Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!sdd.hp.com!think.com!mintaka!pogo.ai.mit.edu!dbert From: dbert@pogo.ai.mit.edu (Douglas Siebert) Newsgroups: comp.sys.mac.hardware Subject: Re: LC video vs. SI video... (really built-in video in general) Keywords: video built-in Message-ID: <1991Mar6.043604.9943@mintaka.lcs.mit.edu> Date: 6 Mar 91 04:36:04 GMT References: <1991Mar6.094536.125@otago.ac.nz> <1991Mar6.011546.19535@midway.uchicago.edu> Sender: daemon@mintaka.lcs.mit.edu (Lucifer Maleficius) Organization: The Internet Lines: 32 In article <1991Mar6.011546.19535@midway.uchicago.edu> jcav@ellis.uchicago.edu (john cavallino) writes: >There are three (3) built-in video methods employed by Apple in Mac models. > >1) The Mac IIci and IIsi: >The frame buffer ALWAYS starts at absolute address 0, which is the first >address in SIMM bank A. This is where the video contoller always looks. >Depending on the screen depth selected in the "Monitors" control panel, there >is a variable amount of RAM left unused in bank A. The MMU maps this >RAM, along with any RAM in bank B, so that it appears contiguous in virtual >space, starting at virtual address 0. It also remaps the frame buffer to >appear in the address space corresponding to a NuBus card. The reason some >memory is slow and some not slow is that sometimes the absolute address falls >in bank A, which suffers contention delays with the video controller. If the >absolute address falls in bank B, there is no contention and no delay. This >is also why it is best to put expansion RAM in bank B first. I was under the impression that you couldn't, for instance, put 256K SIMMS in bank A and 1M or 4M SIMMS in bank B. Is it different for these machines? Also, if you purhcased a separate video card for the si or ci which included on-board VRAM, would the contention problem then go away? This would probably not be worth it if you only intended to get an 8-bit card anyway, but if you got a 24-bit card (which the on-board video doesn't support, correct?) then you would have better video and faster execution, all for only a few hundred dollars. Then I would see no real reason to purchase a ci over an si unless the extra slots were really important to you. Comments? -- ________________________________________________________________________ Doug Siebert dbert@albert.ai.mit.edu MBA Student (2nd year) The University of Iowa