Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!lll-winken!sun-barr!newstop!sun!basselope!shiffman From: shiffman%basselope@Sun.COM (Hank Shiffman) Newsgroups: comp.sys.mac Subject: Re: Another type of interface card? Message-ID: <125809@sun.Eng.Sun.COM> Date: 4 Oct 89 20:36:28 GMT References: Sender: news@sun.Eng.Sun.COM Reply-To: shiffman@sun.UUCP (Hank Shiffman) Distribution: na Organization: Sun Microsystems, Mountain View Lines: 36 In article storkel@rudist.shell.com (S. Storkel) writes: >Why couldn't someone >have designed things so that there were at most three types of >interfaces (best bet: SE/30 and Mac Portable sharing the same type >of interface). Sure it would have been a little bit more complicated, >but I think the payoffs would have been well worth the effort. Where >am I missing the boat? At a guess, I'd say you're assuming a level of processor compatibility between the 68000 and 68020/30 that doesn't exist. There are a lot of extra pins on the PDS for the SE/30 that don't exist on the SE. They're there because the SE has a 16 bit data path and the SE/30 has a 32 bit path. The Portable, like the SE, has a 16 bit path. So to be compatible with the SE/30 it would need a bunch of extra logic to take the 32 bit wide data coming in from the bus and ship it to the processor in two clock cycles, reversing the process for data going the other way. As to why the SE and the Portable can't use the same bus, there may be a number of reasons relating to the difference in clock rate, bus communication with the other slots in the Portable, power or cooling requirements or some other aspect of the Portable's architecture which make the simple approach taken on the SE unacceptable here. Finally, there may have been packaging problems involved in making the same size and shape space available inside the Portable as in the SE or SE/30. Any combination of these might have required the Portable to use yet another incompatible slot design. -- Hank Shiffman (415) 336-4658 Marketing Technical Specialist Software Engineering Technologies ...!sun!shiffman Sun Microsystems, Inc. shiffman@Sun.com