noah@Apple.COM (Noah Price) (08/12/90)
In article <43739@apple.Apple.COM> austing@Apple.COM (Glenn L. Austin) writes: >>In article <43487@apple.Apple.COM> somebody wrote: >>Regarding the ci, doesn't the way memory is allocated affect certain >>games? >As long as the games use the Memory Manager, there should be no problems. The >only problems show up when you have smaller SIMMs (in RAM size) in bank A than >you do in bank B. If you have the larger SIMMs in bank A, the memory map is >the same as it is on any other II-class machine. This is probably one of the most mis-understood "problems" on the IIci. In brief, to programs executing on the 68030 (i.e., normal programs, not NuBus master cards, etc.) memory appears exactly the same on a IIci as on previous Mac II's, *except* that it does not "wrap." On previous Mac II's, if you had four meg of memory, it would repeat to fill the address space. Thus, if a program makes an access where there is no memory, it would access a "wrapped" location. On the IIci, it recognizes that there is really nothing there, and causes an error. The problem Glenn alludes to is only an issue for NuBus masters, that is, cards on NuBus that write directly to main memory. (however, it doesn't matter which bank has more memory, only that you have memory in both banks two banks and/or use the built in video.) Most cards are slaves; they get read and written by the processor, but never do any reading or writing them selves. Masters, on the other hand, can read an write memory themselves. Since they can't access the MMU on the 68030 (which translates the physical addresses to logical addresses seen by the programs) they see physical addresses. Unlike previous Mac II's, the IIci leaves a hole in the physical address space between the two banks. In addition, if you are using the built-in video, a block of memory from the bottom of Bank A is used for the frame buffer. This is getting a bit techie -- if you have questions or want a more complete explanation, plz e-mail or direct followups to comp.sys.mac.hardware. noah ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ noah@apple.com Macintosh Hardware Design ...!{sun,decwrl}!apple!noah (not the opinions of) Apple Computer, Inc.