachi and Phoenix Technologies (Nasdaq: PTEC) recently announced a collaboration to provide next-generation mobile PC security on notebooks equipped with Hitachi hard drives. When the Travelstar 5K320 is installed in a notebook using the Phoenix FailSafe™ theft-deterrence service, PC owners can track, remotely disable and securely erase the hard drive. As a result, vital data stored on the notebook remains safe and protected. Hitachi’s encryption technology combined with Phoenix’s FailSafe technology forms the core of this innovative security solution.

Technical Specifications:
Travelstar 5K320
320/250/160/120/80 GB
9.5 mm in height
5400 RPM
250 billion bits per square inch maximum areal density
2/2/1/1/1glass disk platter (s)
4/3/2/2/1 TMR recording head(s)
1000 G/1ms non-operating shock
400 G/2ms operating shock
5.5 ms average latency
12 ms average read time
0.8W active idle
0.55W low-power idle
Serial ATA 3.0Gb/s, 1.5Gb/s encrypted
102//95 grams in weight
2.4 Bels typical idle acoustics
2.6 Bels typical operational acoustics


Availability

The Travelstar 5K320 is now shipping to customers worldwide. The enhanced-availability version of the drive is expected to ship in the second quarter of 2008.

[freeek]

SATA


Features

The current SATA specification can support data transfer rates as high as 3.0 Gbit/sec per device. SATA uses only 4 signal lines; cables are more compact and cheaper than for PATA. SATA supports hot-swapping and NCQ. 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.


Throughput

SATA 1.5 Gbit/s
First-generation SATA interfaces, also known as SATA/150 or unofficially as SATA 1, communicate at a rate of 1.5 gigabits per second (Gbit/s). Taking into account 8b10b coding overhead, the actual uncoded transfer-rate is 1.2 Gbit/s, or 1,200 megabits per second (Mb/s). The theoretical burst throughput of SATA/150 is similar to that of PATA/133, but newer SATA devices offer enhancements such as NCQ which improve performance in a multitasking environment. Data transfer rates are limited by mechanical hard drives themselves, not the interfaces: the fastest modern desktop hard drives transfer data at a maximum of about 120 MB/s,[2] which is well within the capabilities of even the older PATA/133 specification.

During the initial period after SATA/150's finalization adapter and drive manufacturers used a "bridge chip" to convert existing PATA designs for use with the SATA interface.[citation needed] Bridged drives have a SATA connector, may include either or both kinds of power connectors, and generally perform identically to their PATA equivalents. Most lack support for some SATA-specific features such as NCQ. Bridged products gradually gave way to native SATA products.


SATA 3.0 Gbit/s
Soon after SATA/150's introduction a number of shortcomings were observed. At the application level SATA could only handle one pending transaction at a time, like PATA; the SCSI interface has long been able to accept multiple outstanding requests and service them in the order which minimises response time. This feature, Native Command Queuing (NCQ), was adopted as an optional supported feature for SATA 1.5 Gbit/s and SATA 3.0 Gbit/s devices.

First-generation SATA devices were at best little faster than parallel ATA/133 devices. A 3 Gbit/s signaling rate was added to the Physical layer (PHY layer), effectively doubling maximum data throughput from 150 MB/s to 300 MB/s. SATA/300's transfer rate is expected to satisfy drive throughput requirements for some time, as the fastest desktop hard disks barely saturate a SATA/150 link. A SATA data cable rated for 1.5 Gbit/s will handle current second-generation SATA 3.0 Gbit/s drives without any loss of sustained and burst data transfer performance.

Backward compatibility between SATA 1.5 Gbit/s controllers and SATA 3.0 Gbit/s devices was important, so SATA/300's autonegotiation sequence is designed to fall back to SATA/150 speed (1.5 Gbit/s rate) when in communication with such devices. In practice, some older SATA controllers do not properly implement SATA speed negotiation. Affected systems require the user to set the SATA 3.0 Gbit/s peripherals to 1.5 Gbit/s mode, generally through the use of a jumper.[3] Chipsets known to have this fault include the VIA VT8237 and VT8237R south bridges, and the VIA VT6420 and VT6421L standalone SATA controllers.[4] SiS's 760 and 964 chipsets also initially exhibited this problem, though it can be rectified with an updated SATA controller ROM.




SATA II Misnomer
The 3.0 Gbit/s specification has been widely referred to as "Serial ATA II" ("SATA II" or "SATA2"), contrary to the wishes of the Serial ATA International Organization (SATA-IO) which defines the standard. SATA II was originally the name of a committee defining updated SATA standards, of which the 3 Gb/s standard was just one. However since it was among the most prominent features defined by the former SATA II committee, the name SATA II became synonymous with the 3 Gb/s standard, so the group has since changed names to the Serial ATA International Organization, or SATA-IO, to avoid further confusion.


SATA 6.0 Gbit/s
SATA's roadmap includes plans for a 6.0 Gbit/s standard. In current PCs, SATA 3.0 Gbit/s already greatly exceeds the sustainable (non-burst) transfer rate of even the fastest hard disks. The 6.0 Gbit/s standard is useful right now 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.[5] Solid-state drives such as RAM disks may also one day make use of the faster transfer rate.


Cables and connectors
Connectors and cables are the most visible difference between SATA and Parallel ATA 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 adapters.





A 7-pin Serial ATA data cable.
The SATA standard defines a data cable with seven conductors (3 grounds and 4 active data lines in two pairs) and 8 mm wide wafer connectors on each end. SATA cables can be up to 1 m (39 in) long, and connect one motherboard socket to one hard drive. PATA ribbon cables, in comparison, connect one motherboard socket to up to two hard drives, carry either 40- or 80-conductor wires, and are limited to 45 cm (18 in) in length by the PATA specification (however, cables up to 90 cm (36 in) are readily available). Thus, SATA connectors and cables are easier to fit in closed spaces and reduce obstructions to air cooling. They are more susceptible to accidental unplugging, but cables can be purchased that have a 'locking' feature, whereby a small (usually metal) spring holds the plug in the socket.

Parallel ATA uses single ended signalling. In this system, the noise is amplified with the data signal during the signal transmission. Noise causes significant interference with the data signal at higher speeds. In order to reduce the noise interference, the driving voltage of Parallel ATA is as high as 5V. Although the higher voltage can reduce the noise interference, the 5V is too high for modern high speed silicon devices. Thus the fabrication cost of driving ICs is higher, and the speed is limited in comparison to low voltage silicon ICs.

In comparison, SATA systems use differential signalling. In this system, it is easy to filter out the noise from data signal during the signal transmission. The higher noise rejection allows the SATA system to use only 500mV peak-to-peak differential voltage to carry the signal at higher speeds without distortion or noise interference.

Compared with the 5V driving voltage in PATA ribbon cables, the 0.5V in SATA cables make the SATA system much more power efficient.

Power



A 15-pin Serial ATA power connector.
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. Native SATA devices favor the SATA power-connector over the old four-pin Molex connector (found on all PATA equipment), although some SATA drives retain older 4-pin Molex. The SATA/power connector has been criticized for its poor robustness[citation needed]—the thin plastic tops of the connectors (see power connector picture at left) can break due to shearing force when the user pulls the plug at a non-orthogonal angle. The seemingly large number of pins are used to supply three different voltages: 3.3 V, 5 V, and 12 V. Each voltage is supplied by three pins ganged together, while ground is provided by five pins. Each pin should be able to provide 1.5 A. Pin 11 is used in newer drives for staggered spinup. The supply pins are ganged together because the small pins by themselves cannot supply sufficient current for some devices. One pin from each of the three voltages is also used for hotplugging.

Adaptors are available to convert a 4-pin Molex connector to SATA power connector. However, because the 4-pin Molex connectors do not provide 3.3 V power, these adapters provide only 5 V and 12 V power and leave the 3.3 V lines disconnected. This precludes the use of such adapters with drives that require 3.3 V power. Understanding this, drive manufacturers have largely left the 3.3 V power lines unused. However, without 3.3 V power, the SATA device may not be able to implement hotplugging as mentioned in the previous paragraph. Other adapters produce 3.3V from the 5V line using a resistor or other means to reduce the voltage.


External SATA

The official eSATA logoStandardized in mid-2004, 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 2 m (USB and FireWire allow longer distances.)
The external cable connector is a shielded version of the connector specified in SATA 1.0a with these basic differences:
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 further 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 five.

SATA (left) and eSATA (right) connectors

Aimed at the consumer market, eSATA enters an external storage market already served by the USB and FireWire interfaces. Most external hard disk drive cases with FireWire or USB interfaces use either PATA or SATA drives and "bridges" to translate between the drives' interfaces and the enclosures' external ports, and this bridging incurs some inefficiency. Some single disks can transfer almost 120 MB/s during real use,[2] more than twice the maximum transfer rate of USB 2.0 or FireWire 400 (IEEE 1394a) and well in excess of the maximum transfer rate of FireWire 800, though the S3200 FireWire 1394b spec reaches ~400 MB/s. Finally, some low-level drive features, such as S.M.A.R.T., may not be available through USB or FireWire bridging.[6] eSATA does not suffer from these issues.


HDMI, Ethernet, and eSATA ports on a Sky HD DigiboxIt is likely that eSATA co-exist with USB 2.0 and FireWire external storage for several reasons. As of early 2008 the vast majority of mass-market computers have USB ports and many computers and consumer electronic appliances have FireWire ports, but few devices have external SATA connectors. For small form-factor devices (such as external 2.5" (70 mm) disks), a PC-hosted USB or FireWire link supplies sufficient power to operate the device. Where a PC-hosted port is concerned, eSATA connectors cannot supply power, and would therefore be more cumbersome to use.

As of 2007, an eSATA external drive enclosure will typically ship with a passive eSATA-to-SATA bracket/cable-adapter to install on desktops that lack an eSATA port or that need another. Desktops can also be upgraded with the installation of an eSATA host bus adapter (HBA), while notebooks can be upgraded with Cardbus[7] or ExpressCard[8] versions of an eSATA HBA. With passive adapters the maximum cable length is reduced to 1 meter due to the absence of compliant eSATA signal levels. Full SATA speed for external disks (115 MB/s) have been measured with external RAID enclosures

From the second half of 2008, SATA-IO expects eSATA to provide power to eSATA devices without the need for a separate power connection. In a news release from 2008-01-14, SATA-IO calls it the "Power Over eSATA initiative."

eSATA may be of interest to the enterprise and server market, which has already standardized on the Serial Attached SCSI (SAS) interface, because of its hotplug capability and low price .

Note: Prior to the final eSATA specification, there were a number of products designed for external connections of SATA drives. Some of these use the internal SATA connector or even connectors designed for other interface specifications, such as FireWire. These products are not eSATA compliant. The final eSATA specification features a specific connector designed for rough handling, similar to the regular SATA connector, but with reinforcements in both the male and female sides, inspired by the USB connector. It's harder to unplug, and can withstand yanking or wiggling which would break a male SATA connector (the hard drive or host adapter, usually fitted inside the computer). With an eSATA connector considerably more force is needed to damage the connector, and if it does break it is likely to be the female side, on the cable itself, which is relatively easy to replace.[citation needed]


Topology

SATA topology: host – expansor - deviceSATA is a point to point architecture. The connection between the controller and the storage device is direct.

In a modern PC system, the SATA controller is usually found on the motherboard, or installed in a PCI slot. Some SATA controllers have multiple SATA ports and can be connected to multiple storage devices. There are also port expanders which allow multiple storage devices to be connected to a single SATA controller port.


Encoding
These high-speed transmission protocols use a logic encoding known as 8b10b. The signal is sent using Non-return to Zero (NRZ) encoding with Low Voltage Differential Signaling (LVDS).

In the 8b10b encoding the synchronizing signal is included in the data sequence. This technique is known as Clock Data Recovery, because it doesn't use separate synchronizing signal, instead utilizing the serial signal's 0 to 1 transitions to recover the clock signal.


Backward and forward compatibility
SATA and PATA
At the device level, SATA and PATA devices are completely incompatible—they cannot be interconnected. At the application level, SATA devices are specified to look and act like PATA devices.[9] In early motherboard implementations of SATA, backward compatibility allowed SATA drives to be used as drop-in replacements for PATA drives, even without native (driver-level) support at the operating system level.

The common heritage of the ATA command set has enabled the proliferation of low-cost PATA to SATA bridge-chips. Bridge chips were widely used on PATA drives (before the completion of native SATA drives) as well as standalone ‘dongles’. When attached to a PATA drive, a device-side dongle allows the PATA drive to function as a SATA drive. Host-side dongles allow a motherboard PATA port to function as a SATA host port.

Powered enclosures are available for both PATA and SATA drives, which interface to the PC through USB, Firewire or eSATA, with the restrictions noted above. PCI cards with a SATA connector exist that allow SATA drives to connect to legacy systems without SATA connectors.


SATA 1.5Gb/s and SATA 3Gb/s
SATA is designed to be backward and forward compatible with future revisions of the SATA standard.

According to the hard drive manufacturer Maxtor, motherboard host controllers using the VIA and SIS chipsets VT8237, VT8237R, VT6420, VT6421L, SIS760, SIS964 found on the ECS 755-A2 which was manufactured in 2003, do not support SATA 3Gb/s drives. To address interoperability problems, the largest hard drive manufacturer Seagate/Maxtor have added a user-accessible jumper-switch known as the Force 150, to switch between 150 MB/s and 300 MB/s operation.[3] Users with a SATA 1.5Gb/s motherboard with one of the listed chipsets should either buy an ordinary SATA 1.5Gb/s hard disk, buy a SATA 3Gb/s hard disk with the user-accessible jumper, or buy a PCI or PCI-E card to add full SATA 3Gb/s capability and compatibility. Western Digital uses jumper setting called "OPT1 Enabled" to force 150 MB/s data transfer speed.


Comparisons with other interfaces

SATA and SCSI
SCSI currently offers transfer rates higher than SATA, but is a more complex bus usually resulting in higher manufacturing cost. Some drive manufacturers offer longer warranties for SCSI devices, however, indicating a possibly higher manufacturing quality control of SCSI devices compared to PATA/SATA devices. SCSI buses also allow connection of several drives (using multiple channels, 7 or 15 on each channel), whereas SATA allows one drive per channel, unless using a port multiplier.

SATA 3.0 Gbit/s offers a maximum bandwidth of 300 MB/s per device compared to SCSI with a maximum of 320 MB/s. Also, SCSI drives provide greater sustained throughput than SATA drives because of disconnect-reconnect and aggregating performance. SATA devices are generally compatible with SAS enclosures and adapters, while SCSI devices cannot be directly connected to a SATA bus.

SCSI, SAS and FC drives are typically more expensive so they are traditionally used in servers and disk arrays where the added cost is justifiable. Inexpensive ATA and SATA drives evolved in the home computer market, hence the general opinion is that they are less reliable. As those two worlds started to overlap, the subject of reliability became somewhat controversial. It is worth noting that generally a disk drive has a low failure rate because of increased quality of its heads, platters and supporting manufacturing processes, not because of having a certain interface.

Unlike PATA, both SATA and eSATA are designed to support hot-swapping. However, this feature requires proper support at the host, device (drive), and operating-system level. In general, all SATA/devices (drives) support hot-swapping (due to the requirements on the device-side), but requisite support is less common on SATA host adapters.[citation needed]

USB allows hot-swapping; this is supported by virtually every current operating system. However, USB-based storage hardware can infrequently sustain data loss when disconnected. This problem exists with media players and digital cameras using flash memory as well as mobile 2.5-inch USB hard drives.[citation needed] Firmware damage and data loss can occasionally result from unclean spin-downs and power loss when the drive or device is removed from the USB port without first initiating a device shutdown via the computer's operating system.[16]

SCSI devices with SCA-2 connectors are designed for hot-swapping. Many server and RAID systems provide hardware support for transparent hot-swapping. The SCSI standard prior to SCA-2 connectors was not designed for hot-swapping, but, in practice, most RAID implementations support hot-swapping of hard disks.

Serial Attached SCSI (SAS) is designed for swapping

[Style Mantra]

nice info freeek

[Admin]

nice information.