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December 11, 2001

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Easily Add SCSI to Laptop, Notebook, & Desktop Computers

Belkin USB SCSI Adapter - Back and Front Views.

Article Index

USB & SCSI Data Speeds

Necessity -- No Card Slot

Necessity -- No IRQ

Convenience

Cautions & Annoyances

System Requirements

Conclusion

How We Used & Tested the Adapter

Resources

Belkin SCSI to USB Adapter

for Mac & Windows

By Mike Angelo - 11 December 2001 (c)

Do you have an external SCSI device but no SCSI adapter, e.g. a laptop or notebook computer? Or, do you have an external SCSI device but you are out of available IRQs or expansion slots to use for a SCSI adapter? If so, in the toys-for-girls-and-boys department Belkin has a handy solution for you.

The Belkin USB SCSI Adapter with Termpower ($99.95) let's you connect an external SCSI (Small Computer System Interface) device such as a CD-ROM drive, CD-Burner, Scanner, Zip Drive, Printer, and so forth to your computer via its Universal Serial Bus (USB). The USB to SCSI Adapter trick is for convenience or necessity -- not for speed.

About USB & SCSI Data Speeds

You will loose much of the speed of SCSI devices by connecting them to your computer via the USB. The maximum USB 1 transfer speed is 1.5 MBps (MegaBytes per second). You might see the max USB 1 speed listed as 12-Mbps (Megabits per second) some places. If you do the math, 12-Mbps should translate to 1.5-MBps.

Regular SCSI throughput speeds range from 4-MBps up to 320-MBps. Thus, pushing the SCSI signal into a USB signal knocks the maximum possible data transfer rate in a SCSI-USB paradigm down to the limiting USB 1.5 MBps rate. Incidentally, max CD burn speed using the SCSI to USB adapter is 4x.

A SCSI to USB adapter implementing the newer USB 2 specification would provide a much faster SCSI-USB maximum throughput. However, we do not know of any USB 2 devices that adapt SCSI to USB, which are available at this time. USB 2 provides a maximum data transfer speed of 60-MBps -- forty times the speed of USB 1.

The slowest SCSI throughput rate standard is 4-MBps, which is the original SCSI-1 specification. SCSI throughput can be as fast as 320-MBps under the SCSI-3 Ultra4 SCSI standard. Even the oldest and slowest SCSI transfer rate of 4-MBps is substantially faster than the max 1.5-MBps SCSI transfer speed via the USB 1 connection. The USB 1 to SCSI Adapter trick is for convenience or necessity -- not for speed.

Necessity -- No Card Slot

The PowerLeap-based machine we tested the SCSI to USB adapter on is a good example of necessity. It's a powerful, multi-boot, machine with a 1-GHz Pentium III CPU on a PowerLeap motherboard using a SiS 630E chipset with integrated everything, 512-MB of PC-100 RAM, and a 100-GB Maxtor D536X hard drive -- all in a generic ATX case. Unfortunately, it has no expansion card slots and it has no SCSI connections.

The PowerLeap motherboard is a large AT expansion card without edge contacts. The card has the edge, just not the contacts. All the motherboard chips, connectors, sockets, gizmos, gadgets, widgets, and so forth are on the PowerLeap motherboard. The particularly neat concept of the PowerLeap motherboard is that it lets you upgrade an older computer without ever having to remove the old motherboard or anything else for that matter. The old motherboard serves merely as a holder for the new PowerLeap board. That is why there are no contacts on the card's edge..

You simply drop the PowerLeap motherboard into an AT slot on the old motherboard, move the power connectors to the PowerLeap motherboard, reconnect the drive signal cables to the PowerLeap motherboard, do a few more minor housekeeping chores, and voila you are up and running. All in all, it is a pretty slick concept.

However, thanks to the SCSI to USB adapter, attaching an external SCSI CD-RW drive to the PowerLeap machine was as simple as plugging the CD burner into the SCSI to USB adapter and then plugging the adapter into one of the PowerLeap box's USB connectors. After that, it was a simple, straightforward, driver installation. All the installation stuff was on a CD-ROM that came with the SCSI to USB adapter.

Of course you do not get the benefits of the native SCSI speed that you would have if you used a regular SCSI adapter card. But without the SCSI to USB adapter you would not be able to connect your external SCSI devices to a computer that does not have a slot in which to install a SCSI adapter card.

Laptop and notebook computers are another example of using a SCSI to USB adapter as a matter of necessity. Most if not all laptop or notebook computers do not come with SCSI support. However, most if not all laptop or notebook computers come with USB capability these days.

SCSI PC Cards are available. However, an advantage of a SCSI to USB adapter is that you can use it with either laptop or desktop computers. Also, using the SCSI to USB adapter does not require a unique IRQ for your SCSI device(s).

Necessity -- No IRQ

Perhaps your computer has an available expansion card slot and does not have a SCSI adapter card already installed. Suppose, however, that even though your computer has an available expansion slot for a SCSI card all the IRQs (Interrupt Requests) are used.

All the devices connected to a USB port share the IRQ assigned to the USB port. That means that you can connect a SCSI device to your computer via the SCSI to USB adapter -- without the need to use a separate IRQ for the SCSI device.

You avoid the need to use a separate IRQ for an external SCSI device when you attach that SCSI device to your computer by using the SCSI to USB adapter. Here you trade SCSI performance for an IRQ by using the SCSI-USB adapter rather than by using a regular SCSI adapter card.

Convenience

Suppose your computer has an available expansion card slot and does not have a SCSI adapter card already installed. Even if your computer has an available expansion slot for a SCSI card you avoid the need to pop the top and install a SCSI adapter card in the computer by using the SCSI to USB adapter.

Here again, there is a trade-off between ease, convenience, and simplicity with the SCSI to USB adapter verses the better overall performance of a regular SCSI adapter card in the computer. If you are a more experienced computer user then you might prefer to install a regular, internal, SCSI adapter card to achieve full SCSI performance. However, if you are less experienced with installing devices or upgrading your computer, you might prefer the easier, SCSI to USB adapter.

Cautions & Annoyances

If you are in the habit of hot-swapping USB devices, you often cannot do that with the SCSI to USB adapter. Disconnecting the external SCSI device connected to your computer via the SCSI to USB adapter while your computer is running might cause the computer to lock badly enough that you will have to re-boot.

If you have several USB devices plus the SCSI to USB adapter you might consider using a USB hub. That way, you will not have to unplug the SCSI to USB adapter to plug in another USB device.

There are exceptions. One computer we used to test the Belkin USB SCSI adapter is an HP Omnibook 6000 notebook computer running Windows 2000. It has a nifty Unplug or Eject Hardware feature. Using the Unplug or Eject Hardware feature to remove the Belkin USB SCSI adapter allowed us to hot-swap the external SCSI CD-burner we used in out tests without any lockups.

The SCSI connector on the Belkin USB SCSI Adapter is a DB25 female. However, there is an assortment of connectors used by SCSI devices. If you want to use the Belkin USB SCSI Adapter with a SCSI device that does not use a DB25 connector, please check to make sure you can get the appropriate SCSI-to-SCSI adapter.

Not all external SCSI devices are compatible with the Belkin USB SCSI Adapter. Before you order a Belkin USB SCSI Adapter you should check the compatibility list to make sure your external SCSI device will work with the Belkin USB SCSI Adapter. If your external device is not on the compatibility list, give Belkin a call to see if your SCSI device might work with the Belkin USB SCSI Adapter even though it is not on the compatibility list.

System Requirements for the Belkin F5U115-UNV USB SCSI Adapter

The Belkin F5U115-UNV USB SCSI Adapter requires a PC or PC compatible computer or a Macintosh computer with a free USB port. For the PC, you will need to be running Windows 98, Windows ME, Windows XP, or Windows 2000. Unfortunately Belkin does not provide Linux support for its USB SCSI Adapter -- nor were we able to find any third party Linux drivers for it.

With some SCSI devices you might need to buy the optional Belkin F5U115xPWR power supply for the Belkin F5U115-UNV USB SCSI Adapter. Also, if your SCSI device does have a cable with a free male DB25 connector, you might need to obtain an additional SCSI cable(s) or SCSI-SCSI adapter(s) in order to connect your SCSI device to the Belkin F5U115-UNV USB SCSI Adapter.

You also should check the compatibility list (link in the Resources section below) or check with Belkin if your SCSI device is not on the compatibility list to make sure your SCSI device will work with the Belkin USB SCSI Adapter.

Conclusion

Are you one of those people with several computers on your desk that is suffering from desktop clutter -- are too many mice and keyboards getting in the way? Or do you have only one printer or other such peripheral device that you would like to share among several computers? Also, in the toys-for-girls-and-boys department Belkin has a nifty solution for Linux, Mac, and Windows users -- the Belkin USB Switch.

The Belkin F5U115-UNV USB SCSI Adapter is a clever and handy computer accessory for connecting an external SCSI device such as an external CD-ROM or hard drive, Scanner, Zip Drive, Printer, and so forth to your computer via its Universal Serial Bus. It's easy to install.

The Belkin USB SCSI Adapter provides an easy way to add SCSI functionality to your PC. Moreover, it lets you connect an external SCSI device to a computer that does not support SCSI but does have a USB port -- such as a typical laptop or notebook computer.

On the downside, the USB 1 data transfer speed is much slower than SCSI data transfer speeds. So, you lose the native speed performance of the SCSI device by using the USB SCSI Adapter to connect it to your computer, rather than by using a standard SCSI adapter card to make the connection.

Nevertheless, where you cannot use a standard SCSI adapter card to connect an external SCSI device to your computer, you easily can connect that external SCSI device to your computer by using the Belkin USB SCSI Adapter. Or, if you just do not want the hassle of installing a SCSI adapter card inside of your computer, the USB SCSI Adapter provides a very convenient way of using an external SCSI device with your computer.

How We Used & Tested the Belkin USB SCSI Adapter

Here is what we did to test the Belkin F5U115-UNV USB SCSI Adapter. After installing the USB SCSI Adapter to each of two computers, we connected the USB SCSI Adapter to a Ricoh MediaMaster MP 6200S external SCSI CD-burner. (One computer at a time, of course.) Then we used the Ricoh MediaMaster connected to the computer via the Belkin USB SCSI Adapter as a CD reader for several days on each computer.

Next we installed Adaptec's Easy CD Creator 4 to check the Belkin USB SCSI Adapter's performance when burning CDs. We ran the battery of system tests that are part of the Easy CD Creator software on the Ricoh MediaMaster and Belkin USB SCSI Adapter setup. The SCSI-USB setup passed all tests.

The Ricoh MediaMaster MP 6200S external SCSI CD-RW was used for the CD burn checks. The MP 6200S burns CD-R and CD-RW media at a maximum 2X burn speed, which is the burn rate we used in our tests.

Easy CD Creator is good, popular CD-burning software. Incidentally, Easy CD Creator now is a Roxio product and the current version is Easy CD Creator 5.

Everything worked fine. More importantly we did not end up with any coasters/frisbees.

The desktop computer used is a powerful, multi-boot, machine running Microsoft Windows 98 SE. It has a 1-GHz Pentium III CPU, PowerLeap Renaissance/370S motherboard using a SiS 630E chipset with integrated everything except SCSI, 512-MB of PC-100 RAM, and a 100-GB Maxtor D536X hard drive in a generic ATX case.

The laptop used is a Hewlett Packard OmniBook 6000 Notebook PC running Microsoft Windows 2000. This HP 6000 has a 900-MHz Pentium III CPU, 128-MB RAM, ATI Rage Mobility M1 graphics, and a 20-GB IBM DJSA-220 hard drive.

We did not check the Belkin USB SCSI Adapter on a Macintosh.