Fastlane card and SCSI

[macce2]

The Fastlane card has a Centronics style connector for connecting external SCSI drives.
If I had some external SCSI drives with SCSI-2 style connectors, could I use some proper adapter part (or cable) and still have full SCSI-2 speed ( and all the other benefits of SCSI-2 standard, compared to-1), If my external drive(-s) support it ?
So, does using (SCSI-1) Centronics to SCSI-2 connector " downgrade" my SCSI bus performance/ stability somehow ?

[mech]

An adapter will work fine. You can go from Centronics 50 to typical high density 50 scsi 2 connectors with no problems.
there will be no speed loss or reliability problems.

[macce2]

Oh, thats what I assumed, but wasnt sure.The number of pins is the same 50(?!).
However, I read there are some bad quality SCSI cables out there, and proper quality cabling is important in terms of SCSI.

Thank you for helping me, mech !
Ps. Coulnt find the answer from old SCSI faq.

[alewis]

OK, minor point to get out of the way: nothing uses SCSI-1 it has been dead since about 198something.

The 50pin SCSI connector is -strictly speaking - the best quality interface to use; all 50 pins are connected, including ground. Apple introduced a 25pin connector, which ties all the grounds to a single pin. Not a great idea. In the real world it doesn't make any difference until you have a problem, then it is a sod to diagnose as you can't rule the cable/connector out.

50-25 pin adaptors, or more commonly cables, are plentiful. Using one will not affect your throughput (or 'speed'). Unless the cable is at fault; then generally it will either not work, or you will see issues with devices not appearing, or hanging when read/written to.

The number of pins does not identify the SCSI version. E.g.

SCSI-1 and 2 use a 50pin connector. Fast-Wide SCSI-2 used two cables...

SCSI-1 and 2 use a 'narrow' bus - 8bytes but...a 68pin connector does not mean SCSI-3; the SCSI-2 Ultra-Wide interface uses a 68pin interface (16bit, 40Mhz).

The Fastlane uses a SCSI-2 8bit bus @ 10MHz, it is a not a SCSI-1 interface. With the correct cable (Centronics 50 to DB25?) you should have no problems.

Can't identify if the cable is good? It should be quite thick. If it is thin, then only 1 pin is being taken from the C50 port as ground. A thick cable will run all ground pins to a single pin on the DB25 end, which whilst not ideal, makes for a better cable.

[macce2]

Oh, I got my Scsi setup up and running, but currently do only have 4 Mb Ram added to my Fastlane card.
The question is: How much would I benefit from adding some more, maybe the max 64 Mb to my card ?
Considering transfer rates and general performance ?!
I do have BigRamPlus card installed, but guess the Ram added to Fastlane card would be noticeably faster ?

[Jope]

Originally Posted by macce2

I do have BigRamPlus card installed, but guess the Ram added to Fastlane card would be noticeably faster ?

I'd wager it is the same speed for both cards. The Zorro III bus is what will be the bottleneck here.

[macce2]

I assumed that if I added the full 64 Mb Ram to the Fastlane card, and then maybe totally removed the BigRamPlus card, my Scsi setup ( maybe whole system ?!) would perhaps be somewhat faster/ better ..?!

[grelbfarlk]

Originally Posted by macce2

I assumed that if I added the full 64 Mb Ram to the Fastlane card, and then maybe totally removed the BigRamPlus card, my Scsi setup ( maybe whole system ?!) would perhaps be somewhat faster/ better ..?!

Not really, the Fastlane will have lower priority than the motherboard memory. When the motherboard RAM runs out it will use the next lower priority RAM, at that point SCSI *might* speed up.

Though you can test with this:
http://aminet.net/package/util/cli/ChangeMemPri
Change the Fastlane memory so it has higher priority than the motherboard. The SCSI should speed up noticeably but the CPU will be a little bit slower. You could also try raising the BigRamPlus priority over the motherboard memory for testing, but you need to do this early in startup-sequence before all of the libraries are already loaded into the motherboard RAM.

With an A4091 and a 3128, raising the 3128 priority above the motherboard memory will increase the A4091 speeds significantly. Same with Fastlane, however raw benchmarks will show PIO mode is actually faster than DMA mode in transfer rate at least. However you probably want DMA mode so as not to make the CPU do all of the moving around.

I think the effect is the same with all Z3 RAM but I've never tried this with the BigRamPlus, so you should try it and see.

Test with Sysspeed and RSCP and we can compare results.

[macce2]

I' m currently testing with ChangeMemPri program; but noticed I must boot without startup- sequence, to make it work. Is it possible to save the changed, new priorities somehow; or is it executing ChangeMemPri in startup the only way ?
With MMUlibs installed, I guess I' d better edit the MMU configuration file (?!) , but how ??

[grelbfarlk]

You can't "save" the changed priorities as they are getting plopped in place by whatever mechanism is initializing the memory, autoconfig, ROM or whatever. You should be able to make the change in the startup sequence but that's probably dicey as setpatch isn't going to like putting kickstart modules in Z3 space. But even if you don't do it during startup, you should be able to change the priorities when Workbench is up, it just might not be really "fair" since some of workbench will be loaded in the motherboard RAM.

[macce2]

Back to the main topic;

Which would be the optimal Ram speed for a Fastlane card memory upgrade; maybe 50 or 60 ns Ram ?

[grelbfarlk]

The Fastlane can go as fast as 40ns, but those are going to be hard to find, so reasonably 60ns.

[macce2]

Ok, I had some problems with my new 16 Mb simms for the Fastlane card, and I decided to experiment a little and disabled the Fastlane card memory with the jumper settings.
I do have BigRamplus card installed.
According to Sysinfo, no decrease on file transfer speed(s)..
Is it of any particular reason for me to keep some Ram added to my Fastlane card ..?
(The memory I removed was 64 mb, but seen only as 40 mb; and it was 60 ns memory)