info-mac@uw-beaver (info-mac) (07/19/84)
From: Karl B. Young <KARLB@SU-SCORE.ARPA>
I have seen both the Tecmar and Davong hard disk systems. Neither one of them
use the AppleBus protocol although they both use one of the ports out the
back of the Mac. Both drives supply an external clock to the Zilog SCC
chip so that it can run at a faster rate than the AppleBus standard of
230.4 Kbaud (the Tecmar runs at around 700 Kbaud, the Davong at around 810
Kbaud).
Both of these drives fall into a category of devices called "direct connect
devices". The ports that they connect into are dedicated to servicing
the drive and cannot be shared with any other device. To be precise, the
Tecmar device tries to get around this limitation ("use a drive, lose a port")
by providing another DB9 port on the drive which can allow signals to "pass-
through" the drive under certain circumstances. I don't know how or how
well this works. In any case, even this does not provide for a true "shared
peripheral bus" such as AppleBus.
By the way, either port out the back can be used as an AppleBus port. It is
strictly up to the software driver.
From personal experience, any hard disk on a Macintosh is a joy to behold.
Even slower drives (such as Tecmar appears to be) seem fantastic--the true
advantage of hard disks is their large capacity, and any added speed is
just an added delight.
Karl B.
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