You could write or read a single sector by ASCII or hexadecimal value from various devices (like hard disk, memory card, compact flash, floppy etc.).
CosmicHexEditor is a simple but useful application for analyzing specific volumes and reading the Master Boot Record data
Data are read by sector (minimum memory allocation unit). Reading data are displayed boot in ACSII and Hex value.
You can operate in deep mode on the unit to learn p.eg. the FAT manage and the differences with NTFS or FAT12 FAT16 FAT32 type, the cluster chain and to restore data also.