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From: c152-cb@cory.Berkeley.EDU (Vince Lee)
Newsgroups: comp.sys.amiga
Subject: Re: Hard drive & chip contention
Message-ID: <11072@pasteur.Berkeley.EDU>
Date: 14 Mar 89 17:54:34 GMT
References: <8903071906.AA01731@jade.berkeley.edu> <796@zehntel.UUCP>
Sender: news@pasteur.Berkeley.EDU
Reply-To: c152-cb@cory.Berkeley.EDU.UUCP (Vince Lee)
Organization: University of California, Berkeley
Lines: 23

In article <796@zehntel.UUCP> donw@zehntel.UUCP (Don White) writes:
>In article <8903071906.AA01731@jade.berkeley.edu> GIGUERE@WATCSG.BITNET (Eric Giguere) writes:
>>The local Amiga dealer here is very reluctant about selling me a SCSI
>>drive for my 2000 because he claims that anything more than 2 bitplanes
>>causes mucho contention between the drive and the Amiga's graphics chips
>
>     The SCSI interface has NOTHING TO DO WITH THE GRAPHIC CHIPS!!!!
>
>     I don't know where your dealer heard this, but is false. There may have 
>     been something wrong with the SCSI (broken, misjumpered, whatever). But
>     there is NO INHERENT problem with using one in an amiga.

Well, your dealer is wrong, but I think i know where he is coming from.  the
problem lies not in scsi itself, but in commodore's 4090a scsi controller.
The 4090a is dma.  In a hires 4-plane screen, or other graphically intense
display, there aren't enough dma slots left for the controller to do decent
dma.  I believe (correct me if i am wrong) that there is a flaw in the current
driver software which causes the data to queue up incorrectly b/c of this.

Anyway, there is no problem with scsi using other 3-rd party non-dma
controllers such as gvp.  They're also cheaper, but most will not handle 
st506 drives.  If you don't need st506 drives, i would go ahead with one of
them.