How Does an Apple Macintosh Work?

[Doctor Q]

I've done surgery on the Windows registry more than once to fix installation problems, so I know what a mess it can cause.

But I'm still not convinced that a central repository of system information isn't sensible. In Mac OS 9 and earlier, the desktop database was a central repository of application information. It made the Finder efficient. Maybe its nicest feature was that, when the desktop database was trashed, you could simply rebuild it.

Even directories under /Library are central repositories. They just happen to contain separate files, many of them XML files, rather than a single system-maintained binary version of the same information. Either way, it's a huge tree-structured set of keys and values and any application has permission from the operating system to write to the files there.

What I'm starting to believe is that the Finder's desktop database taught us a lesson. Have each application keeps its information in a private place, and have the operating system collect a cache with the same information, as opposed to letting each application update the central files directly. That way, the operating system has everything it needs in one place (good performance), the O.S. has the only code that writes to the repository (safe from application bugs) and you can rebuild when necessary (a way out when things go wrong).

 

[ColdZero]

Re: obligitory answer

Originally posted by slowtreme
How does it work... Pixie Dust

No, Pixie Dust is how IBM got higher densities on their hard drives. And I'm not joking either, it was called Pixie dust. Thats why I laugh every time I see the commercial for IBM where the have the "magic server pixie dust"

 

[Makosuke]

Re: Re: obligitory answer

Originally posted by ColdZero
No, Pixie Dust is how IBM got higher densities on their hard drives. And I'm not joking either, it was called Pixie dust. Thats why I laugh every time I see the commercial for IBM where the have the "magic server pixie dust"

Shoot! You beat me to that one.

(Official IBM Link)

I agree that I understand the curiosity behind things like this; it's the same thing I do when I start messing with a new platform or technology (say, the BeOS)--how does it do what it does? For that matter, why did the architects make those decisions?

I prefer the Developer version of the Architecture document linked earlier, since it goes into more detail if you're willing to spend the time reading:

http://developer.apple.com/macosx/architecture/

and even better, the System Overview Book.

Whatever you think of the registry, you've got to love the ease of installation of most apps in OSX. Since all of the application's resources are contained in a simple folder (what apps really are), they're highly portable. Apps are designed to locate the user's preference file (located in their Library folder), so preferences are system-wide and mostly centralized but user-specific.

Specific library information and application bindings are handled by the OS on-the-fly whenever the user moves stuff, opens a folder with installed apps, or runs a new program (prebindings and the like), so you get the advantages of efficient caching that Dr. Q talked about, while not having to worry about updating a set of static links if the application happens to get moved, installed, or deleted.

Of course, badly designed applications (or the few that provide services to the whole OS, like Safari) can require an installer, but for the most part that's unnecessary and I tend to avoid apps that do.

That's a big part of why the "just works" equation happens, and it was really satisfying to see in action the last time a PC user on a Mac in my office (we do things the other way around--force PC people to use Macs at work) asked me:

"How do I uninstall this program?"

"Drag the icon to the trash. That's it."

"Wow. That's easy."

 

[Fender2112]

A simple take on the issue ...

I think ArsTechnica is a good site to get some info on various apsects about computers. Some of it can be a bit technical, but it has a lot of information in one site.

From what I can gather the fundimental difference is the in the chip design. Macs us the PowerPC which is a RISC based chip and Wintel's use x86 chips that are CISC based chips. This difference between RISC and CISC revolves around how many and what type of instructions are performed during each clock cycle. It's kind of like comparing a rotary engine (Mazda RX7) to a four-stroke engine. The end result is the same but the methods are different.

I read a book a few months ago titled "Codes" which explains the evolution of the microchip. I recommend it if you want to know what those 1's and 0's really do.

Another analogy I use sometimes is this: Windows is a GUI wrapped around a DOS foundation and OS X is a GUI wrapped around a UNIX foundation. Over the course of time UNIX has become a much more powerful, robust and stable core than DOS. I'm not sure what OS 9 (and earlier) are wrapped around, maybe a Hershey's Kiss.

I am just a construction worker with a passion for Macs. This is my simple take on a very complex topic.

 

[notjustjay]

Hey now, Fender.. you're not "just" anything. You know far more about computers than I know about construction... so more power to ya!

 

[Iconocat]

Addicting!

Having just come back to Macs after about 11 years, I found myself wondering how they work as well.. after a little bit of investigation (a lot of the places that have been mentioned on this thread) I've found my thirst for knowledge increasing! I have to admit from the time I was forced to start using PC's (1992) until I got my new mac, I lost interest in them pretty quickly. (Windows just KILLED the attraction for me.)

Now I can't get enough learning about macs!!! I find myself wondering how much more I can charge on my credit card to buy yet ANOTHER Mac book (between this and ITMS... ouch!)

"It just works" is such a fabulous way to sum it up but once you really start to dig deep into WHY it does.. you think "It just works.. and HOW!"

I just felt like sharing!