an OS question

[cellio]

While waiting for assorted software updates to install today I found myself wondering... Mac OS and Windows usually need to reboot your machine to install updates. Yet I have, several times, seen Unix machines that I believe were being maintained with uptimes of more than a year. What's the deal? Is Unix just better able to support hot-fixes, or are Unix updates that rare? (Or am I wrong about the maintenance of those machines?) And if it's that Unix is better at updating, why does Mac OS, which is Unix-based, need to reboot so often? Mind, it's definitely better in this regard than when I was running Windows; this is a puzzle, not a rant.

Edit: Thanks for the comments thus far. I now understand more about how Unix is put together, and why Windows is different. Still not sure about Mac OS but comments suggest it could be UI-related (that is, the GUI might be more tied into the OS than is the case on Unix).

Comments

[sethg]

I don’t know about Mac OS, but aside from what others have said above, there is a specific difference between Windows and Unix-family filesytems that is relevant here.

In Unix filesystems, there is a level of indirection between a file’s name and its inode, which contains things like the ownership, permissions, and pointers to the blocks storing the actual data on the disk. Because of this indirection, one process can open a file, another process can delete it, and the storage the file uses will not actually be freed up until the first process closes it.

In Windows, back in the day, such was not the case: if one process had a file open another could not delete it. (I am using the past tense here because I just tried doing that with Windows 7 and I succeeded. Maybe NTFS has finally caught up with the 1970s, or maybe the user interface just removes the icon from the desktop without actually deleting anything.) So if an upgrade had to modify some file that the OS needed to keep open, then the only way to accomplish the upgrade was to shut down the computer and swap in the new versions before the OS reopened them.

[cellio]

Oh! I hadn't made the connection about inodes, even though (1) I know what they are and (2) I've been frustrated by that complaint from Windows that some (unnamed, mysterious) process is using a file I want to delete. Yeah, that makes sense!

I'm currently on XP at work, though I understand that Windows 7 will be rolling out next year. I should be good until October, when the lease on my current machine expires, assuming nothing melts down that would require earlier replacement. (My goal is to be among the last to get it, not among the first. That's not specific to Windows 7; for any expensive transition, I want to be able to benefit from what others have learned, 'cause my deadlines aren't going to get pushed out just because I now have to figure out accessibility, security, and just plain usability in a new environment.)