La doc d'EM_write dit:
"
Before each block is a header. It starts with a flag which may be -4 for deleted blocks, -2 for used blocks and -1 for free blocks (AMS 2.xx uses -32 and -64 instead of -2 and -4, I don't know why; maybe old flags may be used for "noname" files, see below). So, if you need to keep some data in the archive memory for a longer time, it must be marked with -2 (or -32 on AMS 2.xx), otherwise it may be treated by TIOS as "free space".
After the flag word, on AMS 2.xx the name of the folder (8 bytes) and the name of the stored file (8 bytes) are stored (both of them are zero padded). After this, yet one word follows (usually set to zero), exact meaning is unknown to me. This extra information (18 bytes) is not present on AMS 1.xx.
"

Je n'étais pas sûr, mais j'aurais dû relire la doc avant de poster.