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Comment by konstruktor | Hacker News Reader

I think inplicitly Kay is talking about personal computing, not servers, and that in isolation is a very narrow perspective. But following his thinking for a moment: does a 'PC' need VMs, ZFS and dtrace? Apple has shown that, by removing many things that seemed essential, like a user-visible file system, you can build a personal computer that appeals to a lot of people. I firmly believe this is not the right tradeoff to make, even for personal computing in general, but people are throwing loads of money at them...

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If you are talking about iOS... it still has the concept of a filesystem [1], albeit in a slightly different form than normal.

Even if Alan Kay is talking about PCs and not servers, you still need important things like the ability to connect to the Internet (TCP/IP), IPC, VMM, threading and multi-tasking, etc. I suspect I've not understood your point though, so feel free to clarify what I've missed :-)

1. http://developer.apple.com/library/mac/#documentation/FileMa...

2. https://developer.apple.com/library/mac/#documentation/perfo...

When I started using Unix in the mid-90s, RAM was still expensive, and the rule thumb was that to get best use of a workstation you should have 2x main memory as swap, 4x for a server. This was reckoned to give the best trade-off between the number of processes running and the working set you actually needed.

Shortly afterwards this stopped making sense because RAM got cheap. Should a 4G PC have a 16G swapfile? Should a 256G server have a 1T swapfile?

In short virtual memory was a hack to get around economical constraints. If you have the main memory, use it! Were it not baked into the OS at a deep level, I've have stopped using swap 10 years ago. It could be taken out of the next version of all the main OSs altogether, and no-one would even notice.

I didn't actually mean to add that second link in there (I realised you were talking about virtual machines and edited my comment accordingly... But forgot to remove the second URL!)

However, disk-backed page faults are but one component of a virtual memory subsystem. The real genius is the OS can provide access to memory uniformly in a way that is transparent to processes.

Indeed but in practice, paging to disk and memory protection are so entwined now.

Not really. In Windows its just a change to a system setting to disable the swap file, and in a unix it's a config file change or a command like swapoff to turn it off.

The fact that the two are entwined now is because of system defaults and decisions by OS developers on how to implement the page replacement algorithms in MM subsystems.

swapoff -a

Bitter experience has taught me to have a swapfile 1x main memory and set swappiness=0 in the kernel.

Apple doesn't "remove a user visible file system", they just make direct file system manipulation not as much of a necessity. And yet, this is not why their OS is good: it's because, if you want to, you can manipulate the file system and view it in as much detail as a BSD (OpenBSD) server, with just as much ease, combined with great hardware-software compatibility.

I think konstruktor was talking about iOS.

The system still has the complete filesystem implementation, and despite it not being visible to end users I imagine life would be much harder for developers without it, at least without replacing it with something likely to actually be even more complex (in code, not in UI). I mean, it isn't like VM or DTrace is "user-visible"; if anything, it is less user-visible/intrusive than its predecessors.

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