After RAM upgrade on 32-bit Oracle server, ORA-04031: unable to allocate x bytes of shared memory

We are in the process of upgrading our Oracle database server at work, from SUSE Linux Enterprise Server 10.4 / Oracle 10g / 4GB RAM (Intel 32-bit) to Scientific Linux 6.4 / Oracle 12c / 8GB RAM (Intel 64-bit). As the first step, the additional RAM has been installed, but due to some application-related issue we had to pend the rest of the planned upgrade. ***To clarify**, the server is still running Oracle 10g and SLES 10.4. No change has been made on the software side* Since the installation of the additional RAM, however, the only database instance on that machine has been running out of shared memory (with the error in the title) two afternoons in a row. The depletion was severe enough that the only way to recover was using `SHUTDOWN ABORT`. No configuration change has been made, e.g. to the memory settings of the database: NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ lock_sga boolean FALSE pre_page_sga boolean FALSE sga_max_size big integer 1632M sga_target big integer 1632M pga_aggregate_target big integer 384M db_16k_cache_size big integer 0 db_2k_cache_size big integer 0 db_32k_cache_size big integer 0 db_4k_cache_size big integer 0 db_8k_cache_size big integer 0 db_cache_advice string ON db_cache_size big integer 960M It seems that the extra RAM actually cause the Oracle database software to have less RAM available to itself than before, but how exactly is this happening?