High-level versus low-level. Logical implies a higher view than the physical. Users relate to data logically by data element name; however, the actual fields of data are physically located in sectors on a disk. For example, if you want to know which customers ordered how many of a particular product, your logical view is customer name and quantity. Its physical organization might have customer name in a customer file and quantity in an order file cross referenced by customer number. The physical sequence of the customer file could be indexed, while the sequence of the order file could be sequential.
A message transmitted from Phoenix to Boston logically goes between two cities; however, the physical circuit could be Phoenix to Chicago to Philadelphia to Boston.
When you command your program to change the output from the video screen to the printer, that is a logical request. The program will perform the physical change of address from, say, device number 02 to device number 04. See logical vs. physical topology.
A message transmitted from Phoenix to Boston logically goes between two cities; however, the physical circuit could be Phoenix to Chicago to Philadelphia to Boston.
When you command your program to change the output from the video screen to the printer, that is a logical request. The program will perform the physical change of address from, say, device number 02 to device number 04. See logical vs. physical topology.
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2008 The Computer Language Company Inc. All rights reserved. |
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