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Understanding OS X Kernel Internals
jglidell writes "The OS X kernel has been in the news alot this past year, whether it's why its slow, Mach/micro-kernel makes it bad, it's going closed source and what not. Amit Singh has put up a new presentation on the innards of OS X. It does a pretty good job of summing up the OS X kernel architecture, and has some pretty detailed diagrams... for instance they show that there are so many process/threads layers in OS X. So if you are in the mood for doing some OS studying then head over."
I have a small program that mmaps a bit of code and then points the program counter at it. Everything runs fun until a OS call happens. I've heard that Mach allows user land programs to install their own OS calls but I haven't seen any example code to do it and I suspect such a feature isn't in OS X. I've hunted through the source and I while I could write my own system call and compile it in, there should be an easier way. Can anyone point me in the correct direction?
I think much of OS X's ram-hungriness comes from the fact that outside of the system frameworks, there is very little utilization of shared libraries among the different applications. Each app bundle is largely self-contained with its own shared libraries. Granted most apps that ship with OS X (from apple) just access the shared frameworks in /Library/Frameworks and have few other dependencies in their bundles. But start adding apps like MS Word, Firefox, OpenOffice, etc, and you'll start having multiple copies of various libraries loaded. The app bundle system is very simple and reliable, but because of the shared library issue, you'll always need more ram when running these apps on OS X than Windows or Linux.
Definitely 1 GB is a minimum amount of RAM needed for OS X Tiger these days. That is quite sad when you think about it, but RAM is cheap so I'm not too concerned about it. Apple has always shipped their machines short on RAM, hoping you'll pay ridiciulous amounts of money for their official RAM upgrades.
As an ex-NeXT developer, the historical speed bumps behind this architecture are directly related to code density. NeXTSEP ver 2.0 was nicely running on 25mHz. NeXTSTEP ver 3.0 suffered performance on 25mHz compared to ver 2.0 because of the additional kernel overhead resultant from code densification.
With every ver. release through 10.4.x MacOS X, mach/BSD layer exhibits funtional improvements with speed increases of the processor CPU and latent performance behaviors from the additional kernal overhead added by code complexity and densification.
Prima Facia evidence to the 4X speed improvement in performance from Apple's new Intel CPU bears witness to the limits of the kernal architecture.
You're assuming that the only market for software is medium to large enterprise. Autocad (which is made by a well known vendor) is used by tons and tons of architects. Since I've worked in IT support for a few architectural firms, I can tell you that most of them are comprised of small business of under 50 employees. I've used Autocad under Windows, however when I needed to use something to make some plans for a shed for my church, I used Sketch-Up, because there's an OSX native version.
Furthermore, most of the people that I've run across who are excited about virtualization are primarily interested in using it to run the existing Windows apps they own, and plan on replacing those with OSX native versions where available, and comparable OSX native apps where not available. The other major segment (where I fall into this equation)interested in virtualization, is the IT people who use/support multiple platforms.
Boot Camp is for games. Noone I have spoken with that knows about virtualization is seriously intersted in using it for anything other than games.
What?
I'm not understanding something...
This seems like Carly Fiorina Logic. If we stop making HP calculators, people will just buy handheld HP units with similar funtionality. It doesn't matter that the calculator group provides a substantial net profit for the company. If we stop spending all that money on supporting calculators and simply use the computer support people we already have... Think of the savings!!!!
When a group/division in a company that caters to a market makes the company lots of money, leave them alone. They're doing their job, pulling a PHB stunt in wall street business tactics will only hurt your company.