13. Computer data storage. What do terms memory, storage, primary storage, secondary storage refer to?

Computer data storage, often called storage or memory, refers to computer components, devices, and recording media that retain digital data used for computing for some interval of time. It provides one of the core functions of the modern computer, that of information retention.

Memory usually refers to a form of semiconductor storage known as random access memory (RAM) and sometimes other forms of fast but temporary storage. Storage more commonly refers to mass storage - optical discs, forms of magnetic storage like hard disks, and other types slower than RAM, but of a more permanent nature. Primary storage is the only one directly accessible to the CPU which continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner.

The specific functions of internal storage are to hold (store): all data to be processed; intermediate results of processing; final results of processing; all the instructions required for ongoing process. Another name for primary storage is memory, because of its similarity to a function of the human brain.

Secondary storage, or storage is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile.

14. The most commonly used storage technologies: semiconductor, magnetic and optical. Their performance characteristics.

The most commonly used storage technologies are semiconductor, magnetic, and optical.

The most important performance characteristics of a storage unit are:

 Speed, measured in cycle time.

 Capacity, measured by the number of machine words or binary digits.

 Reliability, measured by the number of failures per unit of time.

Semiconductor memory uses semiconductor-based integrated circuits to store information. In modern computers, primary storage almost exclusively consists of dynamic volatile semiconductor memory or dynamic random access memory. Since the turn of the century, a type of non-volatile semiconductor memory known as flash memory has steadily gained share as off-line storage for home computers. Removable flash memory is solid-state, rewritable memory; it is non-volatile, so it retains data when the power is turned off. This explains its popularity in small devices.

Flash memory cards are found in cameras, PDAs and music players. Flash drives, also known as thumb or pen drives, are connected to a USB port of the computer. They let you save and transfer data easily. Magnetic storage uses different patterns of magnetization on a magnetically coated surface to store information. It is non-volatile. The information is accessed using one or more read/write heads which may contain one or more recording transducers. A disk drive spins the disk at high speed and reads its data or writes new data onto it. Magnetic storage takes these forms:

 Floppy disk,

 Hard disk,

 A portable hard drive is an external unit with the drive mechanism and the media all in one sealed case. You can use it to make a backup, a spare copy of your files, or to transport data between computers.

 Magnetic tape data storage, used for tertiary and off-line storage.