Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!nosc!ucsd!rutgers!gatech!sbmsg1!scbhq!uahcs1!madhat!alvitar From: alvitar@madhat.UUCP (Phil Harbison) Newsgroups: comp.sys.ibm.pc Subject: Re: NuBus Message-ID: <273@madhat.UUCP> Date: 5 Jul 88 20:49:59 GMT References: <26.22CD76D1@ankh.UUCP> Organization: DataVision, Huntsville AL Lines: 31 In article <26.22CD76D1@ankh.UUCP>, Frank_Hill@ankh.UUCP (Frank Hill) writes: > I heartily agree that the MCA buss should *NOT* be endorsed. ... The > TI NuBus ... would provide an ideal buss architecture ... I fully agree with Frank. I've designed cards for several busses (VME, PC/AT, Q-Bus, MultiBus) and thoroughly researched most of the others (except FutureBus). NuBus is clean, simple, and processor independent. It supports automatic configuration with features like geographic addressing and identification PROMs. NuBus uses distributed arbitration and directed interrupts, so there are no daisy-chain signals. The only centralized services are the reset and clock logic, and there are ways to distribute even those resources. NuBus uses a multiplexed, 32-bit address and data bus, with maximum bandwidth of 37.5 MegaBytes/second. The data bus is unjustified, so there is no need for byte swapping logic except on the CPU card, where it belongs. Nubus also provides a "try-again-later" response to a memory cycle, making it easy to build adapters to other busses, or implement cache coherency schemes. The new form factor used in the MacII (4.0" by 12.8"), is slightly smaller than the size of the AT-bus cards (4.8" by 13.12"). Systems built around this form factor could probably use the rash of existing cheap PC enclosures. If the 386 PCs use NuBus, then third party hardware vendors can build a single product for both markets. NuBus uses the 96-pin DIN-41612 connectors, which are more reliable than the edge connectors used on the AT and the MCA. Pin density is 1.5 times that of the connector used in the AT, and about the same as those used in the MCA. The connector is located closer to the center of the board (about 3 inches from the end), which should simplify printed circuit board layout. Routing is complicated when all the connectors are on one end of the board, as in the AT. By now you've probably figured out which bus is my favorite. :-)