I'm not sure who this originally came from, but it's incorrect:

>> Can you tell me where to get a disk that will sustain a 5 Megabyte/sec
>> transfer rate (the speed of a SCSI bus)?  Also, the speed of the ISA
>> bus is 16 Megabytes/sec if you run it at 8 MHz (though you can usually
>> clock it at at least 10 or 12).  Thus, even with a 10 Megabyte/sec
>> fast SCSI controller, the ISA bus is still not the bottleneck.  You
>> might get slightly less CPU utilization while doing DMA's over ISA,
>> but I don't see how you can claim the bus is the throughput bottleneck
>> with recent disks.

The ISA bus (correctly clocked) maxes out at 8MB/sec.  It is a 16-bit
bus, and it takes *two* bus clock cycles per transaction.  Hence 8MHz
* 2 bytes / 2 cycles = 8MB/sec.

EISA and PCI burst modes take one cycle per transaction, at their
respective speeds.  But, as far as I know, even a single transaction
in non-burst mode on EISA and PCI take 2 bus clocks.

-----------------------------------------------------------------------------
  Michael L. VanLoon                                 michaelv@HeadCandy.com
       --<  Free your mind and your machine -- NetBSD free un*x  >--
     NetBSD working ports: 386+PC, Mac 68k, Amiga, HP300, Sun3, Sun4,
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     NetBSD ports in progress: VAX, Atari 68k, others...
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