-XX:+UseCompressedOops JVM command-line option is one of the most talked-about options of 64 bit JVM. Though 64 bit JVM allows you to specify larger Java heap sizes it comes with a performance penalty by using 64 bit OOPS. Ordinary object pointers also are known as OOPS which is used to represent Java objects in Virtual Machine have an increased width of 64 bit than smaller 32 bit from earlier 32 bit JVM. because of the increased size of OOPS, fewer OOPS can be stored in CPU cache registers which effectively reduced CPU cache efficiency. -XX:+UseCompressedOops enables the use of compressed 32 bit OOPS in 64 bit JVM which effectively compensates the performance penalty imposed by 64 bit JVM without scarifying heap size advantage offered by them.