Dynamic memory is RAM plus swap files on the hard disk.
Most Unix operating systems have per-process limits dynamic memory, which can be adjusted by the system administrator. These OS settings limit the amount of dynamic memory that the OS will allocate to any individual process, such as an S-PLUS session. In this example, the error message says that the operating system had already granted earlier S-PLUS requests for a total of about 989.35 megabytes of dynamic memory. It doesn't update the destination object until it is sure that the new answer is available and correct. While it is processing and verifying, it creates temporary copies, which take up memory until the destination object is updated.