ORA-27001 on Database Startup

Database: 10gr1 10.1.0.5.0

OS: Windows 2003 sp1 standard edition

When trying to start the database after enable PAE getting below error

ORA-27001 on Database Startup

fact: Oracle Server - Enterprise Edition
fact: MS Windows Platform
symptom: Database startup fails
symptom: ORA-27100: shared memory realm already exists
symptom: DB_BLOCK_BUFFERS parameter is not set too high for the machine resources

cause: Operating system has a duplicate Oracle memory segment still in memory.

fix:

Stop and start the database service. If this does not help, then a re-boot of the server will flush the memory

Metalink Note: 208285.1

Ora-27100 even After Restarting the Windows Service
Metalink Note: 370469.1

Changes

The parameter sga_max_size was changed from 2GB to 3GB through OEM Or Command prompt

Cause
Changing the parameter from OEM will make the change in the spfile.
ORA-27100 is received as a result of changes made to parameters affecting the SGA size.The service was created to start with spfile .When the service is restarted , it will use the spfile and the error occurs due to SGA parameter change.

Solution: try to start db with pfile instead of SPFILE.

How to enable PAE on windows platform

1. open boot.ini file (it is hidden system file)

2. add '/PAE /3GB' in the following format

[boot loader]timeout=30default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS[operating systems]multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows Server 2003, Standard" /noexecute=optout /fastdetect /PAE /3GB

3. restart WINDOWS machine

4. check the system properties for PAE addition confirmation as above picture.