APPENDIX SEVENTEEN ________________________________________________________ DOS 2.5 And The 1050 Drive The latest version of DOS (Disk Operating System) for the XL and XE computers is 2.5. It offers several advantages over the earlier ver- sions (including the ill-received DOS 3.0), including dual-density formatting, new XIO formatting commands available from BASIC, a RAMDISK program for the 130XE, and greater compatibility with DOS 2.0. If you use DOS 3.0, I suggest you get a copy of 2.5 as soon as you can. DOS 2.5 formats a track with 26 sectors instead of the 18 DOS 2.0 han- dles; this means a disk with 1010 sectors free instead of 707 (leaving 931 free sectors with DOS and DUP.SYS files on a disk). The 1050 (not the 810) drive can automatically sense which density the disk in the drive is using. DOS 2.0 can read a 2.5 disk but the additional sectors are invisible to it. New BASIC Commands for DOS 2.5 When you OPEN a disk from BASIC to get a directory read (see loca- tion 1792; $700 in the Addenda section), you normally use OPEN #1,6,0,"D:*.*." Now, if you use OPEN #1,7,0,"D:*.*," DOS will specify files which occupy disk sectors that can't be accessed by 2.0 with angle brackets, like . These files are invisible to DOS 2.0 when reading a directory; they can't be loaded, nor do they show up in the directory. Formatting the disk by the XIO command is enhanced. The usual method is XIO 254, #1,0,0,"D1:." This will format the disk, trying first for dual density, and if the drive doesn't support it, formatting in single (2.0) density. XIO 253, #1,0,0,"D1:" formats a disk with single density only (a new option--P--has been added to the DOS menu to format in single density as well). XIO 253, #1,34,0,"D1:" will format a disk in dual density only. RAMdisk for the 13OXE DOS 2.5 includes a special program called RAMDISK.SYS. This loads up when the disk is booted and determines if your computer is a 130XE. If so, it runs a small program which creates a "disk drive" out of the 64K extended memory bank. The RAMdisk acts just like a real disk, except that it's faster. It is formatted into 499 sectors and a direc- tory and has the drive number D8:. DOS 2.5 supports drives 1-8, but is initialized to drives 1, 2, and 8, so if you have other drives, change location 1802 ($70A); that is, if you have three drives and the RAMdisk, POKE 1802, 135. All bits in location 1802 now represent pos- sible drives. When it runs, RAMDISK.SYS copies MEM.SAV and DUPSYS to the RAMdisk, then modifies a location so that you call up DUP.SYS from