What is it <sid>CORE.LOG trace file?

Hi,

can somone help me, please? Does anybody knows when and what is stored in <sid>CORE.LOG trace file in %ORACLE_HOME%/RDBMS73/TRACE directory? Sometimes, it is generated during some queries, but sometimes not! Moreover, when this file is generated, client's session is terminated on server (I can't see it in v$sessions), but client still 'thinks' that session is active (seems, tah query is still running). After the crash has happened, query can't be executed, even I kill my client application and reconnect to server. Later (say, on next day), my query is executed again!

Seems a little bit strange, doesn't it?

Sincerely,
I.Grinbergs

P.S. Here is a short quote from beggining of trace file:

Oracle7 Server Release 7.3.3.0.0 - Production Release Process Id: 0x00000091 Thread Id : 0x00000032 Time : Wed Dec 03 16:38:49
Excp. Code: 0xc0000005 Excp. Type: ACCESS_VIO Flags: 0x00000000

• Memory Map of process ---------------- Start Addr-End Addr Type Size ModuleName 0x00240000-0x0026efff Image 0000192512 d:\orant\bin\CORE35.dll 0x00270000-0x002b9fff Image 0000303104 d:\orant\bin\NLSRTL32.dll 0x002c0000-0x002e5fff Image 0000155648 d:\orant\bin\CORE35O.dll 0x002f0000-0x003bffff Image 0000851968 d:\orant\bin\PLSK233.dll ...