A memory block is considered as dead if the process which created the block exits (no longer around). Each block keeps track of the address and pid of the process which created it. During periodic memory tallying, if the process that scheduler finds out from a block pid doesn't match the the process that the block remembered, the block is marked as dead. The "dead memory" in IOS is misleading as not all of the "dead memory" may actually be dead, and might still be in active use by the system. In IOS it is relatively common for one process to allocate blocks that will stick around even after that process is dead. This is especially true for configuration processes like exec which might create all sorts of things. So memory marked as belonging to process *Dead* was allocated under the control of a process that is no longer running. It is normal to have a significant chunk of memory in such a state--for instance, if persistent system data structures are created due to the actions of some process, the memory will be marked as belonging to that process, but the process doesn't ever return the memory (some other process may return it later on). The only way to actually clear that is to reload the device.