Re: Mac HD #M0135

[shack@deimos.frii.com (Randy Shackelford)]

In article <5iu5dv$1pss@uni.library.ucla.edu>,
 <pubpc1@library.ucla.edu> wrote:

>>>SCSI may be SCSI, but there are several types of SCSI.  The one used
>>>most frequently in Apple II's in SCSI-II.  I think there's now a SCSI-III
>>>standard.  Of course, there is also SCSI-I, and SASI (pre-SCSI).
>>
>>Who told you that Apple IIs use SCSI-II? They can use the drives, but they
>>fall back to SCSI-I when  you connect 'em up to a SCSI card. Apple IIs are
>>not  fast enough to keep up with SCSI-I throughput so it would be utterly
>>pointless to implement SCSI-II on 'em.
>
>Read what he said, Randy.  He said that the one USED MOST
>FREQUENTLY in the II is SCSI-II, which is the truth of the
>matter since they pretty much don't make SCSI-I drives anymore.

When you say SCSI-II is most frequently used "in Apple IIs", to me it implies
that the interface is SCSI-II. I only have a HS SCSI card and it is only 
SCSI-I to my knowledge. I don't know whether there are any 68K Macs which use
SCSI-II for that matter. Guess I could pull out my 840av manual and check.
Notice I did say that SCSI-II drives work, but fall back to SCSI-I. The truth
of the matter is that no one makes <1 gig drives any more. So would you
conclude that everyone has a gig or more hard disk on their Apple II like
you conclude that everyone has a SCSI-II drive? I only recently moved up from
a 105 mb to a 230 mb myself.

>As for speed, the throughput of SCSI-I is theoretically 1MB/sec.
>That's the same as the maximum of the Apple bus.  SCSI-I's real
>world performance is somewhat worse because of noise and errors,
>so the II (with Apple II High Speed and RamFAST SCSI cards) can
>more than keep up.  There's no need to insult the Apple II.

I haven't tried asking it lately, but I don't think my IIgs is any
more easily insulted than any other inanimate object I own. Actually, my
'70 Chevelle convertible seems to be the most temperamental - if I take it 
out on a day too cold for its liking, it lets me know by running crappily.

Seriously, try this on for size: if I say that unidisk 3.5s have their own
processor and memory because 1 mHz Apple IIs are too slow to keep up with
the data, am I "insulting the Apple II" or stating a fact? Ditto for saying 
that SCSI on a //e is limited to 512K/sec.

>Implementing SCSI-II on the II would be good because it would
>eliminate incompatibilities with some CD-ROMs and hard drives.
>Remember how some SCSI-II drives won't work on the RamFAST?
>Also, a caching controller can accept data faster than the
>maximum of the computer's bus.  This is advantageous because
>data in RAM can be accessed faster (no R/W head positioning)
>than the physical hard disk.

How would I remember that? I have a HS SCSI and everything I've ever connected
to it with the exception of my magneto optical works.

>>>The HD20 may be SCSI-I or SASI.
>>
>>When I was looking to buy one, someone told me they use the MFM style hard
>>disk like PCs from the same era.
>
>The HD20 is like the other floppy port hard drives of the era,
>like the ProAPP series (10 or 20 megs).  The ProAPPs work with
>the //e and //c, though, while the HD20 will only work with a
>UDC.

I'll go along with that when I see it working. But I won't be volunteering
my HD20 for the test.
-- 
Randy Shackelford                                 
shack@frii.com