OLD-CISCO-CHASSIS-MIB::processorRam
But that MIB has been deprecated since IOS 12.0.
-- *****************************************************************
-- OLD-CISCO-CHASSIS-MIB.my: Cisco Chassis MIB file
--
--
-- May 1994, Jeffrey T. Johnson
--
-- Copyright (c) 1994-2008 by cisco Systems, Inc.
-- All rights reserved.
--
-- NOTE WELL
-- Starting with IOS 12.0, all objects defined in this mib have been
-- deprecated. They have been replaces with objects defined in the
-- ENTITY-MIB.my document. Management applications should no longer
-- be examining the objects defined in this document.
-- NOTE WELL
--
-- *****************************************************************
CISCO-ENTITY-EXT-MIB::ceExtProcessorRam
is where they moved it. (7 years later.)
From my 2851:
Cisco 2851 (revision 1.0) with 1032192K/16384K bytes of memory.
CISCO-ENTITY-EXT-MIB::ceExtProcessorRam.3 = Gauge32: 1073741824 bytes
OLD-CISCO-CHASSIS-MIB::processorRam.0 = INTEGER: 1056964608
The entity mib is processor + io memory (all physical ram), and the old chassis mib is showing just the processor memory (as the name suggests)
If the service-engine is configured, then physical memory is partitioned, and it may not be reflected in SNMP.