Computer data storage, often called storage or memory.

1. A PC's main memory is fast storage that is directly accessible by the CPU, and is used to store the currently executing program and immediately needed data.
2. Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data used for computing for some interval of time.
3.  It use semiconductor random access memory (RAM) of various kinds such as DRAM, SDRAM or SRAM as their primary storage. Which exact kind depends on cost/performance issues at any particular time.
4. Main memory is much faster than mass storage devices like hard disks or optical discs, but is usually volatile, meaning it does not retain its contents (instructions or data) in the absence of power,
5. Main memory is directly or indirectly connected to the central processing unit via a memory bus. It is actually two buses (not on the diagram): an address bus and a data bus
6. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage.
7. When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information.
8. Storage technologies at all levels of the storage hierarchy can be differentiated by evaluating certain core characteristics as well as measuring characteristics specific to a particular implementation
9. The accessing of pieces of information will be in a serial order, one after the other; therefore the time to access a particular piece of information depends upon which piece of information was last accessed.
10. The relevant unit of measurement is typically nanosecond for primary storage, millisecond for secondary storage, and second for tertiary storage.