Sequential datasets are the simplest form or organization of dataset. A sequential dataset contains records placed one after another. A sequential dataset can contain zero records (dataset is empty) or several records. Its size depends only on how much space you provide for it on the disk.

When you read records from a sequential dataset you read the records one by one starting from the first record. This is quite okay for purposes like printing of records, it is not an ideal way for accessing data fast.

For example, if there are 50000 records and you want to access the 30000th record it will take a very long time. The following figure shows the physical representation of a Physical Sequential data set.

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