Shared memory

Shared memory refers to a (typically) large block of Random access memory that can be accessed by several different central processing units (CPUs) in a multiple-processor computer system. The problem with shared memory systems is that the many CPUs need fast access to memory and will likely cache memory. Whenever one cache is updated with information that may be used by other processors, it needs to immediately update the shared memory, otherwise the different processors will be working with different data.

The alternative to shared memory is distributed memory. This has its own issues.