Rockwell Automation 1757-SWKIT4000 ProcessLogix R400.0 Installation and Upgrade Guide - Manual (Page 220)

Publication 1757-IN040B-EN-P - March 2002
9-12 PC Performance for ProcessLogix Systems
Windows 2000, have the ability to take memory space occupied by
data in physical RAM and swap it into a file. This frees up the physical
RAM for other processes.
If the process again requires the data that was swapped out, a page
fault occurs and the page is swapped back from the file into physical
RAM before operation continues. This type of management is called
Paging and the associated swapfile is called the page file.
In Windows 2000 using Task Manager, looking at the Total Limit in the
Commit Charge section of the Performance tab, the Total value is the
amount of Physical RAM and Swapfile combined. The Physical
Memory section shows how much of the Physical memory is available
for use.
Page file settings include a lower and upper limit. The lower limit is
typically the amount of physical RAM plus management space. This is
almost always 1.5 times the amount of physical RAM. The system
typically suggests that the upper limit be set to around 3 times the
amount of physical RAM.
Windows 2000, in normal operation, only uses the lower limit size.
The value of the lower limit (Initial Size) is pre-allocated. If the usage
exceeds this limit, the system will then continue to allocate additional
space until the upper limit (Maximum Size) is reached or the system
runs out of disk space. If this occurs, it usually means that an
application/process is leaking memory.
Some paging of memory for systems is normal. Excessive paging will
hurt performance as there is a hit taken during the swapping and
allocation phases. Memory performance can be degraded during some
operations as long as they are not prolonged or part of normal system
operations. The goal is to produce perfectly balanced systems. Ones
which have enough physical RAM for normal operations and the
ability to Page when an abnormal event is required. Systems who
perform paging operations frequently during normal operations will
receive great performance benefits by adding more physical RAM.
Rockwell Automation attempts to specify default memory
configurations to minimize paging during normal operations of the
system. Scaled via Small, Medium, and Large Systems, and then
broken up by Operating System, you should use these tables as a
starting point. You should then monitor the Pagefile usage to
determine whether or not your system could benefit from added
physical RAM.
At any time memory is added or removed from the PC, the operating
system should be adjusted based on the system type described below.