Measuring storage, units of information.
Measuring Storage - Sequences of bits whose value can be zero or one, can represent all information. Bits can represent letters, numbers and other characters. Codes that use only seven bits can represent 128 different characters. Two coding systems that use eight bits have become industry standards. ASCII code (American Standard Code for Information Interchange) - Most PC use a code called ASCII to represent characters.
EBCDIC (Extended Binary Coded Decimal Interchange Code) - IBM uses a code called EBCDIC for its largest computers. Some other manufacturers too. Byte - Because of the historical widespread use of these eight-bit coding schemes, we measure storage capacity in bytes, where one byte equals eight bits. Have been increasing or plan to increase their data storage by >33% a year. Some of them grow by 50% a year. Wal-Mart’s data warehouse held 7.5 terabytes of the company inventory, forecast, customer, competitor, and market basket information in 2001. Types of storages. Primary storages of information. Examples Types: Primary or secondary Volatile or non-volatile Primary storage is electrical, resides on the bus, and is directly accessible to the processor. Examples: Cache Memory - Describes a small amount of primary storage that is faster than the rest of the primary storage in a computer. ROM - Read Only Memory retains its state in the absence of electrical power to hold the computer’s initial instructions.ROM devices do not change their state in response to an electronic signal; data must be burned into ROM memory using special equipment. Because of the expense of ROM and because data on ROM cannot be changed, computers contain only kilobytes of ROM compared to megabytes of RAM RAM - Random Access Memory loses whatever data it has if someone turns off the computer without any data or programs in its memory the computer could not do anything when turned on. 22. Types of storages, secondary storages of information. Examples Secondary storage is storage that the processor cannot access directly. When the processor needs data, it commands the controller to obtain the data from the secondary storage device and place it on the bus. The processor then uses the data immediately or keeps it in primary storage. Types of storages. Volatile and non-volatile storages. Examples. Volatile storage requires electrical power to retain its data. Non-volatile storage retains its data even in the absence of electrical power. 27?28?29 – examples:
Advantages of secondary storages over primary. Access to data in secondary storage occurs at speeds several thousands to a million times slower than access to data in primary storage.
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