SCSI v USB Scanners?

Discussion in 'Computer Information' started by John, Aug 2, 2004.

  1. John

    John Guest


    A lot of people seem to recommend SCSI connected scanners over USB
    ones, but isn't USB faster than SCSI?

    Maybe I'm wrong but I thought the speeds for the two standards were as

    USB2 480 Mbps
    SCSI-3 Ultra 20 MBps

    I thought that even USB 1 was 40 Mbps? So wouldn't that have been
    faster than the latest SCSI-3 Ultras speed can muster?

    Or perhaps the difference comes with the controllers and the SCSI just
    has better controllers and drivers, and the USB takes up too much
    resources? Or perhaps the USB can't achieve the top speeds it is
    supposed to be capable of, but the SCSI can?

    I'm a tad confused on this, but it does seem from what people say in
    comp.periphs.scanners that SCSI is faster?

    Thanks for any clarification on this

    John, Aug 2, 2004
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  2. Think you have megaBITS (Mb) and megaBYTES (MB) mixed here.
    Here's a pretty good chart of USB/SCSI/Firewire speeds:

    Few if any consumer grade scanners made with SCSI interface now anyway,
    so fairly moot, unless you're using older ones (like me)...

    Mac McDougald, Aug 2, 2004
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  3. The really important difference IMO is that SCSI peripherals are an
    utter pain in the backside to get working (and the pain increases as a
    high power of the number you daisy-chain), whereas every USB device I
    have ever used has connected and worked first time right out of the box.
    David Littlewood, Aug 2, 2004
  4. From John on 02/Aug/2004 00:12:
    Don't forget that to achieve 480Mbps, USB has to make very heavy use of the PC's
    CPU unlike SCSI and Firewire. This is probably OK for scanning but often
    catches people out for Video and other more intensive work.
    Julian Knight, Aug 2, 2004
  5. From Mac McDougald on 02/Aug/2004 00:55:
    Anyone had any joy with a SCSI->USB converter? I currently only have an ISA SCSI
    card which doesn't fit in my newer computers and was thinking this would be the
    best bet (avoiding the PCI/PCI Express/... issues altogether!).
    Julian Knight, Aug 2, 2004
  6. John

    Jim Berwick Guest

    What PCI/PCI Express issues?
    Jim Berwick, Aug 2, 2004
  7. John

    Glenn Guest

    USB definately uses a lot of CPU power. When I have my USB scanner
    driver GUI opened, CPU usage is 50% and CPU temps jump to about 50 C.

    Julian, are you looking for a PCI SCSI card? I have one just sitting
    here. I used it for optical drives, but I have gone IDE. I haven't
    used it since August 2002, I assume it works, it's been boxed up since then.
    Glenn, Aug 2, 2004
  8. John

    Thor Guest

    Don't forget that to achieve 480Mbps, USB has to make very heavy use of
    I think much depends on the USB chipset in particular, not necessarily the
    spec. I just transferred a 500MB file from my external hi-speed USB 2.0
    harddrive to my local harddrive, and my CPU utilization averaged around
    15-18% throughout. I'm using a USB 2.0 interface card with an NEC controller
    Thor, Aug 2, 2004
  9. John

    Ionizer Guest

    Spam report id 1151167261 sent to: abuse @
    Ionizer, Aug 2, 2004
  10. John

    David R Guest

    I have never had any problems with SCSI devices. My experiences have
    found them to be fast, reliable, and easy to configure. I've had
    drives and scanners running from Windows 98 to Windows XP.
    David R, Aug 2, 2004
  11. That's great; I wish you could share your secret. I have rarely been
    able to get two devices to work on the same chain, whatever combination
    of terminators/no terminators, permutations of device numbers etc. I

    Life is too short to waste on stuff like that...
    David Littlewood, Aug 2, 2004
  12. John

    RSD99 Guest

    SCSI is really quite easy to set up.

    (1) Put terminations on both of the *physical* ends of the transmission line(s). ONLY two
    terminations, one on each end. Usually, that will be (a) the adapter card, and (b) the
    last device on the chain. HOWEVER, if there are two cables coming out of the adapter, the
    adapter card should be unterminated, and the last device on each cable should be

    (2) Device #7 is the adapter card in the PC ... do not assign anything else to that number

    (3) EACH device on the SCSI chain needs a unique device number, make sure that there are
    no duplicated. That leaves Device numbers 0, 1, 2, 3, 4, 5, 6, and 7 for your devices. If
    you are setting up devices such as a scanner, try to steer clear of 0 and 1, which are
    normally used for disk drives.

    (4) If you are installing Hard Disks, 'Device 0' will be the boot drive.
    RSD99, Aug 3, 2004
  13. Did all this, in every permutation, with two different SCSI cards.

    I know quite a few other people who also find them a PITA.
    David Littlewood, Aug 3, 2004
  14. John

    R. P. Guest

    Firewire is as light on the CPU as SCSI? I had no idea. That's good
    to know when trying to decide what kind of external HD backup drive to
    get: USB-2 or Firewire.

    R. P., Aug 3, 2004
  15. From Jim Berwick on 02/Aug/2004 10:16:
    The fact that none of my PC's have PCI Express. If I upgrade to a motherboard
    with it, I will have to replace: Memory, Processor and power supply at the very
    least - again! If I don't replace, we are at the end of the line for PCI within
    a few years.

    If I choose USB it is likely to last another 10 years.
    Julian Knight, Aug 3, 2004
  16. From R. P. on 03/Aug/2004 07:15:
    One of the reasons that Firewire has been more expensive than USB.
    As someone pointed out though, perhaps some newer chipsets now don't need to hit
    the CPU as hard? However, the spec does allow it.
    Julian Knight, Aug 3, 2004
  17. From Glenn on 02/Aug/2004 14:47:
    Thanks Glenn, but as I said in my other post, I think I would rather choose a
    USB converter if I can simply for the flexibility (I can use it in any PC
    including my laptop and lend it to friends without having to trash their PCs)
    and the fact that I don't want to end up with another useless card when I next
    upgrade my desktop.

    I was interested though to here if anyone had used one of these converters,
    especially with scanners.
    Julian Knight, Aug 3, 2004
  18. John

    Bill Tuthill Guest

    Something worth reading (for laughs, if not actual insight) is the
    SCSI FAQ where FAQ means "facetiously" answered questions:

    The relevant part is, under Types of SCSI:

    3. Fast and loose SCSI. Often used in PCs. Has a few small variations
    from the official SCSI specification but works quite well as long as
    you never install new equipment or change the configuration.

    Another relevant part, and one reason SCSI has failed:

    In practice, SCSI-2 didn't work either. The industry's response to this
    was SCSI-3, which introduced thicker, sturdier, stronger, heavier, and
    far more expensive cables. [With 68 pins!]
    Bill Tuthill, Aug 4, 2004
  19. Bill, thanks for that, it gave me the best laugh so far this week. It
    actually sounds very close to my own experience of SCSI.

    David Littlewood, Aug 4, 2004
  20. John

    Glenn Guest

    I have an external firewire hard drive (internal in an enclosure), and
    it uses very little CPU while transferring files. I can only imagine
    what happens if I use the USB2.0 port instead.
    Glenn, Aug 4, 2004
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