SCSI drive adapters

[dudejediknight]

I snatched up a set of 3 SCSI drives off eBay at the last minute since the price was really good. I did a search based on the information in their listing, which seemed to indicate that they would be 50pin like I needed. They arrived today, and, to my dismay, it turns out they are actually 80pin! If I had known that, I wouldn't have bought them, since I don't have anything that uses 80pin SCSI drives. But, since I now own three 80pin drives, it leads me to the real question for the group.

I know that there are adapters to convert SCSI drives, but I've heard that certain adapters are too thick, and thus make the drive unable to fit. The machines I have that need drives (and are the reason I sprung for the drives in the first place) are a Macintosh IIsi, a Power Macintosh 7200/90, and a Performa 6115CD. Anyone have any suggestions for 80 to 50 pin SCSI adapters that will fit within those particular Macs?

 

[equill]

You will need 50/80-pin actively terminated adapters with an included 4-pin power supply input to connect SCA drives into your SCSI-1 and SCSI-2 buses. One example of a source is mcpricebreakers on eBay. High byte (unused) termination is essential to use these LVD drives in your systems, and even then only SCSI Manager 4.3 will make much of a fist of it. You will have to use the drives as single-ended, and their rotational speeds even then will be (probably) more than the native buses in your Macs can profit from completely. However, you may very well get much-increased storage capacity if your OSes are HFS+ savvy. The 7200 should have room behind for the adapter, but count on needing about an extra inch for each drive. 10k or 15k rpm drives may also bring heat dissipation problems.

Don't let price cozen you into buying inadequate/substandard adapters. Your hair has more long-term value to you than a small present economy. Adapters come in 80/50 and 80/68-50-pin forms.

de

 

[dudejediknight]

They are WD Enterprise 4360 drives, but the model number on them doesn't match what's shown on the WD website. Since I know for a fact that they are 80-pin drives, the only 80 pin model they list is the WDE4360-0008, which is a 7200rpm drive. Two of the drives bear Compaq stickers, so the 6008 model probably denotes drives that were originally used in Compaqs.

Right now I'm leaning towards buying a combo 80 to 68&50pin adapter, since it keeps my options open in case the drives don't quite fit into my target Macs.

Also, I remember reading somewhere that high-byte termination was only needed if the drive was larger than 4.5gb. Since my drives are smaller than that (at 4.3gb), do I still need to have high-byte termination?

 

[equill]

You will get most of your answers from a document such as this one, or by Googling. Using only one byte of two has little to do with drive size, and much to do with not getting bitten by the unused upper byte.

'Enterprise' often equates with 'bespoke' or 'made-to-order', which manufacturers often don't list with their standard offerings. There may be difficulties with such drives in ordinary systems, eg when the drives have been configured for Unix environments. Only use will reveal this state of affairs to you, but you can sometimes recover from it with drive utilities other than Apple's.

de

 

[Franklinstein]

Enterprise was the name of the hard drive (like Caviar, Protegé, Scorpio, etc), used only for WD's short-lived SCSI devices. The majority of the Enterprise drives were 7200 RPM, though some 5400 or 10k RPM models may exist. They were quite expensive with relatively lack-lustre performance and consequently didn't sell all that well, so WD killed off that endeavor when they started losing excessive amounts of money in the late 90s. I don't think anybody cried about it.

I once found a 50-pin Enterprise and tried using it in a Mac. It never worked. I could never figure out why. Maybe it just didn't like the Mac's SCSI setup or something, because it would work in peecees. I dunno. It was only a 2GB or something, so I really didn't bother to pursue the issue.

 

[Anonymous Freak]

Once upon a time, I got an 18 GB 1/3 height (i.e. about 50% again thicker than your standard 3.5" hard drive; the same height as a standard desktop CD-ROM drdive,) 10,000 RPM SCA (80-pin,) hard drive dirt cheap. (It was still a 'current' drive at the time, and I got it for about 25% retail value because the guy hadn't a clue what he had bought it for, not even having a SCSI card, and just wanted to be rid of it.)

I found a rather low-end generic SCA->68/50 pin adapter, and slapped it in my workstation. Worked great. Noisy beast, generated more heat than my main CPU, but it worked great.

After that workstation got retired, I even put it in my SE/30 for a while. Worked fine. (Didn't run it for long periods of time for fear of burning out the little SE/30's power supply. Ended up powering it externally, and adding another fan to the SE/30 to run it.

 

[Unknown_K]

I have a bunch of SCA drives in use, the key is to have a good cable and proper termination.

Current'y I have a 4GB SCA drive with that 50/68pin adapter and little terminator in one of my IIfx units, works fine on a jackhammer (using 50 pin since I am short on 68 pin cables and the drive won't do more then 10MB/sec anyway).

 

[dudejediknight]

You will get most of your answers from a document such as this one, or by Googling.

I already found that document, or one just like it, and it didn't really give me any more of an understanding than I had before. SCSI was never my strong suit, as it seems inherently confusing. Plus this whole adapter business is adding an extra layer that I wanted to avoid by buying 50pin drives to begin with.

The bulk of my SCSI knowledge relates to the external end, adding Zip drives and such. I've never dealt with internal SCSI before... and since these machines don't have their original drives, I have nothing to compare it to. I know that the Mac end of the chain is automatically terminated, but... how is the other end terminated? Was that something the original hard drive did? If so, then whatever drive I put in to replace it would have to do the same. Since 80pin drives don't do that on their own, the adapter would then need to terminate the chain (short of attaching a separate device just to terminate the chain).

As for high-byte termination, this makes it seem like it has to do with using any 80pin drive on a 50pin chain. All the adapters I've seen don't say anything about terminating or not terminating the high-byte, and I think that's whats getting me so confused. Do all the adapters have high-byte termination automatically, or is it a feature I have to specifically ask for?

That's my understanding of the situation... hopefully it's accurate enough to make this all work. Otherwise... I'll need somebody to spell it out for me in nice, simple terms that any idiot would understand. [] ]'>

 

[dudejediknight]

I hate to drag this back up, but I haven't quite figured this thing out yet. Plus, the lack of any sort of response makes me worry that I'm somehow missing something obvious.

A lot of research has gotten me closer (at least I think it's closer) to the answer I need, but I'm still not clear on exactly which adapter I need to buy. I've already decided that I want to get a combo 80 to 68/50 adapter (if they don't/won't work in my old Macs, plan B is to use them with the 68pin SCSI card in my blue&white, probably as a RAID).

I've already spelled out my situation and gotten a basic picture... but finding an adapter that matches that picture is not going so well.

• First, the SCSI chain needs to be terminated, which means the replacment drive needs to be terminated. Since 80pin drives don't do that on their own, I need the adapter to terminate the SCSI bus. Problem is, none of the adapters I've seen listed state whether they do or don't do that. If they don't say either way, does that mean it does or doesn't terminate the chain?

To be able to use the same adapter for both cases would mean that I need to be able to select whether the adapter terminates the chain or not. Is this correct? If so, that means that trying to find one adapter that would work in both situations means that it needs to include the option of setting whether it terminates the chain or not. Otherwise, I have to focus on finding an adapter to fit my plan A, and should that fail, move on to finding a different adapter to fit my plan B. Makes sense, right?

• Second is the deal with high-byte termination. Since I'm only using a single drive in each machine, and no drive is larger than the 4.5gb boundary I've read about, then I shouldn't need to have an adapter with high-byte termination. Which is fine by me, since including it seems to drastically increase the price.

High-byte termination is one of those features you have to specifically ask for, so if it doesn't say so, then it's not included. Correct?

• The last issue is an issue of size... if the adapter is too large, then the drive/adapter combination won't fit into the machine. I assume smaller is better, but short of buying one and trying it myself, I don't really see another way of knowing for certain.

Because of this, I don't see a reason to buy 3 adapters at once, just to find out they won't fit in my target Macs. I believe I should just buy one and see if it fits in each of the 3 machines. Then, should it not fit properly in any of those situations, I will have better knowledge of the size I will need for that specific situation. Simple common sense, right?

I would really appreciate it if somebody could reassure me that my reasoning is accurate. That would make me a lot more confident that I won't be wasting any more time and energy barking up the wrong tree, so to speak.

 

[trag]

I think you've mostly got it right, but I would not assume that adapters lack termination simply because it is not mentioned. Mind you, I wouldn't buy one from a seller unless it is mentioned.

The thing to understand about shopping for SCSI stuff is that most of the sellers don't seem to understand or think about what they are selling. The number of sellers of SCSI drives on Ebay who don't bother to mention whether a drive has 50 pin, 68 pin or 80 pin connectors is just astounding--as you discovered to your dismay. Plus there's a joker selling SCSI hard drives in the Mac Ebay sections advertising them as 50 pin drives when they are really 80 pin drives with adapters attached. The clue is that if you read his whole item description, you'll notice that he says he can sell the same drive with a 68 pin adapter instead of 50 pin. Oh, and as much as I detest that seller's practices, I think he sells the adapters too, so you might hunt him down and check.

Anyway, so shopping for this stuff is a pain, and there's not much any of us can do to help you. You must either email the sellers with your specific questions and hope that they respond in a meaningful, honest and accurate manner, or find a local store where you can buy them. if you have a Frys or an Altex Electronics locally, I'd recommend that you try there.

As far as understanding termination goes, it is fairly simple in the broad outlines but gets complex in the details. At it's simplest, the rule about SCSI chains is that both ends must be terminated and nothing else must be terminated.

Termination is a configuration of resistors (and IIRC capacitors) on the wires of the cable, but in practice there are four possible sources of termination. There is internal termination in SCSI devices such as hard drives. This is turned on by installing a jumper or off by removing the jumper. There is termination built into the SCSI controller circuitry on later Mac motherboards. The PCI Macs definitely have it. There is SCSI termination built into various SCSI cards such as PCI and NuBus cards. And there are external SCSI termination blocks which you attach to the SCSI cable or plug into a spare SCSI connector on an external SCSI box. Oh, and I suppose a fifth would be termination built into adapters such as you are looking for.

The system of cabling connected to a single SCSI host or controller must form a linear chain. In this case the SCSI host is your macintosh motherboard, but it could be a PCI card if you had a SCSI card. The host need not be at the end of the chain; it could be in the middle if it has connectors for two SCSI cables. In your case, you're only talking about internal devices, so the host will be at one end.

If you are only using internal SCSI devices, then this is pretty simple. Your SCSI chain will look something like this:

T:MB=======HD=========HD=========HD:T

Where MB is motherboard, HD is hard drive, ======== is SCSI cable and :T is a terminator associated with the neighboring device. So in the case above, the left hand termination is on the motheboard and the right hand is on the last hard drive on the cable.

Now 50 pin vs. 68 pin, narrow vs. wide makes things more complicated. Let's use ------ for narrow cable and ==== for wide cable.

What you really have is:

T:MB----------------=HD=------------=HD=-----------=HD:T

Where the little bit of = around the hard drives is there to represent the fact that 80 pin SCA drives are really wide devices.

Now here's the complicating factor. There is termination for the narrow portion of the SCSI cable, but there is also a small block of termination associated with the wide portion of the SCSI cable. So, in the diagram above, the wide portion of the middle two hard drives has no termination. The wide portion is also not used, so you wouldn't think it was an issue, but it is.

So here is what you need:

T:MB--------------=HD1:HBT=---------=HD2:HBT=----------=HD3:T

Where HBT is High Byte Termination. High Byte Termination is termination of only the high byte of the cabling. You do not want to terminate the lower 50 wires, because then you would have termination in the middle of the SCSI chain and that is bad. Termination should exist only at the two ends, except in this special case, where the wide nubs are connected to nothing and so form their own little isolated high byte SCSI chain which needs termination.

So, you need a terminator on the adapter on HD3 which will terminate all 68 pins of the cabling. High and low byte termination. That's just normal 68 pin termination. But you need adapters on HD1 and HD2 which are capable of just terminating the high byte without terminating the low byte.

The motherboard end configures itself automagically, so you don't have to worry about that for this configuration.

Alternatively, you can do this kind of thing:

T:MB-----=HD1:HBT======HD2=======HD3:T

Where you have wide cable between all the hard drives, so you just terminate the high byte at the two ends at HD1 and HD3. Of course at HD3 you also have to terminate the lower 50 pins because they end there too.

The problem with that last configuration is that there really isn't any cabling in the world that will let you do it internally. That is a more practicle arrangement for external SCSI chains, where you have separate cables between each device (instead of one continuous cable with many connectors) and you can just switch from narrow to wide on the back of one of the devices.

Jeff Walther