1. Location: The computer memory is placed in three different locations.

2. CPU: It is in the form of CPU registers and its internal cache memory (16K bytes in case of Pentium)

3. Internal: It is the main memory of the system which CPU can access directly.

4. External: It is in the form of secondary storage devices such as magnetic disk, tapes, etc. The CPU accesses this memory with the help of I/O controllers.

5. Capacity: It is expressed using two terms: Word size and number of words.

6. Word size: It is expressed in bytes (8 bits). The common word sizes are 8, 16 and 32 bits.

7. Number of words: This term specifies the number of words available in the particular memory device. For example, if memory capacity is 4K x 8, then its word size is 8 and number of words are 4K = 4096.

8. Unit of Transfer: It is the maximum number of bits that can be read or written into the memory at a time.

9. Access methods: A fundamental characteristics of a memory is the order or sequence in which information can be accessed.

10. Random Access: If storage location can be accessed in any order and access time is independent of the location being accessed, the access method is known as random access.

11. Serial access: If storage locations can be accessed only in a certain predefined sequence, the access method is known as serial access.

12. Performance: The performance of the memory system is determined using three parameters: access time, memory cycle time and transfer rate.

13. Access time: In case of random access memory, it is the time taken by memory to complete read/write operation from the instant that an address is sent to the memory.

14. Memory cycle time: This term is used only in concern with random access memory and it is defined as access time plus additional time required before a second access can commence.

15. Transfer rate: It is defined as the rate at which data can be transferred into or out of a memory unit.

16. Physical time: The two most common physical types today are semiconductor memory and magnetic surface memory.