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SATA

Penelope Truce
Penelope Truce
Sep 28, 2009
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SATA:

 

In computer hardware, Serial ATA is a computer bus technology primarily designed for transfer of data to and from hard disks and optical drives. It was designed as a successor to the legacy Advanced Technology Attachment standard (ATA). Serial ATA adapters and devices communicate over a high-speed serial link.

SATA is a modern, high-speed data storage interface which integrates the device controller on the disk drive itself. It supports only single drive per cable configurations. By removing the drive controller functions from the Personal Computer (PC) system board, much of the workload of reading and writing data is off-loaded to the disk drive, freeing up resources on the system board. Limiting the number of drives to one per cable also helps with performance. SATA drives do not have to share connection bandwidth with peer drives.

 

Sata Architechture:

At the physical layer of the Serial ATA architecture, the data-connection is formed by two pairs of (unidirectional) signal wires. Over these wires, SATA uses Low Voltage Differential Signaling (LVDS), enabling much higher (per-wire) signaling rates (1.5 Gbit/s and up) than traditional parallel ATA. Byte data is encoded and transmitted using 8B/10B encoding, which is also used in Ethernet, Fiber Channel, PCI Express, etc. This encoding scheme has an efficiency of 80%, but the 8B/10B encoding embeds the information necessary to distinguish bit and character boundaries, eliminating the need for a separate clock signal. Above the SATA physical level is the link level and transport level. These higher levels convert configuration and data-operations into discrete ordered packets, for transmission over the SATA link. At the application level, SATA inherits ATA's operational model, with the 'task register file' (for generating read/write PIO and DMA requests) a mandatory part of all SATA host implementations. Each SATA/device has a link to a SATA host-port, with no sharing of cable or bandwidth between devices.

The SATA standard defines a data cable using seven conductors (of which 4 are active data lines) and 8 mm wide wafer connectors on each end.

 

Serial interface:

Serial interfaces transfer data in single-bit streams. This differs from parallel interfaces which transmit multiple bits simultaneously. Serial interfaces do not suffer the controller over-head of managing multi-bit communication required for parallel communication. This allows SATA drives to transmit data at much higher rates than older Parallel Advanced Technology Attachment (PATA) drives. SATA has a specified maximum cable length of 1 meter.

 

SCSI

 

SCSI  is a family of parallel interface standards used for attaching peripheral devices to computers. They support up to 15 peripheral devices attached to one data bus at a time.

SCSI supports attaching multiple physical devices to a single data bus. There are single-channel, dual-channel and quad-channel SCSI Host Bus Adapters (HBA) available. Computers can therefore have one, two or four busses to which peripherals can be attached.

 

8-bit SCSI devices support a maximum of 8 devices (ID's 0-7) and 16-bit SCSI devices support a maximum of 16 devices (ID's 0-15). The SCSI controller, using a standard default configuration, is assigned ID 7. Therefore, with 8-bit SCSI, up to 7 additional peripherals can be added to the bus and with 16-bit SCSI up to 15 additional peripherals can be added to the bus.

 

Communication on a SCSI bus requires proper termination. The terminator prevents the transmitted signals from echoing on the bus. The last device on the bus (the one furthest from the HBA) provides the termination. Older SCSI busses were terminated with special cable terminator plugs. More recent SCSI devices can be set to provide internal termination (set to disabled for all but the last device with has internal termination enabled). Very modern devices can auto-detect whether or not they are the terminating device and can configure themselves accordingly.

 

Parallel data transfer in Hard disk:

 

A dual actuator arm assembly system uses two pairs of actuator-carriage arms that linearly move over a stationary micro-rail independently. The geometric shape of the two pairs of actuator carriage arms conform to the arcs of the data tracks at an acute angle. System enables micro-actuation that is integrated to actuator arm and is a function of its geometry. Uninterrupted data stream and sector coverage and thus parallel data transfer scheme is made possible. Each actuator move only within a limited range of disk area, thus precision is increased, vibration is minimized and external transfer rate is speeded up and overall access time is shortened. Instant access to two quarters of the disk with two pairs of actuators and to park these without landing the heads--by positioning and constant fly height during idle mode, or when system is turned off, are introduced as what are new in the art.

 

Parallel data transfer in Floppy disk:

 

The ST-506/412 interface was developed by Seagate Technology, Inc. It's the interface used to control most floppy disk drives in use today. This is one of the interfaces where most of the electronics is actually on a controller card mounted in the host computer. With this interface, the controller card does most of the work (moving the magnetic head, spinning the disk, etc.). The controller card also cleans any data coming from the disk drive by stripping off the formatting and control signals that were used to store the data onto the hard disk. A hard disk drive is connected to the controller card in the host computer via two ribbon cables (a 34-pin control cable and a 20-pin data cable). Floppy drives use only the 34-pin control cable to transfer both data and control signals. The transfer rate of this interface is 5-Mbits per second.

Author's note: SATA
Keywords: SATA



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