> There is one axis along which I concede that things have advanced > since Multics, which is away from monolithic kernels -
Whether that is an advance or a regression depends on your priorities. I see good arguments each way. > But the complete structing of the system around a segmented, > single-level memory system (at least, in terms of the environment the > user sees) is such a fantastic idea that I simply don't understand > why that hasn't become the standard. Well, what was the largest virtual memory space available on various machines? On the VAX, it was either one gig or two gig, depending on whether you count just P0 space or both P0 and P1. When you're mapping objects of uncertain size, that seems awfully constraining - and, depending on the page table architecture in use, it can cost a lot of RAM to get even that much; the VAX, for example, needs eight megs of RAM to map one gig of space, and that doesn't even account for any memory used to back any of that space. And, back in the heyday of the VAX, eight megs was a lot of RAM. Now that 64-bit address space is becoming common, eight megs of RAM is ignorably small, and multi-level page tables are common, this looks a lot less impossible. I've been tempted to build something of the source, but I never got to use real Multics, and I would probably have trouble shaking free of the POSIX mindset. I should dig up some 64-bit machines and try to find enough documentation to build OSes for them.... /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mo...@rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
