All about CRAM Files

The CRAM file type is primarily associated with samtools.

CRAMFile Extension CRAM
File extension: CRAM
File type:  compressed file format

What is a CRAM file?

CRAM files mostly belong to samtools. CRAM files come in two main forms:
Genomic data: These files are compressed BAM files that store sequence alignment records using reference‐based compression. They reduce storage needs for large genomic data sets. Use specialized tools like samtools to view and convert them. More details are available at HTSlib.
ROM file systems: A smaller group of CRAM files are compressed ROM File System files used to keep a compact image of a file system in embedded devices.
Key details provided by FilExt.com:
  • Data type: Stores genomic sequence data or ROM file system images.
  • Function: Uses compression techniques to reduce file size while maintaining data integrity.
  • Usage: Applied in bioinformatics for sequence alignment and in embedded systems for ROMFS images.
  • FilExt.com note: These files require specific software to extract and inspect their contents.

    How to open a CRAM file

    You need a suitable software like samtools to open a CRAM file. Without proper software you will receive a Windows message "How do you want to open this file?" or "Windows cannot open this file" or a similar Mac/iPhone/Android alert. If you cannot open your CRAM file correctly, try to right-click or long-press the file. Then click "Open with" and choose an application. You can also display a CRAM file directly in the browser:. Just drag the file onto this browser window and drop it.

    Online CRAM Text Viewer

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    Programs that open and convert CRAM files:

    1. samtools
      See the previous paragraphs to learn more about the main application. CRAM files are often referred to as samtools compresseds because this type of file is primarily created or used by this software.
    2. Compressed ROM File System
      In UNIX/Linux variants you use mkcramfs to create a .CRAM file which is a compressed ROM file system image from the contents of a given directory. Cram file systems are used for Debian INITRD images.

    Technical Data for CRAM File Extension

    File classification:
    Compressed
    Related files:

    a cram compressed file format is a special file format and should only be edited and saved with the appropriate software.

    How to solve problems with CRAM files

    • Associate the CRAM file extension with the correct application.
    • Update your software that should actually open compressed file formats. Because only the current version supports the latest CRAM file format. Search, therefore, e.g. on the manufacturer website after an available samtools update.
    • To make sure that your CRAM file is not corrupted or virus-infected, get the file again and scan it with Google's virustotal.com.
    • Click here to open your .CRAM file online - secure, fast, and no downloads needed.
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