Bitmaps (File architecture)
Bit Maps are used throughout Model 204 to track sets of records.
The Workings of a Bit Map
The page size in Model 204 of 6184 bytes contains 6144 'usable' bytes (along with its 40 byte trailer).
Usages
Manipulating Bit Maps
Example
In this example (which looks at a bit map as used by an index), this is the beginning of the bit map representing the ORD CHAR field value pair COLOR = BLUE for the 3rd segment of a file (which covers IRNs 98304 to 147455).
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Based in this, record 98304 does not have an occurrence of COLOR = BLUE, but records 98305 and 98306 do... and so on.