DDA@CMU-CS-C.ARPA (12/09/83)
From: Drew Anderson <DDA@CMU-CS-C.ARPA> On a "normal" implementation of CP/M (8", SSSD 128byte/sector,) can your CP/M80 system read and write CP/M86 disks? I would assume that this would be true, but the guys at Priority One Electronics said no. Drew Anderson DDA@cmu-cs-c.arpa -------
George.Wood%cmu-cs-a@sri-unix.UUCP (12/10/83)
While the disk formats, i.e 8", sssd, 128 byte/sector, can be used by both cp/m-80 and cp/m-86, they have different directory structures. I don't know the specifics, but I think '86 keeps the date of the last file modification with the directory entry. If you can figure out the directory format for '86, you should be able to read & write with DUU; but it would probably be exasperating. It seems to me that a conversion program could be built by around duu -- any takers? George (ps: I'd appreciate pointers to more info on the cp/m-86 directory structure)
ciaraldi@Rochester.ARPA (12/10/83)
From: Mike Ciaraldi <ciaraldi@Rochester.ARPA> I have successfully read and written CP/M-86 disks on a CP/M-80 system, and also on an MP/M-80 system. The file and directory formats are exactly the same, with one exception, which is very important. CP/M-86 has an optional extension to the directory that allows you to store extra information about each file, such as date and time stamps, passwords, etc. This is the same as used in MP/M. Physically, it uses extra directory entries. Ordinarily, CP/M-80 uses one directory entry per file, unless the file is long, in which case it uses additonal directory entries with the same file name and different status bits to hold the pointers to the rest of the file. In MP/M and CP/M-86 you can tell the file system (using the STAT or SET command) that a particular diskette will have XFCB's (extended File Control Blocks). If you do, the OS uses an extra directory entry for each file. It has the name of the file and certain status bits to show it is an XFCB. In the rest of the directory entry, (where you would ordinarily find pointers to disk blocks) are the time stamps, etc. There is also one more special directory entry which can store the name of the diskette and its attributes (e.g. whether to have XFCB's, whether to timestamp all files, etc.) The result is that MP/M, CP/M-86, and Concurrent CP/M-86 disks are "upward compatible" from CP/M-80. The three newer operating systems can read and write CP/M-80 disks, because to them the disks look like disks that have not been labelled and have not had the extended features activated. But, the CP/M-80 system may get confused when it reads and writes the disks from the other three. As long as the diskette does NOT have the extra stuff activated (which is usually, but not always, the way the format program leaves a blank disk), CP/M-80 is happy. But if it tries to use a disk with the extended stuff activated, it may mess up. The new version of CP/M-80, called CP/M-Plus or CP/M 3.0, has these extended file things. All clear? Boy, I hope I got this all right... Mike Ciaraldi ciaraldi@rochester