Re: NOT a lot different
- From: Arie Bant <abant@xxxxxxxx>
- Date: Mon, 04 Jul 2005 02:20:01 +0100
On 03/07/05 02:52, George Hester wrote:
Whatever all that means I can see you put some thought into it. I will keep that for reference thanks.
My pleasure George.
My advice to you is, if you want to work with SCSI, you should try and learn so much about it that at least you know what it is about at a conceptual level and where you can find specific info if you need it.
Search Google for "SCSI Glossary".
For now, what did you not understand that makes you say "Whatever all that means"?
Arie Bant.
-- George Hester _______________________________ "Arie Bant" <abant@xxxxxxxx> wrote in message news:da2ahd$vug$1@xxxxxxxxxxxxxxxxxxxxxxxx
On 30/06/05 23:40, George Hester wrote:
"Arie Bant" <abant@xxxxxxxx> wrote in message news:d9vfbj$3bk$1@xxxxxxxxxxxxxxxxxxxxxxxx
On 29/06/05 04:34, George Hester wrote:
Well thank you that was my intent all along. The ones you see at my
second
post are the ones I have. So I think you can understand why when I saw
what
I saw at eBay I was wondering why they didn't look like mine.
They look like that because passive termination has become obsolete and no manufacturer I know of puts passive termination on anything these days, because "narrow" 50-pin cabling is not compliant with LVD and because the internal LED is generally rather useless compared to having a LED on the front panel of the machine and it saves money not to put it
on.
Quite honestly I can only explain your "wondering" as a result of a lack of understanding of SCSI. With respect, there is no rational explanation why one should expect new SCA adapters to look like those used before "ULTRA" SCSI was introduced.
-- George Hester _______________________________ "Arie Bant" <abant@xxxxxxxx> wrote in message news:d9sua3$9dt$1@xxxxxxxxxxxxxxxxxxxxxxxx
On 21/06/05 23:24, George Hester wrote:
Yes but will the ones I see at eBay work? That's my issue. They
don't
have
LEDs what else don't they have? The ability to work?
Depends on what you mean by "Work". Just having had a second glance I noticed that some of the things you described as connectors are not, they are Jumpers. The adapters your URL pointed at are infact not so standard, but very expensive. There are two differences with the cheaper ones you pointed at in your first posting:
1 These have built-in SCSI terminators, rather unusual and the large number of jumpers looks to be there to enable/disable the terminators. 2 These are not LVD compatible, i.e only useful with old kit.
Did I say they are expensive? Shamefully so!
It seems your understanding of SCSI could do with reading some basic information on how it works.
-- George Hester _______________________________ "Ron Reaugh" <ron-reaugh@xxxxxxxxxxxxxxxx> wrote in message news:yXmte.338823$cg1.129226@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
"George Hester" <hesterloli@xxxxxxxxxxx> wrote in message news:Msgte.26217$fp6.5436@xxxxxxxxxxxxxxxxxxxxxxx Here this is very similar:
http://www.corpsys.com/store/prodinfo.asp?number=SCA2SCSIT&variation=&aitem=
25&mitem=34
That's the standard product. One with all those extra
headers/connectors
is
not anything usual.
With all due respect, "there is no rational explanation why one should expect new SCA adapters to look like those used before "ULTRA" SCSI was introduced," because that is what I have and they work. That seems
rational
to me not to you?
-- George Hester _______________________________
Dear George,
I'll try again to explain in more detail.
The SCA adapter you have "looks" like it does because it has passive terminators (the three yellow resistor SIL-packs) on board and some jumpers to enable or disable these terminators and because it has a "narrow" or 8-bit 50-pin connector. All that was fine in the days of 5 and 10 MHz SCSI bus speed and SCA-1. Since ULTRA SCSI and above (Ultra2, Ultra3/160, Ultra320) the SCSI bus can operate at speeds in excess of 20 MHz (40, 80, 160 Mhz). At these speeds and for some other technical reasons, passive termination does not work reliably if at all and in the case of a LVD bus it simply does not work. So it has become obsolete and I know of no manufacturer that still incorporates passive termination on SCSI interfaces.
You state that you have Ultra SCSI working with these adapters. That is very well possible. What you do not explain is what termination you use. You could use an separate end-of-cable terminator of the active sort or you could even use the build-in termination of some other non-SCA SCSI device, active or not. Perhaps you do not use active termination at all but passive termination. Perhaps even the terminators on the SCA adapter. All that is possible and may work, albeit that in the case of passive termination the bus probably runs at a lower speed, i.e. 10 Mhz (=20 MB/sec), not at 20 MHz (=40 MB/sec). Unless you do some measuring you would not neccesarily know the true bus speed. But in the right circumstances, only one device on the bus, a short internal cable, you could be lucky and get away with it. A matter of chance.
That is not what SCSI cabling now is designed for. In particular the $9 SCA adapters are explicitly advertised to be ULTRA320 compliant. That means that passive termination is definitely useless because ULTRA320 uses Low Voltage Differential signals on the bus and that just does not work with passive termination. For the same reason there is no 50-pin connector on that adapter, ULTRA320 is almost exclusively used on hard disk drives with a "Wide" (=16 bit) interface and that excludes the 50-pin connectors. You may also note that this adapter is lower than your older ones. That is because it is made to fit behind a low profile 3.5" device, aproximately 25 mm high. The older ones were made to fit behind a "half height" drive, approximately 40 mm high, so they had some more space for extra
components.
I hope it is now clear to you why you cannot expect this SCA adapter to look like your other ones.
Regards,
Arie Bant.
.
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