Click for Mini Pro Dual Drive!
Click for Mini Pro Dual Drive!

Accelerate Your Mac!  - The source for Performance News and Reviews
The Source for Mac Performance News and Reviews
Don't forget to check out all the other site features!

Exclusive First Look: Adaptec 3950U2B
64-bit PCI Dual Channel Ultra2 SCSI controller for the B&W G3

Published: 4/17/99

card pix - click for larger  view

As reported at the main site news in mid April 1999, Adaptec has been shipping the 3950U2B 64-Bit PCI dual-channel Ultra2 SCSI controller to Apple for several weeks for use as an option at the Apple Store for dual channel Ultra2 SCSI option mac systems. I wanted to provide you with a sneak peek at what is without a doubt the most capable 'data pump' currently available (as of spring 1999) for a personal computer.

The Adaptec 3950U2B provides high bandwidth, dual-channel Ultra2 SCSI coupled to a 64-Bit PCI interface, making it an ideal card for high-performance servers and workstations. The two independent Ultra2 SCSI channels combine to provide a maximum data transfer rate of 160 MBytes/sec, 4 times that of a std UltraWide SCSI PCI Card. I'd love to see the rates possible with this card driving a 4 drive (or more) 10,000 RPM U2 RAID 0 array.

The real strength of this card would be shown in a configuration like a B&W G3 running OS X server, with adequate RAM (256MB or more) driving a Cheetah or IBM LXZ drive based RAID array on one channel and still having a dedicated 2nd channel for main file server use. Considering the capability this card provides, you'd have one very high performance web or file server, with none of the disk IO bottlenecks present in most current configurations.

With its 64-Bit PCI interface and dual, independent Ultra2 SCSI interfaces, the 3950 is a great slot saver with plenty of performance headroom for the future. I've bought more SCSI cards/flavors than I can count over the years, but owners of the 3950 should be set for the forseeable future.

performance chart  of SCSI interfaces

The 3950U2's 64-bit PCI bus interface (266MB/sec max) prevents the possibility of the PCI bus bottlenecking the dual Ultra2 SCSI channels (up to 160MB/sec), since standard 32-Bit PCI maxes out at 132MB/sec . (Note: Most pre-G3 Macs can't achieve the PCI maximum 132MB/sec rate however, due to PCI/Memory controller and system bus limits). The 3950U2B also works in non-B&W G3 systems, as the card is designed to be compabile with both 32-Bit and 64-Bit PCI interfaces. For best performance a 64-Bit PCI slot should be used, especially with mult-drive arrays.

3950U2B Features:

  • Up to 160 MByte/sec data transfer rate on two Ultra2 SCSI channels in a single 64-Bit PCI slot

  • 64-Bit PCI interface ensures bus bandwith exceeds maximum SCSI I/O rate

  • Connections for up to 30 SCSI devices

  • Advanced multimode I/O cell that accommodates either Ultra2 or legacy single-ended SCSI devices

  • Each of the two channels support up to 15 devices on a 12 meter cable

There is only one downside to the Mac 3950U2B - as I mentioned in the news a few weeks back, there are no plans for a retail version. It will only be available from the Apple Store as a BTO option (or a service part perhaps?). Perhaps Apple might consider offering it to existing B&W G3 owners as they did with the internal modems.

Although simple benchmarks do not begin to show the strengths of this card (Server applications with both channels running, 64-bit PCI bandwidth, etc.), preliminary tests with a Ultra2 SCSI Seagate Cheetah 4.5 GB and Quantum Atlas III 18GB drive are shown below. The card easily saturated the capability of the Ultra2 drives tested. The Cheetah drive used the Softraid 2 driver, the Atlas III used the Apple Drive Setup 1.7.2 driver. As seen in the review of the 3 Ultra2 SCSI Cards, the Apple driver provided higher peak rates. Both disks were formatted as HFS+:

Atlas III test results

Comparing the two graphs:


Related Links: (NOTE: Adaptec may change these links over time as products are revised and discontinued. Please email me on any bad links you find here over time.)

  • Adaptec's 3950U2 support page
    (no Mac retail version was ever offered, so their support page has no Mac OS downloads. - previous product page and other links from 1999 have been removed)
    See the above link for 3950U2 Datasheet/Tech specs.

For the latest site reviews on controllers and drives, see the Storage Articles page.

For other Site B&W G3 Articles (HD upgrades, compatibility, speed settings and more) see the links on the main Systems page, Yosemite page and G3-ZONE.


Your Source for the best in CPU/SCSI/VIDEO card reviews, daily news, and more! 

Copyright © 1999.

No part of this site's original content is to be reproduced in any form without permission.
All brand or product names mentioned here are properties of their respective companies.

Disclaimer: Users must read and are bound by the Site Terms & Conditions of Use.