Systems and methods for CRAMFS file system differencing and updating are provided that include portion-level differencing and block-level updating of blocks of an original image. The differencing and updating split CRAMFS images into portions using CRAMFS file system structure information and block information and perform dependency analysis using hint/list files from the CRAMFS split module. A delta file is generated for each portion (portion-level differencing) of the new CRAMFS image; the delta file includes information of differences between the portion of the new CRAMFS image and the portion of the original CRAMFS image to which the new CRAMFS image portion corresponds. The delta files are transferred to a device where the device target CRAMFS image is updated block-by-block using information of the delta files. The update reconstructs all portions of the new CRAMFS image in a block in host device RAM and writes the reconstructed block into host device ROM.