APPENDIX SEVENTEEN



the RAMdisk rather than D1:. This brings up DOS almost immediately
when you leave BASIC. However, if you want to delete DUP.SYS from
the memory drive and call it up from drive 1 as usual, type POKE
5439, ASC("1"), this points DOS back to the original drive. You can
also delete MEM.SAV from D8: if you don't need it.

DOS 2.5 Boot Sector and Memory Map
Locations 1792-1812 ($700-$714) are loaded directly into RAM from
the boot sector (sector 1) on a disk. Refer back to the section in the
400/800 memory map tar more explanation. These are from an article
by Neil Harris in the Atari Explorer; they are locations Atari promises
to support in the future:

1792           700            BFLG
     Boot flag; always equals 0.

1793           701            BRCNT
     Number of sectors in the disk boot; three--the first three on the
     disk.

1794,1795      702,703        BLDADDR
     Boot load address; where DOS is loaded into memory; always
     1792 ($700).

1796,1797      704,705        BINTAD
     DOS initialization address; always 5440 ($1540).

1798-1800      706-708        BCONT
     JMP instruction to jump to the address where the boot program
     continues execution; 1812 ($714).

1801           709            SABYTE
     Maximum number of concurrently open files--usually three.

1802           70A            DRVBYT
     Drive allocation byte; one bit per drive.

1803           70B            SAFBFW
     Unused.

1804,1805      70C,70D        SASA
     Buffer allocation address for drives and files.

1806           70E            DFSFLG
     Reads zero if there is no DOS.SYS on disk, nonzero if present.

1807,1808      70F,710        DFLINK
     Points to first sector of the DOS.SYS file.