Data Transfer Chapter 10

File conversion When we upgrade a file after a big time of use, usually it is necessary to change the format of the file. For example if you use a database that it was created using Access 97 it is necessary to upgrade it by converting it to a file Access 2003

ASCII files It s a text file in which each byte represents one character according to the ASCII code. Contrast with a binary file, in which there is no one-to-one mapping between bytes and characters. Files that have been formatted with a word processor must be stored and transmitted as binary files to preserve the formatting. ASCII files are sometimes called plain text files.text filebytecharacterASCIIbinary file Filesformatted word processorstoredplain text

ASCII vs. Binary Files An ASCII file is a binary file that stores ASCII codes. Recall that an ASCII code is a 7-bit code stored in a byte. To be more specific, there are 128 different ASCII codes, which means that only 7 bits are needed to represent an ASCII character. However, since the minimum workable size is 1 byte, those 7 bits are the low 7 bits of any byte. The most significant bit is 0. That means, in any ASCII file, you're wasting 1/8 of the bits. In particular, the most significant bit of each byte is not being used. Although ASCII files are binary files, some people treat them as different kinds of files. I like to think of ASCII files as special kinds of binary files. They're binary files where each byte is written in ASCII code. A full, general binary file has no such restrictions. Any of the 256 bit patterns can be used in any byte of a binary file. We work with binary files all the time. Executables, object files, image files, sound files, and many file formats are binary files. What makes them binary is merely the fact that each byte of a binary file can be one of 256 bit patterns. They're not restricted to the ASCII codes.

ASCII CODE

Transferring files between word processors Most word processors are capable of reading files from other word processing packages. As a last resort, the original file can be saved in ASCII code which all word processors are capable of reading, but the most of the formatting will be lost (underline, bold, etc)

Data compression Data compression is the technique of reducing the space occupied by a large file. There are many different methods, suited to different types of data. Data compression is particularly useful in communications because it enables devices to transmit or store the same amount of data in fewer bits.

Download Is the term usually used to refer to the transfer of file from one computer to another. Generally the term is used when the user who starts the process is operating the computer that will eventually receive the file. When the user is sending the file to another site, the term used to describe the operation is upload

Overflow Overflow happens when something becomes too large to be processed satisfactory

Digital and analogue computers Digital quantities have values which jump from one to the next without any between value. Analogue quantities have infinitive number of values

Digital and analogue signals