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I've never used Multics myself, but from what I understand it was also based on the idea of mapping files in memory. When I first heard this, I thought the idea was pretty neat, but then the person I was speaking to remarked that it wasn't all that great in practice. I'm not really sure why, but I'm curious.

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`mmap()` sucks if you don't have a lot of addresses. 64-bit computers now have a lot of addresses.

I'm skeptical this was the reason, though (at least in and of itself). Going off of https://en.wikipedia.org/wiki/Multics#Novel_ideas, it seems that the address space (36 address bits ⇒ 36 bits/word × 2³⁶ ÷ 8 bits/byte = 288 GiB) was much larger than memory of the machine Multics was designed for (about 2 MB), and the size of a segment was limited to about 1 MB (36 bits/word × 2¹⁸ ÷ 8 bits/byte), nearly half of all memory – so I doubt this was troublesome at the time.

because now you've turned failed IO operations from an errno into a segfault.

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