Re: Explaining single level store to non i people

[Joe Pluta <joepluta@xxxxxxxxxxxxxxxxx>]

Hans Boldt wrote:
> Joe wrote:
>   
> > The essential goodness of SLS is that no part of the application is
> > ever involved with moving things between memory and disk. Everything
> > has an address, and when you access that address, the operating
> > system decides whether data is available or whether it needs to be
> > paged in.
> >     
>
> On the other hand, the internals of single-level store are rarely exposed
> to the iSeries programmer. Within a program, you still deal with a model
> where you open, read, write, update, and close files. That is, the
> programmer deals with a model not unlike that of conventional systems.
>
> Actually, you can't really have it any other way. One way or another, the
> operating system still needs to synchronize access to the "file" objects.
>
>   
Your objection really has nothing to do with my statement.

I'll try to make it a little clearer.

In a traditional system, you have multiple places where things get read 
into and out of memory.  One example  is reading data from a file, which 
is relatively trivial (at least when reading from something like a disk 
drive).  Another example is reading a program in; that requires a 
different sort of read as well as some cool address translation as you 
move it from disk to physical memory.  These two things are very 
different in non-SLS systems, but they're virtually identical in SLS, 
because in both cases as far as the application level and supporting 
routines are concerned, it's just a memory access.

If you don't understand the different between that and the fundamental 
differences in, say, a Unix or Windows environment between loading a 
program and reading a disk file, then I guess I'm unable to get my point 
across.  Similarly with the JVM issue.  JVMs don't page.  If you're not 
convinced, run Java on any memory starved system (*nix, DOS, i5/OS) and 
watch the thrashing.

This is just common sense stuff.  If you don't see it, that's cool.

Joe