From: Sean Russell <ser@...>
Date: 2002-05-07T06:14:37+09:00
Subject: Re: Ruby vs. Java vs. Native trivia

Chris Ross wrote:

> The reason that this occurs is due to the following:
> 
>    o dynamic: when the application is loaded into memory there is a delay
>      on startup as the OS's dynamic linker loads all libraries that are
>      required by it.
> 
>    o static: only the executable is loaded into memory - the dynamic
>      linker doesn't have to do anything. muchos faster.
> 
> Dynamic is more flexible as upgrading the library doesn't require a
> recompile of apps that use it.

I've never understood this.  AmigaOS was heavily dependant on DLLs -- in 
fact, I don't think it was possible to build an app without linking to 
DLLs.  Not only did the apps come up very quickly, but they consumed almost 
no memory, since huge parts of the codebase were, well, shared.  I remember 
that, out of 4MB, just booting AmigaOS would consume about 2.5MB... but 
then you could run an amazing number of applications -- graphics editors, 
word processors, etc. -- within that 1.5MB of space.

In any case, I'm /mostly/ baffled by the amount of memory and the time that 
is required by more modern OSes.  I'm sure memory protection has something 
to do with it -- I'd guess that DLLs aren't shared across user space apps 
-- but I don't get into the internals of Linux much.  Still, it would seem 
to me that the basic theory is fairly straightforward:  you load system 
libraries in a shared, non-writeable space, and everybody just accesses 
them from there.  The first person who runs KDE gets a big load time, but 
beyond that, it's just allocating per-user data spaces.  You unload the 
library when it isn't used and gets swapped out of memory.

This sounds rather off topic, and not the domain of Ruby anyway, but this 
has been bugging me for a while.

--- SER