The following are selected from the users Forums at Deal Mac. Click to go to Deal Mac. Then click Forums at the top and search for topics (I used SCSI as my search item here). Wonderful place to get help! It takes some time to access because of the data base search - don't get "impatient"!

Topic: SCSI Terminology..Fast,Wide,Ultra-Wide,etc...
Name: HN (webproxy1.paging.mot.com)
Date: 09-14-98 16:17

Can someone please explain what SCSI-1, SCSI-2, SCSI-3, Narrow, Fast, Fast/Wide, Wide, Ultra-Wide, and any other SCSI terminology. What is the standard SCSI? How do the others rate as far in speed. Which can be adapted using...well, an adapter. Thanks.

Topic: RE: SCSI Terminology..Fast,Wide,Ultra-Wide,etc...
Name: RGM (wt-d4-208.wt.net)
Date: 09-15-98 06:25

The following varieties of SCSI are currently implemented:

SCSI-1: Uses an 8-bit bus, and supports data rates of 4 MBps

SCSI-2: 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.

Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit transfers.

Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data rates of 10 MBps.

Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 MBps.

Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20 MBps.

SCSI-3: Uses a 16-bit bus and supports data rates of 40 MBps. Also called Ultra Wide SCSI.

Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MBps.

Wide Ultra2 SCSI: Uses a 16-bit bus and supports data rates of 80 MBps.

Name: Derrick (cpb207.axion.net)
Date: 08-22-98 23:51

The external port, as you've surmised, is a Fast-SCSI port (more commonly known as SCSI-2 or "Narrow"). A Fast-Wide (commonly known as Ultra Wide or SCSI-3 Wide) drive will work on this port as long as you have the appropriate adapter to connect it. This adapter changes the 68-pin "Wide" interface into a 50-pin "Narrow" connector.

There will be a decrease in the Wide drive's transfer rate of data when it is connected to the external port. The Narrow port's maximum transfer rate is 10 MB/s. The Ultra Wide drive's transfer rate is 40 MB/s or more.

To realize the benefits of the Ultra Wide drive, you will need an Ultra Wide SCSI host adapter card, as you've also mentioned. Your 8100 has three NuBus slots. NuBus UW cards are somewhat rare and expensive, so you'll have to weigh the cost versus performance gain (and there will be a gain in performance!).

Name: Jon (pop188.city-online.com)
Date: 08-23-98 11:26

You will need a special cable which converts the wide drive to the narrow SCSI-2 cable. External cables are easily available; internal cables may be difficult to find. One source for external adapter cables is APS. Their web site is www.apstech.com. I have had very good service from them and their tech support is knowledgable.

Read the documentation/manual on your wide drive carefully for hints about running it on the varrow bus. There may be recommendations. If you don't have the docs, you should be able to find them on the web at the manufacturer's web site (unless the manufacturer happens to be Micropolis!)

A word about termination.

SCSI busses must be terminated at each end. Best way to do this is "active" or "auto" termination in which electronics does the job. However, some combinations of wide and narrow and internal and external drives demand that termination resistors be used. Try to stay away from getting too complex. The Macs primary interal drive (if SCSI, not IDE) is almost always terminated with termination resistors mounted on the drive, although if there is a SCSI CD-ROM, termination resistors will be on the drive which is last on the flat internal SCSI cable.

Easiest way to connect an additional internal drive is to connect the the new drive to the flat SCSI cable connector that is inbetween the last drive and the logic board. If you need to move the connectors to different devices, this is OK as long as you the same drive is last after you finish. Otherwise you must play the termination resistor game.

ALSO, you are better off getting a fast/wide SCSI card for NUBUS such as a JackHammer or ATTO Silicon ExpressIV. I have bought 1 each of these used from private individuals on the web with great success.

Why a wide SCSI card? BECAUSE, it is much easier and more sensible to go from a wide card to a narrow drive than vice versa.

Also, the 10MB/sec limit on NUBUS means that fast/wide NUBUS SCSI cards can never reach their potential of 20MB/sec. Than's just one reason why the newer PowerMacs use PCI.

FINALLY, make sure the SCSI ID on your wide drive is unique (different from the other SCSI drives on the same SCSI buss) to the SCSI bus and choose one that is between 0 (zero) and 6 (six) since the upper SCSI addresses 8-15 available to the WIDE drive are not seen by the narrow SCSI-2 system buss.

Make sure to take electrostatic shock precautions to protect the Mac.

SAD MAC? You probably got a duplicate SCSI ID which is the same as the boot drive. Could also be a bent or bad connector pin (they are rather tiny.) Can't see the drive after rebooting the Mac? Probably a bad connector or bent pin.

Hmmm. Long again. Probably more than you wanted to know.

Topic: RE: Ultra/Wide Scsi FAQ?
Name: Bob (a238.m4048-2.cmh-icg.infinet.com)
Date: 07-21-98 20:58

A fine base for information about cards and drives can be found in Mike Breeden's Accelerate Your Mac site http://www.xlr8yourmac.com/

Topic: SCSI, SCSI, SCSI!!
Name: Tone (syru218-206.syr.edu)
Date: 09-25-98 21:00

Hi. I may soon be in the market for a second internal hard drive for my PowerMac 7600/120. But I must admit, all these variations of SCSI confuse me a bit. My spec-sheet says that my Mac has "Fast SCSI" for its internal interface. So what kind of hard drives can I use with that. I assume I can't use "wide" SCSI, but what about "ultra" or "SCSI-3"? Some hard drives seems to have different capabilities based on which interface they're using, so I want to make sure I get the most out of my money. Any info on all this SCSI stuff would be greatly appreciated. And actually, while you're at it, if anyone has suggestions for a good, inexpensive 4 Gig hard drive, that'd be helpful as well. Thanks in advance.

Topic: RE: SCSI, SCSI, SCSI!!
Name: H.N. (user55.imagin.net)
Date: 09-25-98 21:50

i asked this question not too long ago...if you go to "search this forum" and type in "SCSI Terminology". You'll get the technical answer. FYI, your 7600 uses SCSI-2 or Fast SCSI (same). This is standard and won't be difficult to find a good deal on it. Go to: http://www.megahaus.com/ http://www.pdisales.com/ You can also search deal-mac.com for good deals too. GOOD LUCK!

Topic: RE: SCSI, SCSI, SCSI!!
Name: Tone (syru218-206.syr.edu)
Date: 09-25-98 22:27

I took a look at some old posts (sorry I didn't do so before making mine). There was a lot of good info. But one question still lingers in my mind - what kind of SCSI hard drive should I get? I know I have a Fast SCSI-2 internal interface, but I'm still not clear on what SCSI's are compatible with what. Is a Fast SCSI-2 Hard Drive the fastest I can get or can I get better performance with something else (with or without an adapter).

Basically what I'm asking is what 4 Gig internal hard drive would people suggest for my 7600?

Thanks again.

Topic: RE: SCSI, SCSI, SCSI!!
Name: Carl (spider-tk044.proxy.aol.com)
Date: 09-26-98 01:45

SCSI-3 (=ultra) drives are SCSI-1 and SCSI-2 (=fast) compliant. They will run at the speed of the your SCSI-2 bus. A 68 to 50 pin adapter will cut the data back to 8 bits; hence, there is no advantage unless you're planning to buy wide SCSI card at a future date. The best deal at the moment would be a 4.3 GB Seagate Barracuda from OWC for $269. Check it out. 7200rpm, 1024K buffer, 5 yr warranty. Why mess around?