Additionally each column in the SAM format is separated into its own blocks, improving compression ratio.
CRAM files typically vary from 30 to 60% smaller than BAM, depending on the data held within them.
[7] The basic structure of a CRAM file is a series of containers, the first of which holds a compressed copy of the SAM header.
Selective decoding may also be achieved using the Compression Header to skip specified data series if partial records are required.
CRAM version 4.0 exists as a prototype in Scramble,[5] initially demonstrated in 2015, but has yet to be adopted as a standard.