Atari 8-bit disk images

Drop an .ATR or .XFD image (or use Open). The tool reads the header, shows the geometry (single, enhanced, or double density), and decodes the directory.

VTOC shows which sectors are free and which are used.
Files lists the directory with each file’s flags, size in sectors, and start sector. Click a file to follow its sector chain: you get its bytes, a text view (ATASCII with $9B end-of-line converted to newlines), and — for executables — the binary load segments with their load addresses and any RUNAD/INITAD vectors.
Download saves a file, as raw bytes or as converted text.
The sector viewer shows any sector in hex with ATASCII alongside.

Format notes

ATR: a 16-byte header — magic $0296, image size in 16-byte paragraphs, sector size — then the sectors. On double-density disks the first three sectors are 128 bytes unless the image pads them to full size.
XFD: raw sectors with no header; the density is guessed from the size.
DOS 2.0/2.5: the VTOC is sector 360 (a bitmap, most-significant bit first, 1 = free) and the directory is sectors 361–368: 64 entries of 16 bytes (flag, sector count, start sector, 8 + 3 name). The last three bytes of each data sector hold the file number, the next sector, and the number of bytes used. DOS 2.5 adds a second VTOC at sector 1024 for enhanced-density disks. MyDOS drops the file number so it can address more sectors.
Binary load files start $FF $FF, then segments of start address, end address, and data. A segment covering $02E0 sets the run address; $02E2 an init address.

ATASCII graphics characters are shown with Unicode look-alikes, not the Atari ROM font. SpartaDOS file systems are not decoded.

Works with

Format notes