I've had enough! SCSI-2

[rezwits]

I don't care about wide or narrow or any of that old crap, or the throughput yada yada, I got all that.

I want to know when and which of the early macs went from SCSI to SCSI-2.

and/or Direct question:

Quadra 800: SCSI or SCSI-2

Quadra 840: SCSI or SCSI-2

Thanks guys, I keep looking this up and all I get:  "The story of SCSI" over and over, but I can't get ANY MAC SCSI specs, mind you I didn't hit archive.org, but the main problem is that's where all the Apple Documentation is (mostly).  Every time I look up a Mac, and it has SCSI all it will say is "SCSI" "SCSI", everymac and mactracker too.

Frustrating!

Laters...

 

[Elfen]

Stock Mac? From Apple?

With the exception of a couple of rare machines, none. They are all SCSI (SCSI-1) machines. There is a transition period where Macs went from SCSI to IDE and from IDE to ATA, and then to SATA but that's it.

PCI and NuBus cards that gave Macs SCSI-2 (and SCSI-Wide) abilities were mostly third party options.

 

[rezwits]

Thank you that's exactly what I wanted to know, (and thought), misleading lowendmac.com articles!

 

[johnklos]

SCSI is both a hardware and a protocol standard, which may explain why you see different things in different places. SCSI-2 was officially just a designation for the newer protocol, with Fast SCSI denoting synchronous transfers with updated timing specs which allowed for up to 10 MB/sec and Wide SCSI (16 bits), or the combination (Fast Wide SCSI).

To confuse things, SCSI-1 could be either asynchronous (up to 3.5 MB/sec, like many m68k Macs) or synchronous (up to 5 MB/sec).

The Amiga 3000, for instance, could operate in synchronous mode and because it ran using real 32 bit DMA, it was the fastest SCSI of its time. The Amiga was used to benchmark drives because it could operate at a full 5 MB/sec in 1990. Macs couldn't do that until Power Macs came out.

The PCI PowerMacs were the first Macs with SCSI hardware which supported Fast SCSI (10 MB/sec). Earlier Macs supported SCSI-2 commands but not SCSI-2 timing.

 

[NJRoadfan]

It gets better. The initial PCI PowerMacs all had TWO SCSI controllers on them. There was the internal MESH bus that ran at 10MB/sec and the external bus that ran at the standard 5MB/sec.

 

[trag]

The PCI PowerMacs were the first Macs with SCSI hardware which supported Fast SCSI (10 MB/sec). Earlier Macs supported SCSI-2 commands but not SCSI-2 timing.

Did the PM8100 not support 10 MBpS? It has a 53CF96 (not the 53C96) chip on board so it should be capable of supporting Fast SCSI unless Applle failed to implement something.

 

[gsteemso]

Unless I am misremembering, the 8100 IS one of the initial PCI Power Macs.

 

[Unknown_K]

8100 is Nubus along with the 6100, 7100 and 9150. 7500/8500/9500 were the first PCI Powermacs.

 

[trag]

For completeness and to avoid later confusion, it should probably be mentioned that the PCI Power Macs (x500 and x600 series) each had two SCSI busses.

The internal-only bus runs off Apple's "MESH" chip, which I suspect is just a licensed 53cf96, and supports Fast SCSI-2 operations.

The internal/external SCSI bus (one of the internal SCSI ribbon connectors is common with the external 25 pin connector) runs off Apple's CURIO chip which, among other things, apparently contains a 53c96 cell. This bus supports standard (slow) SCSI-2 speeds up to 5 MB/S.

So even on the PCI Power Macs, not all SCSI is Fast SCSI.

All Apple SCSI busses which have an external connector are slow. For example, the Beige G3, which is newer than the x500/x600 series, only has slow. It was only on internal-only busses that Apple dallied with Fast SCSI.

 

[johnklos]

The distinction is that the first time that Fast SCSI was available on Mac motherboards was with the (I stand corrected) Power Mac 8100. All the non-IDE PCI Power Macs supported 10 MB/sec Fast SCSI. Note I didn't say that they ONLY support Fast SCSI.

 

[rezwits]

Nice round up guys!  Gees, this was just a mess, and now I know why the sites don't get into the "Sticky" details...

(On a side note I did remember the SCSI internal was 10 MB and the external was 5 MB, which I always thought was weird!)

Thanks I really appreciate all these notes cause now I can make the best upgrade decisions...

Laters...

 

[trag]

The distinction is that the first time that Fast SCSI was available on Mac motherboards was with the (I stand corrected) Power Mac 8100. All the non-IDE PCI Power Macs supported 10 MB/sec Fast SCSI. Note I didn't say that they ONLY support Fast SCSI.

NITPICK The PM7200 does not support Fast SCSI. It has the CURIO chip, but no MESH. /NITPICK

It's an interesting case because it is an extremely similar architecture to the x500 machines and even uses the same ROMs.

Many of Power Computing's clones were based on the 7200 (Catalyst) and word wss that PCC wanted to add Fast SCSI to one or more of their Catalyst clones but couldn't clear it with Apple. I'm not sure how much control Apple really had other than refusing to sell MESH chips. I wonder if that means that just putting a 53cf96 there wouldn't work.

 

[johnklos]

Good to know about the 7200, trag!

I remember reading about someone who soldered a 53CF96 in place of a 53C96 in a Quadra 950:

https://groups.google.com/d/msg/vintage-macs/NnXaM1eHqUA/WQY9oqFFr8gJ

While it'd be best to modify the ROM to enable Fast SCSI, it could also be done with the system running.

Other machines were also upgraded from the very common NCR53C94 to 53CF96. For instance, the VAXstation 4000/90 or 96 could be upgraded by a company that also increased the cache size and quadrupled the size of usable SIMMs. They included an updated firmware image (that model had FEPROMs so the firmware could be easily updated) that configured the bus to run at the full 10 MB/sec.

 

[Powertrip]

This stuff is crazy interesting to a guy who is intimidated by soldering and board level repair and upgrades.

And it is so very cool to have people with this knowledge and talent in our community!