Hence the rate of data fetching from the main memory

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Unformatted text preview: gram(s) the CPU is currently woi*king on? The time to fetch and load data from this storage space into the CPU registers must also be very small as compared to that for disk storage to reduce the speed mismatch problem with the CPU speed. Every computer has such a storage space, which is known as primary storage, main memory, or simply memory. It is a temporary storage area that is built into the computer hardware and in which instructions and data of a program reside mainly when the program is being executed by the CPU. Physically, this memory consists of some chips either on the motherboard or on a small circuit board attached to the motherboard of a computer system. This built-in memory allows the CPU to store and retrieve data very quickly. The rate of fetching data from this memory is typically of the order of 50 nanosecond/byte. Hence the rate of data fetching from the main memory is about 100 times faster than that from a high-speed secondary storage like disk. Storage Evaluation Criteria Any storage unit of a computer system is characterized and evaluated based on the following properties: 1. Storage capacity. It is the amount of data that can be stored in the storage unit. A large capacity is desired. As compared to secondary storage units, primary storage units have less storage capacity. 2. Access time. This is the time required to locate and retrieve stored data from the storage unit in response to a program instruction. A fast access time is preferred. As compared to secondary storage units, primary storage units have faster access time. 3. Cost per bit of storage. This refers to the cost of a storage unit for a given storage capacity. Obviously, a lower cost is desirable. As compared to secondary storage units, primary storage units have higher cost per bit of storage. 4. Volatile. If the storage unit can retain the data stored in it even when the power is turned off or interrupted, it is called non-volatile storage. On the other hand, if the data stored are lost when the power is turned off or in...
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