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  The range of memory and storage devices within the computer system. The following list starts with the slowest devices and ends with the fastest. See storage and memory.

      VERY SLOW

   Punch cards (obsolete)

   Punched paper tape (obsolete)

      FASTER

   Bubble memory

   Floppy disks

      MUCH FASTER

   Magnetic tape

   Optical discs (CD-ROM, DVD-ROM, MO, etc.)

   Magnetic disks with movable heads

   Magnetic disks with fixed heads (obsolete)

   Low-speed bulk memory

      FASTEST

   Flash memory

   Main memory

   Cache memory

   Microcode

   Registers

• Coherency – In computing, cache coherence (also cache coherency) refers to the integrity of data stored in local caches of a shared resource. Cache coherence is a special case of memory coherence.
  When clients in a system maintain caches of a common memory resource, problems may arise with inconsistent data. This is particularly true of CPUs in a multiprocessing system. Referring to the "Multiple Caches of Shared Resource" figure, if the top client has a copy of a memory block from a previous read and the bottom client changes that memory block, the top client could be left with an invalid cache of memory without any notification of the change. Cache coherence is intended to manage such conflicts and maintain consistency between cache and memory.

• Consistency - In computer science, in a distributed system such as a distributed shared memory system or a distributed data store such as a database, filesystem, web caching or optimistic replication systems, there are a number of possible data consistency models. The system supports a given model if operations on memory follow specific rules. The data consistency model specifies a contract between programmer and system, wherein the system guarantees that if the programmer follows the rules, memory will be consistent and the results of memory operations will be predictable.