On Fri, 26 Jul 2002 08:46:57 +0100, Luke Trevorrow <[EMAIL PROTECTED]> wrote:
>>> Why does BDOS work on a floppy by floppy basis? Is it some limitation with >>> the SAM Coupe that stops you from having one big disk like on a PC? >>> >> Yes, the disk directory structure is fixed to expect 80 tracks of 10 >> sectors or 510 bytes. There is a 195 byte (1560bit) area in each file >> header which holds a bit map of the sectors used by that file. >> >> To avoid the need to create a new more complex directory structure >> (like what HDOS did) BDOS just maps the hard disk as many floppies. >> > I take it that because you mention HDOS that it is possible? Sort of. I am talking REAL SAM here not Simcoupe. Not many people remember HDOS, as it was the runner up in the hard disk race to BDOS. People like BDOS as you could (can) install the hardware and load and run your existing programs with no changes. This was not the case with HDOS. Although some disk functions were the same for compatibility reasons eg LOAD, SAVE, OPEN, CLOSE, etc. many others were not. For example READ AT <d>,<T>,<S>,<adr> wouldn't work in HDOS as the hard drive was simply an array of sectors starting at 0, the disk label, and continuing to a theoretical maximum of 2^32-1 or in reality 1 sector short of the disk capacity. So stuff like this was done from BASIC with a CALL command. The directory was completely different, it was a new structure that I created just for HDOS which should have allowed all the space on a drive to be used without any significant loss of performance as it fragments and with no practical limits on directory or file size. (OK I'm droning on but it was my baby for almost a year). It did however suffer from hardware problems. Many drives just would not work or were unreliable and the hardware had to be recalled for a free upgrade to fix a buffering problem. Rather than making me rich I damn near went broke because of it :-( The final straw was a major failure of the PC I was developing on and the discovery that the backup tape was corrupt and wouldn't read. Faced with a data recovery bill of ~£10K I had to call it a day as I couldn't bear the thought of starting over, and I bought back many of the units as, well I'm just a nice guy. I remember that I was able to create and use random access files of >4Gb with calls (something like) CALL <routine>,<stream>,<record num> but as nobody wanted to use SAM to create and use large file databases .... yawn Zzzzz zzzz zzzz zzzz Nev - who has almost finished scanning the tech manual.
