Types of Computer Memory and their Management

In computing memory refer to a device which is used to store a information for immediate used in a computer.
A computer memory is divided into two broad categories which is known as
primary memory
secondary memory

Primary memory:- 

                            primary memory is a internal memory of a computer. It contained on a computer chips and used a electronic circuits to store information. In primary memory, data is not stored permanently, the data is lost when the computer is turn off. The access speed of a internal memory is very high as compared to secondary memory because it accessed directly by the central processing unit.
There are different type of a primary memory are
Read Only Memory (ROM)
Flash Memory
Random Access Memory (RAM)

Read Only Memory:-

                          In Read Only Memory instructions are stored permanently, the store data is not removed when the computer is turn off. Read Only Memory is a Non-volatile Memory. ROM contain a instructions that is very important for computer to start up (boots up). The instructions are read before software program load in the computer from a small program in the ROM. The small program or small part of a ROM is called a "BIOS". Read Only Memory is not re writable it allow only reading. Read Only Memory contain data when computer is switched off.

Flash Memory:-

                       Flash Memory is a solid, Non-volatile and re writable memory. The Flash Memory is used in digital camera's, cell phones, printers,Audio recorders and hand held computers because the speed of Flash Memory is high and the Flash Memory used a low voltage.

Random Access  Memory:-

                                        Random Access Memory is a storage device that can be accessed randomly at any time in any order and from any location. Random Access Memory is a volatile memory. what is volatile memory????
In volatile memory the stored data is lost when computer is off and data remain in memory when machine or computer is running.
Random Access Memory is a readable and re writable memory. We can read data from memory at any time and we can delete the data at any time and again we write data in the memory.
There are two types of Random Access Memory
Static Random Access Memory
Dynamic Access Memory

Static Random Access Memory:-

                                                   Static RAM is a volatile memory it never needs to be refreshed the stored information as power is applied. The content of memory is lost when power is turn off.

Dynamic Random Access Memory:-

                                                         Dynamic RAM is a volatile memory it needs to refreshed the stored information periodically otherwise stored information would be vanish.

Secondary Memory:-

                                 secondary memory is slower than primary memory. Secondary memory is not directly connected to the computer. It hold data after the computer is turn off. Secondary memory has a large capacity to store information but the Access speed of memory is slow. Secondary memory use a inexpensive mass-storage device so secondary memory is inexpensive.
Types of Secondary Memories are
Magnetic Storage Media
Optical Storage Device
Magnetic Storage Device:-

Management of computer memory:-

               The management of computer memory is very important to operate correctly otherwise it leads to bugs, slow performance and virus in the computer.
Arithmetic overflow, segmentation fault, memory leak are all problem of improper management of memory.
Virtual memory and Protected Memory is used to properly manage the computer memory.

Virtual Memory:-

                          When a program needs a memory it request to operating system then operating system decide the location of physical memory to place the memory.
The benefit of virtual memory is where the memory is stored physically without the worry of computer space.

Protected Memory:-

                              In protected memory particular range of memory is allocated to each program to run properly. When program tried to used the space of other program then system terminate the program and help to save data to used incorrectly. protected memory is used to enhanced the reliability and security of the computer system.
       

Disk Storage

         The data (record) is stored in a database system. The database system uses several types of memory to stored data in a database system. Three types of memory are most common. Disk storage, magnetic tape, main memory are a major type of memory but optical disk and other devices are also play a vital role in database system. The brief description of disks storage is here to explain the characteristics of disk storage.

                 Disk storage is nonvolatile it means that the data is not erased when system is shut off. The portion of a data can be accessed in any order so disk is a direct access storage device (DASD).  The disk is available in 3 ½, 5 ¼, 8 or 14 inches. The composition of magnetic disks is a circular metal (plastic platters) coated with a film of magnetized material. Disk drives are used to stored and read a data from a disk. 

How disk work to store data?? Data is stored by tracks on the surface of the disk. In movable-head disk unit read/write head is attached to an access arm (access arm is a rod that can be moved on the surface). Disk is rotated when read/write head is position over a track then the entire track is passes under the read/write head. The data can be stored and read at any position because of the arm movement and disk rotation. In fixed-head units for every track there is a read/write head.

Dust and smoke particle cause a major problem when read/write head were moved closer to the tracks. But now Sealed the disk and read/write head in a dust proof housing the Winchester technology reduces dust and smoke contamination problem. What is a Winchester technology??? Who Winchester technology reduces dust and smoke problem?? Winchester cartridges consist of high-capacity rigid disk in sealed housing and Winchester drives are high capacity unit that hold portable or permanently mounted sealed disks. 

The set of tracks that are in the corresponding positions on their surfaces is called a cylinder. The number of cylinders in a disk pack is obviously the same as the number of tracks on each surface.

The time to transfer data from disk to main memory is determine by the following

Seek time:  the time that read/write head takes to reach the correct track. The seek time is shorter when the desire position is near to the head current position.

Rotational delay time/latency time: the time it takes to rotate the disk

Head switching time: the time to select the correct read/write head for the surface needed.

Transfer time: the time to move data from the disk to main memory.

The factors that are important for determining the capacity of the disk are

Composition of the disk, it’s size, data density, number of the bits stored per inch of the track, and number of track per inch surface.

Hard disks rotate faster than floppy disks, hard disks rotate in the range up to about 4700 revolutions per minute and floppy disks rotate in the range of 300 to 600 revolutions per minute.

The mechanical movement in using disks cause a crushed of head, the disk unit fail and destroy a data cause a major problem. Fixed-head disk unit may be used when time is crucial because the spinning of disks and the movement of access arms caused delays of data access.