Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!beach.cis.ufl.edu!scroll
From: scroll@beach.cis.ufl.edu (Steve Croll)
Newsgroups: comp.sys.amiga
Subject: Question on hard-drive interfaces.
Keywords: DMA interface hard-drives
Message-ID: <21058@uflorida.cis.ufl.EDU>
Date: 16 Oct 89 02:51:05 GMT
Sender: news@uflorida.cis.ufl.EDU
Reply-To: scroll@beach.cis.ufl.edu ()
Organization: UF CIS Department
Lines: 45


    In the next few months I will be purchasing an Amiga 2000 along
    with a hard-drive interface.  My question is whether the interface
    should be DMA or non-DMA.  I assume a DMA interface would be more
    efficient on a multitasking system.  Raw transfer speed by itself
    is not necessarily good if it eats all the CPU's cycles (and
    leaving little for other programs running in the system).
    
    A few days ago I was talking with a dealer in the St. Petersburg
    (Florida) area.  He strongly recommended I should NOT buy a DMA
    interface for the following reasons:
    
        * It can be very slow during high DMA activity (such as having
          a high-res interlaced 16-color screen).
          
        * It can cause the machine to "lock-up" (be trapped in an
          infinite loop) during high DMA activity.  He described an
          example on an Amiga 2500 running Deluxe Paint.  He said that
          in a high-res interlaced 16 color screen, the machine will be
          "stuck" in an infinite loop if you tried to save the current
          screen to hard disk.  He said the only way around this is to
          quickly switch screens using the left-Amiga-n combination
          right after "save" was selected.  He also said he had
          similar troubles with other (unnamed) DMA interfaces.
          
        * Commodore has verified the above "lock-up" problem and
          correspondingly their new interface will NOT do DMA.  He
          cited Supra Corporation's decision to move from a DMA
          to a non-DMA type interface.  
          
    How much of the above is true?  I know Commodore's 2090(A)
    controllers are horribly slow when there is high DMA activity, but
    from what I have heard it is attributed to "poor" design rather
    than an inherent flaw in "doing" hard-disk DMA on an Amiga.  Is
    there really such a problem with DMA style interfaces?
    
    Thank you for your time.
    
    

    
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Steve Croll (email: scroll@beach.cis.ufl.edu  home: 904-373-8389)