RE: Single level store & record blocking on update files (was RE:Where is IBM?)

On Wed, 23 Apr 2003, Dan wrote:

> On the AS/400, there is no record blocking for update files, period.  I
> fail to see why this is, especially in light of the AS/400's single
> level store.

I think there is some confusion here as to what single level store really
is.  Single level store is a memory management technique, not a file
management technique (Hans will correct me if I'm off the mark).  So
reading a file in blocks has nothing to do with single level store, since
that is the job of the filesystem.  Indeed, that is what other posters
have demonstrated is true by the posts on file creation parameters.
Blocking is done on every platform - single level store or not.

> > This is because all storage on the iSeries, whether it be main storage
> > (memory) or auxiliary storage (disk) is addressed as if it were ALL
> > residing in main storage.  This even goes back to the System/38 days.

This is better stated as "all storage on the iSeries, whether it be main
storage or auxiliary storage, has an address that can be used regardless."
It is clear that the AS/400 treats storage in memory different than that
which is on disk - otherwise it would not page.  Note that this does not
magically give the AS/400 some wonderful new capabilities.  In fact, the
application programmer will never know that s/he is on a single level
store system or not as memory management is done by the core of the OS,
not by any exposed API (there are some exceptions like mmap() and other
APIs, but these control what to do with the memory allocated to the
program, not the memory model itself).  When you read some datum on the
disk the system will page it into memory, just like a non-single level
store system.

What single level store does enable is that the maximum memory available
is the amount of RAM + the amount of disk.  Other systems are limited to
RAM + swap space.

James Rich