FAT file system now licensed by MS ?

Jerome Fine replies: Since RT-11 is still actively used, a set of DOCs can still help anyone who is interested. Assuming that RT11 actually means RT-11 based originally on DEC (Digital Equipment Corporation) PDP-11 computer systems, then a brief review of the RT-11 file structure might be helpful. (a) RT-11 does NOT use a FAT!!!!!!!!!!!!!!!!! (b) While block ONE for a file structured device does contain some additional directory information, it is not normally required for directory operations. (c) Block 6 is the start of the directory for ALL random access file structured media. Note that while block 1 contains a word that has 6 as the value that is nominally used to point to block 6, so many RT-11 programs ASSUME that block 6 is the start that it is no longer possible for any other block to be used. (d) The file structure is based on directory segments. (e) Each directory segment is EXACTLY 2 blocks in size or 512 words of 16 bits. (f) The RT-11 command to set-up an RT-11 file structure is "INITIALIZE dev:" and this command is totally separate from the FORMAT command which deals ONLY with the LLF (Low Level Format) of a disk drive or the media in the case of removable media (with certain exceptions that most users would not appreciate - including the fact that probably most media can't be FORMATed FORMAT command does NOT include setting up the RT-11 file structure. For DOS/Windows people, this usually causes GREAT confusion!!!! (g) All file space in an RT-11 directory is accounted for via entries within each directory segment - including areas that are NOT yet allocated that are noted in the status word as being just that - UNUSED. (h) Each freshly initialized RT-11 file structure has exactly one directory segment which contains exactly one file entry for all of the UNUSED blocks on that random access device. There are a maximum of 31 directory segments allowed (some RT-11 file structures for devices that are small such as floppy media allow for many fewer than 31 segments. (i) Each directory segment has 5 words at the start: o Maximum Number of Directory Segments o Next Directory Segment - Zero if the Last o Total Number of Directory Segments in Use - ONLY maintained in Directory Segment #1 o Number of Extra Bytes in Each File Entry o Starting Block Number of First Area which means the maximum device is 65535 blocks (RT-11 does NOT check to verify that this value is correct and follows immediately after the previous file entry in the linked list - thus it is possible to successfully "fool" RT-11, but this is STRONGLY against ALL rules and should not even be considered EXCEPT for READ ONLY MEDIA such as a CD - and then ONLY in special cases!) (j) Each File Entry is Composed of a Minimum of 7 words - extra WORDS are allowed o Status Word - File Entry Type (see k below) o 3 words of RAD50 file name (2) and type (1) o Number of Blocks in the File Entry which means that the maximum file is 65535 blocks o Used for TENTATIVE File Entries - used by TSX-PLUS for file times for PERMANENT files - proposed for use for Y10K dates o Creation Date (01-Jan-1972 up to 31-Dec-2099) o Extra WORDS are used by user programs as specified by Number of Extra Bytes (ALWAYS EVEN) in Each File Entry (k) The are (currently - and probably this will NEVER change) ONLY three types of space: o UNUSED - (1000) the space is available o TENTATIVE - (400) the space has been requested o PERMANENT - (2000) the space has been allocated o END OF FILE entries (4000 - only ONE word is then required for the whole file entry) (l) The maximum number of file entries in each directory segment is 72 [=(512-6)/7]. (m) All file entry blocks are contiguous by definition which means that all files are contiguous. Files can be "extended" only if the immediately following file entry is UNUSED and has sufficient blocks available - this is rare and can't be relied upon in most cases. Since the above is already TOO much detail, I will not mention how files are allocated by the USR (User Service Routine) along with how extra directory segments are created. Any questions are welcome! Sincerely yours, Jerome Fine -- If you attempted to send a reply and the original e-mail address has been discontinued due a high volume of junk e-mail, then the semi-permanent e-mail address can be obtained by replacing the four characters preceding the 'at' with the four digits of the current year.