Every block of storage on an a System i disk drive has a virtual address for
that block of storage stored in it. Every time you create an object, it
allocates 16mb of virtual storage to it (Not physical storage) so the first
block of physical storage would have the starting virtual address for that
4096 byte block. I assume that the System i maintains a cross reference
table that says this virtual address is this physical block of storage.
There is one MI instruction that resolves to everything in the system RSLOBJ
(Resolve Object I think I got that right) that returns a virtual address.

On Thu, Aug 13, 2009 at 3:15 PM, Walden H. Leverich <WaldenL@xxxxxxxxxxxxxxx

Sure. In SLS you can simply think of the machine as storing everything
in memory. There is no "filesystem" as we'd think of it on a windows or
linux machine. You're programs simply refer to memory locations and they
get data. This is best seen in either the System Entry Point Table
(SEPT) which stores "memory addresses" for well known system programs so
they don't have to be resolved, or in a logical file. The entries in the
logical store the memory address of the related row in the physical.
This makes accessing anything extremely simple, get its address and go
there. The guts that make SLS work will then determine if that address
is actually in physical memory, or if it needs to fault it into physical
memory, but that's a process that occurs _way_ down in the plumbing.

What I mean by "memory survives a reboot" is that these addresses that
SLS exposes to everything above it don't change across reboots (IPLs).
Sure, the actual stuff in the RAM chips on the cards was tossed, but
those are just cache in essence, the address that held the QCMD program
object on IPL 1 will still hold the QCMD program object on IPL 100. The
"address" of that object doesn't change. If you're thinking of SLS as
one big hunk of memory then the memory survives a reboot.

At least this is how I understand SLS -- My name's not Frank Soltis. :-)


Walden H Leverich III
Tech Software
(516) 627-3800 x3051

Quiquid latine dictum sit altum viditur.
(Whatever is said in Latin seems profound.)
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