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eSATA vs IE1394a/b vs USB 2.0

Discussão em 'Digital Life' iniciada por PsySc0rpi0n, 1 de Dezembro de 2008. (Respostas: 0; Visualizações: 5279)

  1. PsySc0rpi0n

    PsySc0rpi0n Power Member


    Comparison to USB

    Although high-speed USB 2.0 runs at a higher signaling rate (480 *****/s) than FireWire 400, typical USB PC-hosts rarely exceed sustained transfers of 35 MB/s (280 Mb/s), with 30 MB/s (240 Mb/s) being more typical (the theoretical limit for a USB 2 high-speed bulk transfer is 53.125 MB/s). This is likely due to USB's reliance on the host-processor to manage low-level USB protocol, whereas FireWire automates the same tasks in the interface hardware. For example, the FireWire host interface supports memory-mapped devices, which allows high-level protocols to run without loading the host CPU with interrupts and buffer-copy operations.
    FireWire 800 is substantially faster than Hi-Speed USB.



    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, 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., are not usable through USB or FireWire bridging. eSATA does not suffer from these issues.

    eSATA will likely co-exist alongside USB 2.0 and FireWire storage for several reasons. The ubiquity of USB ports on all mass-market computers, and FireWire ports on many consumer electronic appliances, guarantee a large market for USB and FireWire storage. 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 or ExpressCard 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.


    FireWire 1394a/b

    Enhancements (IEEE 1394a-2000)

    An amendment IEEE 1394a was released in 2000, which both clarified and enhanced the original specification. It added in support for asynchronous streaming, quicker bus reconfiguration, packet concatenation, and a power saving suspend mode.
    1394a also standardized the 4-circuit alpha connector developed by Sony and already widely in use. The 4-circuit version is used on many consumer devices such as camcorders, laptops, and other small FireWire devices. Though fully data compatible with 6-circuit alpha interfaces, it lacks power connectors.

    FireWire 800 (IEEE 1394b-2002)

    IEEE 1394b-2002 introduced FireWire 800 (Apple's name for the 9-circuit "S800 bilingual" version of the IEEE 1394b standard) This specification and corresponding products allow a transfer rate of 786.432 *****/s full-duplex via a new encoding scheme termed beta mode. It is backwards compatible to the slower rates and 6-circuit alpha connectors of FireWire 400. However, while the IEEE 1394a and IEEE 1394b standards are compatible, FireWire 800's connector, referred to as a beta connector, is different from FireWire 400's alpha connectors, making legacy cables incompatible. A bilingual cable allows the connection of older devices to the newer port. In 2003, Apple was the first to introduce commercial products with the new connector.
    The full IEEE 1394b specification supports data rates up to 3200 *****/s over beta-mode or optical connections up to 100 metres in length. Standard Category 5e unshielded twisted pair supports 100 metres at S100. The original 1394 and 1394a standards used data/strobe (D/S) encoding (renamed to alpha mode) on the circuits, while 1394b adds a data encoding scheme called 8B10B referred to as beta mode.


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