This post could also be in the PPC Forums, or Other Technology, maybe even Hardware Hacks. Admin, please move if necessary. This should have been done a long time ago (and it should be repeated for ATA/IDE interfaces). There are so many different drive interfaces, and most descriptions are incomplete, and/or confusing. What I'm posting is merely a starting point. Hopefully others will post their knowledge, and eventually enough info could be put together to request an entirely comprensive scsi reference info page for Macs here at Applefritter. The main problem I see is that "scsi" is a catch all term for any scsi interface, usually meaning a particular interface, but possibly meaning something different than the usual. What I'd like to see is all Mac models listed with the type of interface including the number of pins for the interface, its actual scsi designation and the multiple names meaning the same thing, a treatment of scsi termination (all terminated? or just one of multiple drives terminated?), as well as a treatment of NuBus/PCI cards available (discontinued or otherwise) with their scsi multiple-interface/pin designations outlined. Better... a sort of glossery, starting with the # of pins, scsi designation, other names and references back to them in the glossery, data transfer rate, Mac models that used it, and different NuBus/PCI cards that supported it, software drivers necessary, etc. I realize there will be redundancy, but that would make it easiest to look up anything in particular. This sounds like a big project, but technically there are a finite number of scsi designations, so I don't see any problem including all this information on a single reference page. I've seen other reference pages on the internet, but they are never fully comprehensive.
Here is the quick breakdown (please feel free to correct errors/add info):
- 25-pin SCSI-1: Uses an 8-bit bus, and supports data rates of 4 MB/s
Any models use this internally? Are all the 25-pin external connectors on Macs SCSI-1? - 50-pin SCSI-2, Fast SCSI: Same as SCSI-1, but uses a 50-pin connector instead of a 25-pin connector, and supports multiple devices. This is what most people mean when they refer to plain SCSI.
Isn't this identical to Fast SCSI? Lets make it clear what the multiple scsi names are for the same damn interface!. Aren't there SCSI-1 interfaces that also use 50-pin?
The PowerMac 8600 has both a SCSI-1 & a SCSI-2 bus, both are 50-pin on the logic board, but the SCSI-1 interface has an external 25-pin connector. - 68-pin SCSI-2, Fast SCSI
- 68-pin Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit transfers.
How can you tell the difference between Wide interfaces and Fast Wide? What's the data rate? - Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data rates of 10 MB/s.
SCSI-2? 50-pin? - Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 MB/s.
Are there NuBus cards that support this in 68k Macs? What are they? How many pins? Is this the true interface inside an Apple Network Server? - Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20 MB/s.
Which is superior, Ultra SCSI, or Fast Wide? - 68-pin SCSI-3, Ultra Wide: Uses a 16-bit bus and supports data rates of 40 MB/s. Also called Ultra Wide SCSI.
Are there SCSI-3 50-pin drives, or are they all 68-pin? - Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MB/s.
What is the purpose of the different bus speeds? Why did the technology advancing like this, with both 8-bit and 16-bit bus speeds, yet sometimes identical data transfer rate? - Wide Ultra2 SCSI: Uses a 16-bit bus and supports data rates of 80 MB/s.
What are the cards that support this? - Other:
What effect do adapters have on scsi data transfer rates? For example, the 80-pin IBM SCA type connectors will always need adapters... which are made for 68-pin and 50-pin... what is happening here? ... effectively turning a drive from one scsi to another? Are faster SCSI drives always backwards compatible with earlier scsi interface technologies so long as you have an adapter? For instance, can you put a Ultra2 SCSI SCA drive with an adapter in a machine with 50-pin SCSI-1?
Fast scsi, ultra scsi, etc you can pretty much ignore (marketing terms). The important thing is what version of the scsi spec is used (scsi 1,2,3 or the newer ones which are based on MB/sec throughput - u160,u320) and if it is wide or not.
The 25 pin variant of scsi used as the external apple interface was actually released before the scsi spec was finalised. It is basically the same as 50 pin scsi with all the ground wires tied together. I think it was backported into the scsi spec, but the standards people never really liked it.
The different bus speeds thing probably comes down to parallel vs serial transfers and their suitability for server environments - more bits wide would give you greater throughput I'd imagine (and better resistance to crosstalk). By the time the scsi-2 spec was released I'd imagine wide scsi had also got faster - so you gotta look at it all in context.
Adapters from 68 to 50 either ignore or terminate (best) 8 bits of the cable. I guess the controller knows how to deal with this??? No idea what affect this has on throughput.
There are a load more scsi variants, LVD, HVD, Fibre Channel, etc. Most are only really used in server situations. There is a scsi faq online http://www.scsifaq.org/ & I think that same guy has written a book about it if your really want to get into it.
Also - SCA connectors just combine power and data on the same connector (for easy hot swappability) - the adaptor would basically break this out into seperate connections, so it shouldn't cause too many issues.
This is the sort of post I was hoping wouldn't appear... the ah, its easy... "all the info is here" and the "pretty much ignore these..." kinds of things. (But please don't let this persuade anyone from posting anything they like.)
I took a look at scsifaq, and while comprehensive, I suppose, is in and of itself a complete clusterfsck. Also, it makes no mention of any Apple product as far as I can tell.
The reason why the "marketing terms" cannot be ignored is that people use them. Most here at Applefritter will be buying their scsi drives 2nd, 3rd... and 10th hand off eBay, or pulling them out of other machines. Some online auction sellers rule... simple auction page simply describing what's for sale, the best have references to product specifications. Others are more annoying, and insist on using all this crazy stuff on their auction that, I swear, is meant to confuse and ensnare buyers. I just can't stand it when their "terms," obviously generic and duplicated across all their acutions, end up being 20-100 times longer than their lame ass one line description of the item. And many of them only use the so called marketing terms.
As far as the average Applefritterer is concerned, there is a lot less information s/he actually needs than what's buried in that faq... there are a lot of sites like that, and they just don't do us service as far as finding quickly what we really want to know.
-short explanation of all the scsi interfaces, and other duplicate nomencature, official or not, in some sort of sensical order that includes data rates
-what Macs use what interfaces
-what number of pins in what connectors correspond to which interfaces
-what expansion card options are there
With the number of people here tooling with legacy and classic macintoshes, and the fact that most all of them use scsi, and that most everyone wants to beef them up, its not at all an odd request to have a page dedicated to scsi as it applies to Macs to stand as a quick reference.
Well I did try to answer some of your questions & short of writing a bible in a post I just tried to cover a few points and provide a resource for further research.
Saying "not good enough, I want it all!" isn't going to get you anywhere. I'm not saying I have all the answers, but it's pretty lame to criticize me for trying to help - and you can't expect everything to be served to you on a plate.
Alot of the confusion comes from folks not understanding the need to differentiate between the hardware interfaces and the protocols that pass through them. The number of pins involved in no way dictates the speed of the connection, except that a wide interface generally has double the bus width (and roughly double the data capacity) of a same-protocol narrow interface. An Ultra 80 device could have any of several possible hardware interfaces - eg: 50 pin, 68 pin or 80 pin.
I think the most revealing way to describe the variety of interfaces and potential transfer speeds would be with a 2 dimensional chart, graphed as physical interface spec in one axis and protocol in the other. I googled for an existing chart of that type but no joy. I did however find lots of other interesting and useful infos . . .
here's some links:
http://www.pcguide.com/ref/hdd/if/scsi/index.htm
http://www.storagereview.com/guide2000/ref/hdd/if/scsi/summary.html
http://en.wikipedia.org/wiki/Scsi
http://www.paralan.com/artech1.html
http://scsifaq.paralan.com/
http://www.scsilibrary.com/
http://www.t10.org/scsi-3.htm
That last one is pretty interesting . . .
hth,
dan k
Take a look at this auction
OK... 1.6" high, 3.5" 50-pin scsi drive for $42.88 + @ $12 shipping...
At first glance, this sounds like a decent deal. I love Seagates for their warranties. This one only has a 1 year warranty unlike the usual 5 year Seagate warranty, but I think its because its not new, but 'like new." Its a thick drive, but I think I could fit it in the boxes I might use it for... so at first, I think, I might even buy 3 of these.
But the first indicator of "you're gonna get screwed" is there, and an oh so common one it is... via a lot of flashy annoying crap on the auction page... and the second indicator, the big clue... no picture of the connector...
So... reading down, it says it has a "Ultra2 SCSI-1 50-pin Centronics" connector. WTF??!!
Now, the connector we're all familiar with, what we really want, and when we hear "50-pin," the first thing that comes to mind is
Its the internal, on-board (not PCI/Nubus card) scsi connector of every mac I've ever seen, and it may be scsi-1, scsi-2, and I believe the ANS has it but its actually Fast Wide scsi. Getting a drive with this as the native connection eliminates problems, like having to get an adapter, which in and of itself isn't so bad until a) you find out how fragile they always are and b) you discover that once the adapter is attached and the cables connected, you can't fit it where it needs to go, and the whole thing becomes worthless.
Slightly less well known, when we hear "Centronics," what pops to mind is
But... this is an external connection... does Centronics have an internal connector? Beats me.
And even less well known is Ultra2, but if you know it, the connection that pops in your head is something along the lines of
So here's the delimma, and the good (not the best) example for the need for a sort of scsi Rosetta stone for Mac enthusiasts. Yes, you can write the seller and ask questions, but without pictures, you are just as likely to be as confused as when you started. Now... for all I know, this is exactly what any legacy mac owner would want (well, a 1" drive would be nicer, and with the 5 year warranty would be even nicer)... but without someway to be exactly sure, you really just don't know until you buy it and it arrives, causing all manner of needless stress and a shortened life span.
Yes, its nice to post links to other sites with bountiful information, but it just becomes easy to make mistakes and be lulled into the sense of you've finally figured it out, when really you haven't, as you discover only when your new drive arrives and its like nothing you've ever seen before.
Just how many different scsi connectors, internal & external, are there? Can't be more than 20, right? How many different variations of scsi standards are there? Again, I doubt its more than 20. So I am imagining this relatively simple page with ALL the info a mac user wants regarding scsi, and none of the information that just won't help them. Set it up myself, you say? I would, but as you've probably guessed, I am easily confused by ambiguous nomenclature, and I've really only been exposed to a very few types of scsi and its connectors. There are some incrediblely knowledgeable users here... this is an ask... it is a request, a plea... (I can't be the only one) for the love of God, please help end the madness of Mac scsi suffering! (maybe over the top? Well, like they say... you can never be too over the top)
So did you ask this seller for photos? Anyone with a couple of dozen of these drives to sell, and who can put together such an elaborately designed listing, but then doesn't include photos sounds like a joker to me. I suspect you hit it on the head with the centronics thing. That's probably why he doesn't include pics. He lures you in with the 50pin description, but fails to point out succinctly that he means 50pin centronics mesh (some very odd old design, probably military use or something), but does mention centronics once in a very verbose listing. Then when the unsuspecting buyer complains, he can say it was right there in the listing. Standard eBay drive-seller disreputable BS. There's always a dozen guys on eBay trying to get Mac users to buy old SCA drives by claiming they're 50pin, and only mention once in the listing in small print somewhere that they're SCA with 50 pin adapters.
That's the connector the drive will have. Internal drives don't come with Centronics connectors, since they're meant to work with ribbon cables. The drive in the auction has a standard 50-pin SCSI connection, like the kind you'd find on a Mac motherboard for use with internal drives.
The question is, Dr. Webster, how are you so sure? Just because you think it must be, don't make it necessarily so.
Why would you buy a drive without knowing the model number? The seagate page should tell you the required info (along with showing you pictures of the drive itself) once you obtain this from the seller - I agree the description isn't exactly clear (and I have never heard of a 50 pin centronics connector on a scsi drive).
I'd say there would easily be more than 20 scsi variations (mostly at the server end of things) - SCSI is a huge number of specifications encompassing 20 years of development. There would be probably be under 20 interfaces, but not much under 20 - not many would be relevant to macintosh users though. 68,80 and 50 pin are the only ones of concern (for hard drives).
I'd say the seller is mistaken about it being centronics, and if this is not true then anything else he has said might be bollocks also.
The 80 pin SCA connector is a type of centronics connector ("micro-centronics") - but is certainly not 50 pin.
Based off of the seller's description, I made an educated guess.
I did some more digging, though, and it looks like the seller doesn't quite know what they're taking about. I think this is the drive they have for sale:
http://www.seagate.com/support/disc/scsi/st150176lc.html
I completely agree... where's the photo? But I have to give the seller the benefit of the doubt... maybe they are unaware of what Mac buyers are looking for... maybe its a hardship to post images (it does cost for more than one image per auction), maybe having multiple auctions almost requires the seller to use these standard cruddy techniques to save time.
The real issue is that this is what most of the auctions end up looking like. There is the rare auction where the seller makes it wonderfully clear that the drive is in fact the regular 50-pin internal interface and doesn't require an adapter and will work with all Macs... but it is the exception.
My point is that these type of auctions are pretty normal, pretty regular... so its what we have to work with, what we have to adapt to (can't change the world, just yourself)... I want the tools to be able to quickly decifer it all before I actually have to contact the seller.
Furthermore, and frankly, I can't stand eBay's messaging interface... it could be so simple, but you end up getting this bloody mess of a response, an email filled with total junk surrounding the one or two line response, and no copy of the original question asked. I get responses back from sellers and I have no reference to what the heck its about... I have to go look up the auction by the number, then try to remember what I asked, or look around for the email I sent to myself that included the question. I'm sick of that. The interface makes me just never want to use it... unless I absolutely have to. The easy solution is to request corresponding by email with the seller, but its just an extra step... it shouldn't be necessary.
At any rate... back to our story... lets say the kind of page I'm requesting has 50 scsi protocols/interfaces, whatever. Its still finite. How much scsi development is still going on? Once the page is up and complete, I expect it would remain pretty static. Is what I'm asking for here just too big of a request? That it would take more time to complete than the amount of time it would cumulatively save helping mac enthusiasts?
Based on this auction, I think the seller just assumed that since the external connector was called Centronics, the internal was too.
Read up some more on the subject, all will become clear!
A quick visit over to Seagate (as Doc W and I just did) revealed the auction you mention includes a ST150176LC (it's the only 50.1 GB Barracuda), which has an 80 pin SCA (Single Connector Attachment) connector. Obviously, if the vendor is selling it as a 50 pin drive, it must also include an 80 -> 50 adapter. SCA connections include signal, power, termination options and ID selection all in one connector.
The 50 pin connector on the adapter is certainly going to be an IDC 50 pin male, suitable for connecting to a standard internal 50 IDC ribbon cable. See your photo above labeled 50-pin SCSI.
Frankly, I'd not worry too much about the details. The vendor asserts they've tested the drive on a Mac's internal 50-pin SCSI bus. If the vendor's cred is good and the price is right, either buy the drive or move on. Is a photo necessary?
Really, I'll repeat myself here. You're confused because you continue to misunderstand the difference between physical connectors and the protocols carried by them. Please go up the page and read through those links I provided. Once you've grokked all of that, you will no longer be confused. Well, about SCSI anyhow.
Plus, once you've acquired this knowledge, you can write the page-for-which-you-yearn yourself!
dan k
PS: here's some more links culled from this google search . . .
http://www.interfacebus.com/Design_Connector_SCSI.html
http://pinouts.ru/pin_HD.shtml
http://www.mycableshop.com/scsicableguide.htm
http://www.mycableshop.com/techarticles/scsiprimer.htm
http://www.mycableshop.com/techarticles/scsiconnectors.htm
http://www.connectworld.net/cables/scsifaq.html
Also, Scott Mueller gives a clear explanation of the various types and history of IDE/ATA and SCSI in the long-reffered "Upgrading and Repairing PCs" which anyone familiar with repairing PCs should have heard of or seen. It's a PC based book, but he covers enough tech in such detail that even Mac users will benefit from it. Just his clear explanation of SCSI is worth finding the book at the library. I'll just about guarantee they'll have a copy of one of the 16 editions...
Then, when somebody has an explanation similar to that, then we can go in and make the Mac to SCSI list/table as described in the OP and by DanK.
Why worry about the details? Well it's horribly misleading for one and probably deliberately deceptive. I doubt a seller with 400 feedback would not have a digicam.
The seller did say 50 pin centronics also - so add just plain wrong to the list.
I'd stay well away.
This topic might be of some assistance also:
http://www.applefritter.com/node/9176
I just put an SCA drive with a 68pin adapter in the top bay of a Beige G3 desktop for a friend. Luckily I had a cable that made it possible. The first 68 SCSI cable I tried would not have worked because there wasn't room with the adapter. Adapters can definitely have fit problems on some machines, so plan ahead.
I've done my best to expain the need for a simple scsi explanation page... but most can't see the point.
Yes... we can ask the seller for a picture of the connecter, and to specify the drive by model number. But that takes time. I don't know who goes to an auction site and picks out a single auction and eliminates that auction before moving on to another. I search for what I need, and investigate multiple auctions simultaneously. If I'm looking for a HD, for instance, I may have a dozen candidates. And guess what... most all of them are looking the way my example looked. I'd love to eliminate all those kinds of auctions... but that would be clearing 80-90% of the possibilities. So I have to send out a dozen messages, then wait for a dozen answers, match up the answers with the auctions... its a pain... takes way too long.
Yes, I can go to Seagate, search for 50gb drives, download the pdf manual, search through it... figure out what kind of connector .... but this would all be much easier, faster, simpler if there were a scsi info page dedicated to mac... It doesn't have to be all that complex as the sites that have been thus offered. We don't need the world history of scsi, or any sort of self-promoting marketing.
I don't want to read some scsi site that has too much information, and makes no mention of macs whatsoever... or sift through multiple links of the same confusing stuff.
Most of you seem to be either of the philosophy give a man a fish, or teach him how to genetically engineer his own.
I don't know why I can see this so clearly, and no one seems to notice that it might be useful to us.:
cross-referenced with
and some short summary of scsi, termination, anything else that might be useful like which adapters are available
ALL this on one or two pages... no lists of links separating everything into its own category, no links to pages of more links for more information... just the nitty gritty, just for macs
cat, you are trolling.
You have ideas about what would be the best way to do what you suggest - how about going ahead & making a start?
If, in the process of writing such a FAQ, you are confused on specific points, feel free to ask a specific question and I'm sure people will try and help.
BTW: What you ask for would NOT fix the problem of a misleading ebay listing such as the one provided. You would still need to ask for clarification from the seller and look up the model number.
Well, maybe you should get it started. Go get the images of the 20 or so types and post them here and let anyone who knows post the stats for each.
The simple rule with all auctions is, NEVER ASSUME (you know what they say about assume). If you can't get it from the horse's mouth then all you're doing is rolling the dice.
The first photo on an eBay auction is free. No big deal. You'd think anyone who went to so much trouble to get all the stats and list them would have the time to take a pic. And how'd he come up with "50 pin centronics?" That's pretty bad if it's someone who knows what all the other stats on a harddrive mean. He would have had to have made that up himself. Why did he use that and not the interface type that would have been listed with all the other stats he found? And even if you had all the info you're looking for, it wouldn't have helped you at all with this auction.
Has anyone messaged the seller yet and told him we're talking about him?
That's what this is... see the top post... I made a good start there. No one wants to add to it... but would rather point somewhere else. Sorry if stating the obvious is a troll.
Well, it might help a little. Obviously the seller's description of the interface makes no sense (Ultra2 SCSI-1 Centronics huh???!!), but they tend to get the data transfer rates right (even though I don't think this one is right either... not 5MB/s, not 10MB/s, not 20MB/s, but 22.5 MB/s!!) as they believe that it is a big selling point not realizing that if they are trying to sell it on its 50-pin merits that the increased data transfer rate means little, as it is bound by the scsi bus of whatever machine an intended buyer would put it into, usually fast scsi, 10MB/s. So... knowing a data transfer rate is a small clue... not the definitive answer, but a clue in that it will eliminate many other possibilities. (Its nice that scsi is backwards compatable, I guess.)
transfer rates being correct or close... it would help a little in eliminating many possibilities
I just did... curiousity got the best of me... asked for a picture
Well I tried to answer some of the questions in my first post.. and you criticised & you seem to be making no effort to answer your own questions - so I can only assume you are trolling.
There are several problems with that auction - the things you mention are small things compared to not knowing at all what model the drive is. The manufacturers page will tell you for certain, exactly what the specs of the drive are.
Here is another tidbit you can add to your data bank (some sort of wiki would probably be appropriate for this - if it could possibly be arranged?):
Wide scsi (16 bit) can support 15 devices rather than 7 on narrow (8 bit) scsi. I think this was expanded in later versions of the scsi spec to support Logical Units, where each id can have 8 other devices connected - but for 68k mac purposes - 7 on narrow, 15 on wide.
The Atto IV and FWB SCSI Jackhammer are the only nubus boards I know of that have 68 pin (wide) connectors on them.
http://en.wikipedia.org/wiki/Comprehensive_SCSI_explanation
Edit away.
Update: Hmm that didn't work - deleted pretty quickly. Wonder why? Oh well there has gotta be a wiki around somewhere that can be used.
Yes... as you mentioned before. Look, I wasn't criticizing you... and the criticism isn't damning, or anything... and so what? I'm sure you're a good person and all... . I was trying (in vain) to prevent more posts of the same kind (even the old standbys are posting stuff that I was hoping to avoid), and I left the "voucher" still there for anyone to post anything they feel like... ah... nevermind... didn't mean to single you out or make you feel bad or anything negative.
Good stuff.
wikipedia....
You can wonder. I learned long ago that place is full of power freaks.
never going back to that planet...
Sorry Tom, I didn't click on the link on your post early in this thread. Yes, of course, that's probably what happened. He put the stats for an external drive in his listing. As anyone who's sold on eBay will tell you, making your auction listing can be very time consuming, and unfortunately, many sellers make shortcuts which also contain incorrect or misleading info that lead to big problems in the transaction. It's something you always have to expect on auction sites, so buyer beware. This thread is partly about that problem mixed up with the usual angst associated with dealing with the wide universe of SCSI.
CM, what is it exactly you want, help buying a drive, or someone to provide you with the perfect SCSI info page?
As to the former, we've tried to help with the example you mentioned. As for the latter, I haven't found it, nor do I have the time or inclination to do it for you (and, I expect, neither does anyone else here.) It looks as though you'll have to publish it yourself. Take what you know, add to it all the info you can glean from links provided above and give it another shot.
You might try it as a blog entry while in progress, that way you can edit as you learn more.
Edit: you also seem to want to know about specific drives, that's too large a subject for a single page. All the makers provide spec sheets online, when I need to know details that's where I go. If/when you build your own super-scsi page, if you like you can add links to the specs areas on the makers' sites.
dan k
No... I was using that auction as an example. Most drive auctions are similar. Its a real pain to do the kind of research necessary just to see if the item is something that you might want.
I was hoping to scare up interest in a mac users scsi guide, of sorts, a quick reference page that was — as far as the redundency of nomenclature, the different proticols, the different connectors, which macs used what, and what cards do what and with what — comprehensive.
no... not really. But I appreciate your input.