SCSI vs SASI
Jeffrey Samosir
Hi,
Does anybody know the differences between SCSI and SASI?
Can I access SASI drive with SCSI controller?
Thank you.
Jeffrey Samosir
Lupe Christoph
tri...@melsa.net.id (Jeffrey Samosir) writes:
>Does anybody know the differences between SCSI and SASI?
>Can I access SASI drive with SCSI controller?
SASI (Shugart Associates Standard Interface, I believe) predates
even SCSI-1. But when I had a SASI device a long time ago, it
worked on the SCSI host adapter of a Sun-3.
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Hennes Passmann
Lupe Christoph (lu...@alanya.m.isar.de) wrote:
: tri...@melsa.net.id (Jeffrey Samosir) writes:
: >Does anybody know the differences between SCSI and SASI?
: >Can I access SASI drive with SCSI controller?
: SASI (Shugart Associates Standard Interface, I believe) predates
System
: even SCSI-1. But when I had a SASI device a long time ago, it
: worked on the SCSI host adapter of a Sun-3.
I could try to give a short anwser, but the question keeps popping up, so
I have compiled a short history of SCSI below. I hope that by posting this
rather then mailing it directly towards you the people on this group will
point out any errors in the text below.
#include <stddisclaimer.h>
1979 The diskdrive manufacturor Shugart begin working on a new drive
interface with logical rather then physical adressing.
6 byte commands.
Shugart Associates Systems Interface (20 pages long) made public.
<SASI drives>
1980 Attemp to make SASI an ANSI standard failed.
1981 Shugart and NCR request an ANSI committee be formed for SASI
1982 ANSI committee X3T9.2 is formed.
1983 <Production of SCSI-1 drives>
1985 CCS (Common Command Set) used in most diskdrives
1986 Work begins on SCSI-2
1986 SCSI-1 becomes official as ANSI X3.131-1986
(yes, after the work had begun on SCSI-2)
6 and 10 byte commands.
<Production of SCSI-2 devices>
1994 SCSI-2 becomes official as X3.131-1994
SCSI-2 is backwards compatible with SCSI-1 and adds the following:
*Fast SCSI-2. Optional busspeed of 10MHz instead of 5Mhz.
*Wide Optional 16 or 32 bit cable instead of 8 bits.
*more commands defined, many optional (I'm not going to type the
entire list here)
*broader support for non-disk devices (tape.CDROM,Scanners....)
SCSI-2 devices can talk to the hostadaptor on there own inititive.
(e.g. to set in which mode they shoud operate, fast or not, wide,
extra wide or normal ...) This can confuse some older SCSI-1 HA.
<Production of SCSI-3 drives>
Ultra SCSI: Busspeed of 20Mhz?
Now: SCSI-3 proposals include:
-Support for graphical commands.
-Fibre channel protocol (fibre channel)
-Serial packet protocol (IEEE P1394)
-SCSI-3 general packet protocol (almost all serial interfaces)
and ofcouse the old SCSI-2 commands and more.
Future: SCSI-3 becomes official
Some aditional usefull terms:
-----------------------------
-Hostadaptor:
The card that connect your computer to the SCSI-bus.
Usually called SCSI-controller by markingtroids.
-Terminators (passive).
A group of resistors on the phsical end of a single ended SCSI-bus
(and only on these ends) that dampens signals on the bus. This
prevents the signals from bouncing at the end of the cable.
Each terminated signal is connect by:
* 220 Ohm to +5 volt (TERMPW)
* 330 Ohm to ground.
The 18 signal that are terminated are:
I/O, Req, C/D, Sel, Msg, Rst, Ack, Bsy, Atn, DB(p), DB(7) ... DB(0).
-Terminators (active).
Rather then passive terminators that use TERMPW which may not be
exactly +5v active terminator use a voltage regulator.
-Single ended:
"Normal" electrical signals. Uses open connector to the SCSI bus, [usually]
survives wrong cable insertion. The max. length for SCSI-1 is a 6 meter
cable with stubs of max 10cm allowed to connect a device to the main-cable.
Most devices are single ended.
-Differential:
Uses two cables to drive one signal.
Max. cable lenght of 25 meters.
Electrically incompatible with single ended devices!
SCSI-1 and upwards.
-Apple kludge:
The single ended 50 pins cable has been reduced to 25 pins by
tying all grounds toghetter. DB25 connector (like a paralel port).
Often used as the external SCSI connector.
-Asynchronyous SCSI:
A way of sending data over the SCSI-bus.
The initiator send the command over the bus and then waits until
it receives a reply (e.g. an ACKnowledge).
All commands are send asynchronyously over the 8 bit part of the
SCSI-bus.
-Synchronyous SCSI.
Rather then waiting for an ACK devices that both support synchronyous
SCSI can send multiple commands over the bus in the folowing way:
send data : send data : ... : send data (max outstanding messages)
: wait : wait : respons 1 : repons2: ...
This inproves throughput,especially if you use long cables.
(The time that a signal travels from one end of the cable to the other
end of the cable IS relevant.)
-Fast SCSI:
Fast SCSI allows faster timing on the bus. ( 10MHz instead of 5MHz )
On a 8 bits SCSI-bus this increases the *theoritical* maximun speed
from 5MB/s to 10MB/s. I know no single drive that reaches these speeds.
-Ultra SCSI:
Allows upto 20Mhz signals on the bus.
-Wide SCSI:
Uses an extra cable to send the data 16 or 32 bits wide.
This allows for double or quadrupple speed over the SCSI-bus.
Note that no *single* drive reaches these speeds, but groups
of several drives can.
PS: Sorry for the many typos,English is not my native language.
-Hennes
hen...@stack.urc.tue.nl
Helling Bernie
In article <4rr0o6$g...@tuegate.tue.nl>,
Hennes Passmann <hen...@stack.urc.tue.nl> wrote:
>Lupe Christoph (lu...@alanya.m.isar.de) wrote:
>: tri...@melsa.net.id (Jeffrey Samosir) writes:
>
>: >Does anybody know the differences between SCSI and SASI?
>: >Can I access SASI drive with SCSI controller?
>
>: SASI (Shugart Associates Standard Interface, I believe) predates
> System
>: even SCSI-1. But when I had a SASI device a long time ago, it
>: worked on the SCSI host adapter of a Sun-3.
>
AHA! I am a scsi novice, but I do know a bit about SASI, or rather how to
fake a SASI drive......
This is more properly in the land of 8 & 16 bit Atari's, but
ADAPTEC made an evil MFM (or RLL) => SCSI bridge adapter board that was
popular many moons back when scsi drives cost far more than the mfm/rll
versions...
A jumper on this card makes it behave like a SASI drive...
I use one to give scsi to an ancient Mac plus with a full height 60 M mfm
run as a 90M rll => scsi. Curiously enough, other diagnostic software sez
I have a sasi drive....
Adaptec 4000A and 4070A (rll)
The cards still float around... and If you have a SASI drive,
stick it in an XT case, put it under the Mac Plus and format it with D/IO
software (or others)....
Jeesh... whatta hobby...
B/H.
Don Yuniskis
>-Terminators (passive).
> A group of resistors on the phsical end of a single ended SCSI-bus
> (and only on these ends) that dampens signals on the bus. This
> prevents the signals from bouncing at the end of the cable.
> Each terminated signal is connect by:
> * 220 Ohm to +5 volt (TERMPW)
> * 330 Ohm to ground.
> The 18 signal that are terminated are:
> I/O, Req, C/D, Sel, Msg, Rst, Ack, Bsy, Atn, DB(p), DB(7) ... DB(0).
>
>-Terminators (active).
> Rather then passive terminators that use TERMPW which may not be
> exactly +5v active terminator use a voltage regulator.
Argh! I *really* hate the terms "active" and "passive" as applied to
SCSI terminators (but I won't climb on my soap box!)
The so called "active" terminators are really *series* terminations.
TERMPWR is fed into a low-voltage (~2.95V) regulator. A resistor
connects this synthesized voltage to the signal line. This terinator
represents the Thevenin equivalent of the "passive" terminator. I
suspect it has adopted the name "active" because the terminator contains
the low voltage regulator -- an "active" component.
Then, there's Forced Perfect Termination...
--don
cjbrown
On Tue, 9 Jul 1996, Helling Bernie wrote:
> In article <4rr0o6$g...@tuegate.tue.nl>,
> Hennes Passmann <hen...@stack.urc.tue.nl> wrote:
> >Lupe Christoph (lu...@alanya.m.isar.de) wrote:
> >: tri...@melsa.net.id (Jeffrey Samosir) writes:
> >
> >: >Does anybody know the differences between SCSI and SASI?
> >: >Can I access SASI drive with SCSI controller?
> >
> >: SASI (Shugart Associates Standard Interface, I believe) predates
> > System
> >: even SCSI-1. But when I had a SASI device a long time ago, it
> >: worked on the SCSI host adapter of a Sun-3.
> >
>
> AHA! I am a scsi novice, but I do know a bit about SASI, or rather how to
> fake a SASI drive......
...
> Jeesh... whatta hobby...
> B/H.
We still support SASI devices. We use the NCR53C80 and AMD5380 SCSI bus
controller chips on custom boards to control SASI tape drives.
Christopher Brown, Brown Computer Company, Research Triangle Park,
North Carolina 27709-3381 USA, +1 919 361 5118 voice, +1 919 544 8970 fax