Hash Table Emulator

Hash Table Emulator is an interactive macro-enabled spreadsheet model which allows learners to see how a hashing algorithm distributes data records on a hard disc. As the learner enters record key field values, the record appears in the block it is hashed to. Repeat key fields are detected and prevented.

Once a block is full, an overflow pointer is generated, and subsequent records are diverted to the overflow block. This process is repeated if the overflow block itself is filled. The learner can switch between three different hashing algorithms to see how rehashing spreads the distribution of records to reduce overflow.

A second tab shows which records have been entered into the file, and also shows which block each record is hashed to and how many records are hashed to each block for each of the three algorithms. This data is also represented in scaled graphs which accurately represent both the number of records hashed to each block and the number of blocks used.

NOTE: for this spreadsheet to work correctly, the copy of Excel in which it is running must allow macros to execute, and ‘Enable Content’ must be clicked when the spreadsheet is opened.