🚀 go-pugleaf

In article <8774@spool.cs.wisc.edu> shekita@provolone.cs.wisc.edu (Eugene Shekita) writes:
>
>From what I've read over the net, the way I view a typical SCSI configuration
>is as follows:

Should be more like:

>
>    -------------      ----------
>    | Processor |      | Memory |
>    -------------      ----------
>          |                |
>     ==================================   Main Bus
>          |
>     -------------------    -------
     |Host Adapter or    |
     |File Processor     |
      -------------------
           |
           |--------------|-------------|-------etc.
    ---------------   ------------   ----------------
   |Disk Controller| |Tape        | |Disk Controller |
    ---------------  |Controller  |  ----------------
     |                ------------       |
     |--Disk Drive     |                 |--Disk Drive
     |                 |--Tape Drive     |
     |--Disk Drive                       |--Disk Drive
     |                                   |
     etc.                                etc.

>
>   1) How does DMA logic get added to the picture -- is it typically
>      a separate unit with its own buffer, thereby allowing full-word
>      transfers over the main bus instead of 8-bit SCSI words (ala Amiga)?
>      Or do DMA units typically have no buffer?

DMA logic along with buffers and/or file processing software resides 
on the file processor.  This also allows effecient matching of SCSI
transfer rates to the system bus transfer rate.  Of course not all
systems contain all of the hardware options to configure something this
extensive, depending upon the speed and price of the system.

>
>   2) Dual-ported memory systems let DMA transfers go straight into memory 
>      without tieing up the main bus, right? Roughly, how much cost does
>      a dual-ported memory system add, and is that why they're usually only
>      found on *big iron*? And while we're at it, what level of multi-porting
>      do some of these *big iron* machines have (a Cray, for example)?

Not neccessarily.  There are a lot of different reasons why you might or
might not want to use dual ported memory and why you might or might not
want to use the side opposite the processor for IO operations.  Keep in mind
there are a lot of different classes and application types of machines.
"Big Iron" does not neccessarily imply a Cray.

>   4) Is it becoming common for SCSI controllers to have a track-size 
>      buffer of their own and always do track-size reads? (I am told 
>      that Conner contollers have this feature.)

Yes, as well as various forms of caching.  SCSI used on "Big Iron" will
probably have from 2 to 200 Megabyte of buffer space, depending upon the
type of usage.


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                                   Don Sleffel
                                   3718 N. Rock Rd.
                                   Wichita, KS  67226
                                   

                                                                  

<d.sleffel@Wichita.NCR.COM>                                     
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