 Hello Learners, I am Dr. Shruti Sruvaparali, Assistant Professor in the Department of Computer Science and in this video I am going to talk about the primary memory, secondary memory and catchy memory. The primary memory or main memory is the area of computer from which the processor can store and retrieve data very quickly. It is active only when the computer is switched on. Primary computer should have a primary memory which is a temporary storage area built into the computer hardware. Instructions and data of a program reside mainly in this area when the CPU is executing the program. The rate of data fetching from primary memory is about 100 times faster than that from a high speed secondary storage like this. Primary memory consists of some integrated circuit chips either on the motherboard or on a small circuit board which is attached to the motherboard of a computer system. The primary memory is made up of several storage areas called locations or cells. Each of these locations can store a fixed number of bits called world-length of the memory. Each world or location has a built-in and unique number assigned to it. For example, if a memory has 104 locations, then the address ranges from 0 to 1023. We have all heard about 8-bit computers, 16-bit computers and so on. The numbers here refer to the total number of bits per memory word. The main memory capacity is defined in terms of number of bytes a computer system can store. There are two main categories of primary memory. They are random access memory or RAM and the read-only memory or Lone. Random access memory or RAM is used to store data and instructions during the operation of a computer. The data and instructions that need to be operated upon by the CPU are first brought to RAM from the secondary storage devices. RAM loses its information when the computer is powered off. This is a type of volatile memory. When the power is turned on again, all the files that are required by the CPU are loaded from the hard disk to RAM. Since RAM is a volatile memory, any information that needs to be saved for a longer duration of time must not be stored in the RAM. RAM provides random access to the stored bytes, words or larger data units. This means that it requires the same amount of time to access information from RAM, irrespective of where it is located inside it. The size of RAM is limited due to its high cores and is measured in megabytes or gigabytes. RAM typically contains portions of the operating system as well as the applications and data in active or frequent use. A part of the operating system is loaded in the primary memory when the computer is turned on and it stays there until the computer is turned off. RAM is also used for the temporary storage of input data, output data and the intermediate results. The input data entered into the computer using the input device is stored in RAM for processing. Once the processing is done, the output data is stored in RAM before being sent to the output device. Any intermediate results generated during the processing of the program are also stored in RAM. Nowadays, computers with 1GB, 2GB, 4GB or 8GB RAM are available in the market. Read-only memory or ROM is a non-volatile memory chip in which the data is stored permanently and cannot be altered by the usual programs. Once the data has been written onto a ROM chip, it cannot be removed or changed and can only be read. This is the reason why it is called read-only memory. ROM comes programmed by the manufacturer so that it cannot be modified by the users. This means that the ROM stores special micro-programs that permanently reside inside it. ROM can be categorized into manufacturer programmed and user programmed. Let us look at what a manufacturer programmed ROM is. In manufacturer programmed ROM, chips are supplied by the manufacturers of electronic devices and it is not possible for the user to modify the programs or data stored in the ROM chip. Whereas in the user programmed ROM, a user can load and store read-only programs and data. Such a ROM is also known as programmable read-only memory or PROM because the user can program it. The contents of ROM and PROM cannot be altered. We have also another erasable programmable read-only memory or eProm where it is possible to erase the information stored in the eProm chip and the chip can be again reprogrammed to store the new information. But the content of eProm can be erased by exposing it to ultraviolet light and undetend by reprogramming it. Now, let us look at the secondary memory. The secondary memory is also known as secondary storage auxiliary memory or external memory. It is used primarily to store large volumes of data on a permanent basis for a longer period of time in the computer system. This data can be partially transferred to the primary storage whenever it is required for processing. The secondary storage does not lose any data when the computer is powered down. It is non-follietile and has lower cost per bit stored as compared to the primary storage. But it generally has an operating speed far slower than that of the primary storage. The secondary storage differs from primary storage since it is not directly accessible by the CPU. The most common form of auxiliary memory devices used in the consumer systems are flash memory, optical disk and a magnetic disk. Next is the catching memory. The catching of data by the CPU from the main memory does about 100 times faster than that of a secondary storage. The main memory helps in minimizing the mismatch of processor disk speed to a large extent. But even then, there is a mismatch of speech between the processor and memory. The rate at which the data can be fetched from the memory is about 10 times slower than the rate at which the CPU can process the data. Catching memory is used to overcome this problem as it minimizes the processor memory speed mismatch. Catching memory is an extremely fast, small memory between the CPU and the main memory, whose access time is closer to the processing speed of the CPU. It is used to temporarily store very active data and instructions during processing. It is made up of static RAM and it acts as high speed buffer between the CPU and the main memory. Thank you for listening to this video.