This improves performance because only 2 bytes have to be compared for each file. When a match is found, the file names are compared to ensure that the proper file was located in case of hash collisions. Each record in the directory is searched by comparing the hash value. When searching for a file, the file name is first converted to upper case using the upcase table (file names are case insensitive) and then hashed using a proprietary patented algorithm into a 16-bit (2 byte) hash value. (If files have longer names, this number will decrease but this is the maximum based on the minimum three-record file set.) To help improve the sequential searching of the directories (including the root) a hash value of the file name is derived for each file and stored in the directory record. This is called a directory file set, and a 256 MiB sub-directory can hold up to 2,796,202 file sets.
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