Path: utzoo!mnetor!uunet!husc6!linus!philabs!sbcs!root
From: root@sbcs.sunysb.edu (SBCS Systems Staff)
Newsgroups: comp.sys.amiga
Subject: Re: SCSI Speed (was Re: FFS speed.  Bytes/Bits per s)
Message-ID: <1007@sbcs.sunysb.edu>
Date: 2 Mar 88 16:05:13 GMT
References: <8802251923.AA23029@cory.Berkeley.EDU> <3385@cbmvax.UUCP> <12330@orchid.waterloo.edu>
Organization: State University of New York at Stony Brook
Lines: 27
Summary: SCSI, and why you're not going to get > 3.579 mBytes/sec

In article <12330@orchid.waterloo.edu>, tdwest@orchid.waterloo.edu (Terry D. West) writes:
> I assume the 2090 cannot do Synchronous SCSI, but it would not be 
> difficult at ALL to build a 5 MBYTE/s (yes 5x10^6 8 bit chunks/second)
> synchronous SCSI host adapter for the amiga (I could do it in a weekend).  

	Terry, no problem building a 5 mByte/sec drive -> interface controller,
	but you won't get more than 14.318Mhz/(2*4) words (= 3.579 mBytes/sec)
	per second out of the Amiga bus.  This arises from the fact that
	you have to look like a 7.159 mHz 68000 when driving the Amiga bus,
	ie each word transferred takes 4 ticks of the cpu clock.  Of course,
	you could put a load of shared memory on the controller card and do
	your DMA to that memory, but that's another controversy :-)
	
> Undoubtably, there are SCSI drives out there that can do synch 
> (Adaptec's higher priced controllers can)... 

	I suspect that the only spindle you'll get more than ~3mByte/sec
	out of are the (still expensive) PTD drives that Fujitsu, etc
	make.  To the best of my knowledge, no one makes a PTD -> SCSI
	controller.

> Terry D. West
> 4B Computer Science/ Elec Eng
> watmath!orchid!tdwest

						Rick Spanbauer
						SUNY/Stony Brook