Memory Units

Memory is a part of the computer that holds data for processing, instructions for processing the data and information (processed data). Memory may store data temporarily or permanently depending on the types of data and the storage device. There are two kinds of computers memory:- Primary memory and secondary memory.

  
Primary Memory:
Primary memory is accessible directly by the processing unit. RAM is an example of primary memory. As soon as the computer is switched off the contents of the primary memory is lost. You can store and retrieve data much faster with primary memory compared to secondary memory. Primary memory is more expensive than secondary memory. Because of this the size of primary memory is less than that of secondary memory. Computer memory is used to store two things: i) instructions to execute a program and ii) data. When the computer is doing any job, the data that have to be processed are stored in the primary memory. This data may come from an input device like keyboard or from a secondary storage device

Secondary Memory:
Secondary memory is where programs and data are kept on a long-term basis. Common secondary storage devices are the hard disk and optical disks. This type of memory is also known as external memory or non-volatile. It is slower than main memory. These are used for storing data/Information permanently. CPU directly does not access these memories instead they are accessed via input-output routines. Contents of secondary memories are first transferred to main memory, and then CPU can access it.

Secondary memory is also known as secondary storage or auxiliary storage. The most common type of auxiliary storage devices are magnetic tapes, magnetic disks, floppy disks, hard disks, etc.

Cache Memory:
Cash memory is a special high-speed storage mechanism. It can be either a reserved section of main memory or an independent high-speed storage device. A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used in main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM. The more the cache we have on our computer the more will be the processing speed.