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First post, by pixelatedscraps

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I’m planning to use an Adaptec 2940U2W with the following hardware but as it’s my first time at the SCSI rodeo, I want to make sure I’ve got the correct cables to go with it all.

I believe both of the parts below are 68-pin so would all I need are two of the following cables?

And to maximise SCSI transfer speeds, should I run independent cables for each device or is it okay to run all devices off the one cable in serial?

https://www.ebay.com/itm/Adaptec-Inter ... 632-2357-0

• Plextor PX-20TSi SCSI CD-ROM 12/20x
• 9.1GB Seagate Cheetah 10k ST39103LW

Thanks in advance.

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Reply 1 of 18, by weedeewee

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pretty sure you'll either need a 50p cable or an adapter to convert one of the 68p connectors to a 50pin connector so you can hook up the plextor.

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Reply 2 of 18, by Horun

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Does your 2940U2W have all 3 internal connectors ? 68pin Ultra LVD/SE, 68pin Ultra/FAST and a 50pin SE ???
Yes Plextor PX-20TSi SCSI CD-ROM 12/20x SCSI-2 SE is 50pin. Needs a 50pin cable off the 2940U2W or a 68pin cable to 50pin device adapter.
9.1GB Seagate Cheetah 10k ST39103LW Ultra2 LVD or SE modes, 68pin. Uses 68pin cable like you linked.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor.

Reply 3 of 18, by Warlord

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You don't need a terminator at the end of the scsi cable becasue that CD rom drive has internal termination as long as its jumpered. That means it needs to be plugged into last device on the cable not the very end The end is where the terminator would go. If you don't use a external terminator you have to jumper the drive like I said. But if you ever remove that drive from the cable than you need a external terminator at the end of the cable. So you need this cable here. without the terminator. https://www.ebay.com/itm/332661642133

You can also un jumper the internal termination on the cd drive and put a terminator on the end of the cable but that is unnecessary in your scenario.

This all really assumes that the SCSI card has a 68 pin connector on it just like your drives do and you don't need adapters. I wouldn't recommend using a card that needs an adapter anyways, it will be slower and could have termination issues.

You can ignore the specs of the cable and just trust me that it will be the best cable you can use.

Reply 4 of 18, by weedeewee

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Warlord wrote on 2021-08-15, 18:59:
You don't need a terminator at the end of the scsi cable becasue that CD rom drive has internal termination as long as its jump […]
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You don't need a terminator at the end of the scsi cable becasue that CD rom drive has internal termination as long as its jumpered. That means it needs to be plugged into last device on the cable not the very end The end is where the terminator would go. If you don't use a external terminator you have to jumper the drive like I said. But if you ever remove that drive from the cable than you need a external terminator at the end of the cable. So you need this cable here. without the terminator. https://www.ebay.com/itm/332661642133

You can also un jumper the internal termination on the cd drive and put a terminator on the end of the cable but that is unnecessary in your scenario.

This all really assumes that the SCSI card has a 68 pin connector on it just like your drives do and you don't need adapters. I wouldn't recommend using a card that needs an adapter anyways, it will be slower and could have termination issues.

You can ignore the specs of the cable and just trust me that it will be the best cable you can use.

He will need to get himself a 50 pin cable to hook up the plextor without an adapter, and the termination will have to be set for half of the buswidth on the adaptec, since he'll also be using the hard drive which is a 68pin.
using the cable with integrated terminator, and an adapter to attach the plextor solves this issue without adding to the cable clutter, and termination can be left off on all other devices, just leave it on on the controller.

https://www.ebay.com/itm/222314557974

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Reply 5 of 18, by luckybob

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ho boy. Where do we start.

- Is the CD drive 50 or 68 pin - i'm going to assume 50-pin because 95% of scsi CD drives were 50-pin

Assuming 50 pin CD:

Buy a 68-pin cable that is long enough for your case. Dont spend too much, the controller only runs up to 40mb/s. Spending extra on a U160 or U320 cable is wasting money unless you plan on spending more money. Also, if possible get one with a built in terminator. If you aren't sure if a cable is terminated, look at the end. If you see a relatively large block at one end, that's good. You can buy them seperate. *edit* i see that ebay link to a cable, that looks just fine.

Buy a cheap 68>50 pin adapter. like this: https://www.ebay.com/itm/222314557974 *if your cd drive is 68-pin, you can omit this step.

Set the scsi ID of the HDD to something low. Like 1. (never pick 0 or 7) DISABLE TERMINATION
Set the CD to whatever. The typical value is 3. DISABLE TERMINATION
Assemble the whole mess as follows: Controller > CD > hard drive > terminator. Use the LEFT connector.
It should just work now.

The above should work fine, provided all the parts work. The only caveat is the controller. I don't have it memorized, but the controller should be smart enough to run at 40mb/s when talking to the hard drive, and 20mb/s for the CD. Run some benchmarks on the hard drive. If you see a flat-line limit at 20mb/s then the controller isn't playing nice.

If that is the case, and you want to spend the cash, then you will need a 50-pin cable. All you would need to do is pull the CD off the 68-pin cable and run a 2nd 50-pin cable. the same rules apply as before. controller > drive > terminator. If your cable doesnt have termination (most 50's dont) then you can just ENABLE termination on the drive.

ALL drives with termination enabled MUST be at the VERY end of the cable.

Warlord wrote on 2021-08-15, 18:59:

You don't need a terminator at the end of the scsi cable because that CD rom drive has internal termination as long as its jumpered.

That is a trap for noobs. The cd drive can't be used as a terminator if you are using an adapter. a 50-pin drive can only terminate the 50 pins it has, not the extra 18. So the whole thing won't work. This only applies to 50/68 pin adapters. The terminated drive must terminate all pins and be at the very end of the cable.

It is a mistake to think you can solve any major problems just with potatoes.

Reply 6 of 18, by Warlord

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Theirs 50pin to 68 pin adapters for such things like this one. https://www.ebay.com/itm/222314557974

But he said that he believed both were 68 pin already so unless what he is saying isn't accurate he shouldn't need it.

@ lucky bob not my fault if he didn't give us accurate information.

But yea good advice very idiot proof.

Reply 7 of 18, by piatd

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pixelatedscraps wrote on 2021-08-15, 15:09:

I believe both of the parts below are 68-pin ...

As stated, the optical drive is 50-pin.

And to maximise SCSI transfer speeds, should I run independent cables for each device or is it okay to run all devices off the one cable in serial?

Attaching the 50-pin optical drive to a 68-pin cable will force your Ultra2 HDD (80 MBytes/sec) to run at Ultra levels (40 MBytes/sec) . Attaching a 50-pin device to a 68-pin cable also requires an adapter that blocks--but does not terminate--the high byte. There are additional requirements on this page for exactly where and how such an adapter can be used on the chain.

Instead, run your hardware in the configuration shown in Figure 10. The HDD will use its own 68-pin cable, and the optical drive will use its own 50-pin cable, each connected to the corresponding ports on the adapter card. Note that your HDD does not appear to have a built-in terminator, so you will need a 68-pin cable that has a built-in terminator. The optical drive has a built-in terminator, so you won't need termination on the 50-pin cable itself.

Above all, I recommend reading a good SCSI primer first, or you are in for a world of pain. Unfortunately, the one I use is from a turn-of-the-century A++ certification book, so I'll leave a recommendation to others.

Reply 8 of 18, by Disruptor

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pixelatedscraps wrote on 2021-08-15, 15:09:

Adaptec 2940U2W
Plextor PX-20TSi SCSI CD-ROM 12/20x
9.1GB Seagate Cheetah 10k ST39103LW

Adaptec has a 68 pin LVD connector, an internal 68 pin SE connector and an internal 50 pin SE connector.
Plextor has a 50 pin SE connector.
Seagate has a 68 pin LVD connector.

You need a 50 pin flat ribbon cable to connect the 2940U2W with the Plextor CD-ROM. Be sure that you have the termination on the CD-ROM enabled. I recommend to use a SCSI ID different from 0 and 7.
You need a 68 pin twisted pair cable to connect the 2940U2W with the Seagate ST39103LW. One end of the cable goes into the Adaptec. Use the LVD port, this is the one on the bracket/rear side. The other end of the cable goes into an LVD terminator. The Seagate is somewhere in the middle. The seagate is not terminated. I recommend to use SCSI ID 0.

However, the Adaptec 2940U2W is a cool controller because it has an AIC-3860Q SCSI bridge.
Extending a SCSI bus with Adaptec AIC-3860Q (2940U2W and more)

Reply 9 of 18, by luckybob

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Well, I did a cursory search for "px-20TSi" on the Gargler and I say some images with 68-pins. So I didn't want to just outright assume it was a 50. Granted, I didn't sit there and do a thesis on it, just a 1-minute Gargler image search. I also recall typing

95% of scsi CD drives were 50-pin

The spec sheet for the drive is still available online:
http://www.codemicro.com/support/disc/manuals … i/83329400f.pdf

The spec sheet goes so far as to tell you the drive can produce speeds ~30mb/s average ~37 max. (page 9, if you are so inclined) So even if the SCSI CD limits the bus to 20mb/s (the controller SHOULD be smart enough to adapt) You aren't going to notice much of a difference unless you are literally sitting there with a precision stopwatch on loading screens.

the 1-cable solution should be 1/2 as may potential problems. And if your OCD compels you, like mine does, you can easily add the 2nd 50-pin cable.

It is a mistake to think you can solve any major problems just with potatoes.

Reply 10 of 18, by Disruptor

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Yes, I have an UltraPlex that has a 68 pin connector. Other of my UltraPlex also have wide SCSI, but just on the internal PCB.
But most SCSI CD drives have a 50 pin connector.

Reply 11 of 18, by Horun

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Disruptor wrote on 2021-08-15, 22:22:

Yes, I have an UltraPlex that has a 68 pin connector. Other of my UltraPlex also have wide SCSI, but just on the internal PCB.
But most SCSI CD drives have a 50 pin connector.

All of my Plextors 6x, 12x, and 20x on the shelf and a 32X in a machine somewhere are all 50pin. I have two UltraPlex-40 one with 50pin the other is 68pin wide. I do not think any non "UltraPlex" Plextors had 68pin but could be wrong....

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor.

Reply 12 of 18, by Errius

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I have one of these drives, and yes, it was produced in both 50-pin and 68-pin variants.

[SOLVED] CD Audio cable question

ETA: I have added pictures of both models in this thread.

Last edited by Errius on 2021-08-16, 00:19. Edited 2 times in total.

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Reply 13 of 18, by luckybob

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I have an entire shelf of scsi cd drives, I also can attest to 95% of them being 50-pin. That's not the point. The point is, 1x 68-pin cable should be fine. The only benefit to running both a 50 & 68, is the controller doesn't automatically change bus speed to accommodate the hard drive, and the OP really wants that extra ~10mb/s. If the OP hooks it all up, and it all works, I'll consider that a win. This is their first scsi setup after all. I wanted to keep things simple.

Personally, if the machine has PCI, I will default to SATA. But thats an argument for another thread.

It is a mistake to think you can solve any major problems just with potatoes.

Reply 14 of 18, by Horun

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luckybob wrote on 2021-08-15, 22:51:

I have an entire shelf of scsi cd drives, I also can attest to 95% of them being 50-pin. That's not the point. The point is, 1x 68-pin cable should be fine. The only benefit to running both a 50 & 68, is the controller doesn't automatically change bus speed to accommodate the hard drive, and the OP really wants that extra ~10mb/s. If the OP hooks it all up, and it all works, I'll consider that a win. This is their first scsi setup after all. I wanted to keep things simple.

Personally, if the machine has PCI, I will default to SATA. But thats an argument for another thread.

Your SCSI advise is solid ! Yes should use two cables.

Errius wrote on 2021-08-15, 22:45:

I have one of these drives, and yes, it was produced in both 50-pin and 68-pin variants.
[SOLVED] CD Audio cable question

Odd because the manual for the Plextor PX-20TSi manual shows only a 50 pin back panel.
https://www.manualslib.com/manual/311233/Plex … ?page=18#manual and
https://manualzz.com/doc/2114844/plextor-ultr … ernal-40x-cd#p7 states the UltraPlex Wide (Model PX-40TSUWi Internal and PX-40TSUWe External) is the only Wide CDROM released to date thru 2000.
and your picture is identical to it's back panel in your previous post according to the manual. Wayback shows only the UltraPlex Wide as a 40x
http://web.archive.org/web/19990427192038/htt … com/product.htm
Also shows the 12/20 Plex as the PX-20TSi. So maybe yours had the wrong label or flashed with wrong firmware ??
If Plextor put out a Wide 20x it would be on their website somewhere but I did not find it nor did Google, every search ended with the PX-40TSUW but what does that prove ;p

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor.

Reply 16 of 18, by Warlord

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Thought occurred to me that OP CD drive just has a 68pin adapter already stuck in it so, to someone who isn't paying attention to detail just glosses over it and it looks like a 68 pin. Further inspection might reveal that. Then ya follow bobs advice then.

Reply 17 of 18, by pixelatedscraps

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I’m thinking I’d lean towards having two separate cables. And boy am I glad I asked this question because coming from someone who only knows IDE and SATA, this is nothing simple.

Thanks for all the input, everyone. Some reading to be done…

My ultimate dual 440LX / Voodoo2 SLI build

Test bench: Asus P3B-F | 1.3Ghz Tualeron w/ Powerleap | Geforce 2 Ti500 | SB Live! 5.1 CT4760