RE: How much memory do you REALLY have?

Joe (et al):

There are 3 different answers to "How much memory . .".  It depends upon 
whether you are on:

iSeries hardware without partitioning
iSeries hardware with partitioning
i5 hardware (with or without an HMC).

On iSeries, the only memory you "lose" (you actually are using it, it just 
is not available for your partition memory pools as shown on WRKSYSSTS or 
WRKSHRPOOL) is taken by the hardware page table.  That's why, on a 
partitioned iSeries, the primary partition's minimum memory is usually 
required to be significantly higher than a secondary partition.  There is 
a formula for the size of this table but it's there somewhere in "The 
Information Center".

On i5 hardware, there is memory used by the Service Processor.  This is 
for the processor itself plus the tables that control partitioning and, of 
course, the hardware page table.  If you have an HMC, it is possible to 
find out where it all is.  There is a metric called "firmware memory" 
which gets allocated before a new partition (or the only partition) is 
activated.  For example, on my little 520 with 2GB total memory and 3 
partitions, I have:

Partition 1     1,248
Partition 2        320
Partition 4        256
Firmware         224
----------------------------
(total)           2,048
     (Note - memory granularity, the smallest increment that can be 
assigned, is 16 MB on this machine.  Your mileage may vary.)

The bad news is that, using the HMC's standard GUI display, you cannot 
determine the "firmware memory".  Nor with WebSM.  You have to use the 
command line access through SSH.  You could, of course do the arithmetic 
and, essentially, do "sales by disappearance" logic.  IBM may repair this 
deficiency someday.

Dave Schnee,
Barsa Consulting Group, LLC

Joe Pluta wrote:
> In the meantime, I'm asking people to check their machines.  Go
> into WRKSHRPOOL and see if the amount reported matches what you
> bought.  I'll be interested to see what the results are.