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Old 30 March 2018, 12:24   #1
Sim085
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(SCSI to IDE to CF) vs (IDE to CF)

As we all know the A500 did not have either SCSI or IDE connectors while the A1200 came with an IDE connector.

For the A500 I have an expansion which provides a SCSI connector. I then have a SCSI->IDE adapter and an IDE->CF adapter. For the A1200 I just have an IDE->CF adapter.

However on another post I read that SCSI is better than IDE because IDE eats up a very large percentage of CPU time for disk I/O while SCSI has DMA and eats less CPU time.

So my question is; since at the end I am using CF cards then does it make a difference having SCSI or not?
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Old 30 March 2018, 12:40   #2
Toni Wilen
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Which A500 SCSI controller? Most A500 SCSI controllers are not DMA. Main (and also popular) exceptions are Commodore A590 and GVP Series II.
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Old 30 March 2018, 12:45   #3
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You're asking the wrong question here imo, are you using your Amiga for anything that is going to notice lost cpu time while accessing disks? I suspect the answer will be no unless you are using audio programs to make CD quality sound tracks and things of that nature. Games playing probably doesn't even tickle the cpu when they are accessing disks and most programs on the Amiga are tiny and load in a blink of an eye.
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Old 30 March 2018, 14:18   #4
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Grand Slam 500
http://amiga.resource.cx/exp/grandslam500

Quote:
Originally Posted by Toni Wilen View Post
Which A500 SCSI controller? Most A500 SCSI controllers are not DMA. Main (and also popular) exceptions are Commodore A590 and GVP Series II.
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Old 30 March 2018, 14:20   #5
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To be honest anything I ask is mostly theoretical not because of use. I would say my question is more of the sort; since at the end of the chain there is a CF card, would SCSI still be better than IDE?

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Originally Posted by -Acid- View Post
You're asking the wrong question here imo, are you using your Amiga for anything that is going to notice lost cpu time while accessing disks? I suspect the answer will be no unless you are using audio programs to make CD quality sound tracks and things of that nature. Games playing probably doesn't even tickle the cpu when they are accessing disks and most programs on the Amiga are tiny and load in a blink of an eye.
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Old 30 March 2018, 14:26   #6
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If you have a DMA-capable SCSI controller, then that will offer lower CPU usage during transfers than CPU-driven IDE solutions, resulting in a smoother experience and faster drive access in certain use conditions. That string of adaptors though will cost you a small fortune these days though, so it comes down to whether it's worth it for what it probably an insignificant difference in practice.
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Old 30 March 2018, 15:44   #7
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You can just as well skip the IDE bridge and use a SCSI2SD instead.
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Old 30 March 2018, 20:28   #8
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Agreed with idrougge. For most regular users the approx £55 SCSI2SD v5 would be more than capable for general use. I think I got 1.1mb/s out of the V5 on an A3000. The SCSI2SD v6 is faster (1.8mb/s i think on an A3000) but more expensive at approx £95. SCSI to IDE stuff like the Acard AEC 7720UW is now rare and expensive and only necessary to get maximum performance out of Ultra Wide SCSI setups (20+ mb/s), on an A3000 a 7720UW manages about 1.9mb/s.

I dont know anything about A500 SCSI cards (I only have experience of SCSI on the A3000 and the A1200 with a Blizzard 1260 SCSI kit) but I guess anything over the SCSI2SD v6 is overkill.

Last edited by trixster; 31 March 2018 at 15:10.
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Old 31 March 2018, 14:10   #9
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What I mean is does SCSI with DMA still offer any advantage when the end medium is a CF card and not a mechanical disk?

i.e. between:

(a) "SCSI (with DMA) -> CF"
(b) "IDE -> CF"

Does (a) still provide any real advantage on (b)?

I understand that with DMA the CPU is immediately free to work on the next thing, but given CF cards are faster than mechanical disks then I would expected that with a CF card the CPU will be able to move much quicker to do the next job.

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You can just as well skip the IDE bridge and use a SCSI2SD instead.
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Old 31 March 2018, 15:09   #10
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Entirely anecdotally: I can't really tell the difference in HD access speed between my three amigas. My A4000 is currently using the on-board IDE -> CF adapter. My A3000 is using the on-board SCSI (which has DMA I think) -> SCSI2SD v6. My A1200 is using on-board IDE -> IDEFIX Express -> CF Adapter (the IDEFIX EXpress returns about 3.8mb/s). When I use the Blizzard 1260 SCSI the file access if noticeably quicker but I can't really notice whether the system responds any snappier due to using SCSI as the 060 makes the system already more than fast enough.

With an Amiga the bottleneck is always likely to be the interface; whether you're using a physical hard disk or a CF card probably matters not, as both have more than fast enough access and read speeds to cope with the tiny files an Amiga normally works with.

For regular use I doubt whether you could measure the difference in system load or performance (which is to say, whether the system lags or loses responsiveness) between a system with CF card -> SCSI DMA, and a system with mechanical HD -> SCSI DMA.

Last edited by trixster; 31 March 2018 at 15:16.
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Old 31 March 2018, 15:32   #11
Toni Wilen
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A3000 SCSI should have over 6MB/s transfer rate, it looks like you haven't set it to sync mode (async probably is max 2.5MB/s or so)

I agree that A500 with or without DMA does not make much difference in real world use, at least without accelerator that has both onboard fast ram and onboard IDE or SCSI.
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Old 31 March 2018, 15:58   #12
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My two cents. I had the scsi to sd adapter in my A2000 and would only get 1mb per sec speed. That is supposedly all you will get with that device.
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Old 31 March 2018, 17:07   #13
trixster
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Quote:
Originally Posted by Toni Wilen View Post
A3000 SCSI should have over 6MB/s transfer rate, it looks like you haven't set it to sync mode (async probably is max 2.5MB/s or so)
Interesting to know! I've only had the machine a short while so I'm still playing with it. I'll test sync/async modes. Thanks Toni
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