2940 Taxonomy; was: Re: SCSI cable needed

Roger Merchberger zmerch-cctalk at 30below.com
Wed Sep 27 15:59:34 CDT 2006

Rumor has it that jim stephens may have mentioned these words:
>Jeff Walther wrote:
>>>Date: Tue, 26 Sep 2006 19:19:55 -0400
>>>From: "Roy J. Tellason" <rtellason at verizon.net>
>good summary Jeff.  I cant see anything you got wrong, but might
>clarify that there are two terms in the naming of these boards and
>others that need to be mentioned.
>the W stands for Wide, or 16 bit, or 68 pin connectors.  It is true
>that you can have W with SCA type 80 pin connectors as well.
>the U stands for Ultra Scsi which is the 40 mb/sec or greater.

Erm, not quite. Ultra *can* be 20MByte/sec - if it's a narrow (8-bit) buss. 
I've had a few Ultra drives that were only 50-pin.

>Scsi orignally was 5mb/sec.  then it was doubled by doing
>what was originally called synchronous mode to 10mb / sec.

=-= A couple of skipped steps in the history... =-=

Then, IIRC, Ultra and wide came out at about the same time, each supplying 
20MByte/Sec - Ultra by increasing the bandwidth, Wide by increasing the 

Then someone got smart, and stuck 'em together for Ultra Wide, and that 
gave us 40Meg/Sec.

>then ultra 2 came out and went to 80 m / sec.   I found a
>page that was out in 1988 announcing the Adaptec products
>coming which was the AHA-2940U2W which had the
>dual channel chips and U2 transfer rate.  That is probably
>the double 68 pin internal board you are speaking of.
>It claimed that the U2W board also supported LVD
>The latest transfer rate is Ultra 160.  I don't have any
>info on those drives.

Ah, no. The latest transfer rate is Ultra 320 - it's been out for at least 
a few years now.

>I think the 80 pin SCA is only a matter of the hot plug
>spec and connector, and can be dealt with by adapters
>from the 50 pin or 68 pin cables to the SCA back
>plane connectors.  It also deals with the device address
>in the connector.

Although there are 50-pin to 80-pin adapters, remember that 50-pin is only 
an 8-bit-wide bus and so your throughput would not be any faster than with 
an 8-bit-wide device (of the same bandwidth).

Hope this helps,
Roger "Merch" Merchberger

Roger "Merch" Merchberger   | A new truth in advertising slogan
SysAdmin, Iceberg Computers | for MicroSoft: "We're not the oxy...
zmerch at 30below.com          |                         ...in oxymoron!"

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