Classic Computer Magazine Archive ANTIC VOL. 4, NO. 10 / FEBRUARY 1986


Speedy, convenient DUP.SYS loading

by Scott Fick

Speed up the loading of DUP.SYS in your 64K-or-more XL/XE computer, with Instant-DOS, a fairly short BASIC modifications of Atari DOS 2.5. Instant-DOS stores DUP.SYS plus a MEM.SAV file in the normally unused top 16K of memory. Both DOS functions are rewritten to allow instant loading of DUP.SYS. Also, MEM.SAV is always active to protect your program in RAM. Note: Instant-DOS is not compatible with Antic's DISKIO and DISKIO PLUS DOS enhancements.

If you own an Atari XL or XE computer and use DOS 2.5, you may be getting tired of enduring the long wait for DUPSYS to load in. The cure for this affliction is Instant-DOS. After you install this modification to DOS 2.5, simply type DOS from BASIC and the DUPSYS menu is there. Instantly! With the MEM.SAV file included, your resident program is safe in memory when you return.

The BASIC program is relatively short. Once Instant-DOS is installed, you can forget about it. Type the program carefully-particularly the data. And be sure you understand the following instructions before you proceed!


Type in Listing 1 and check it with TYPO II, then SAVE a copy or two. Don't RUN it yet!

When you're sure that Listing 1 has been correctly typed in – and your system is operating under DOS 2.5 – then LOAD and RUN Listing 1. After reading the data, the listing will create a machine language object file called MODIFY.OBJ.

Now press [BREAK] to halt Listing 1, then type DOS to get to the DOS menu. If you have a MEM.SAV file on your disk, delete it now.

For LOADing MODIFY.OBJ, type [L][RETURN], then type MODIFY.OBJ [RETURN]. After it has LOADed in, press [RETURN] again to get to the menu. You should see that the second line of the menu has been modified to read I-DOS in inverse letters.

We're almost there. Insert a blank disk and format it with DOS option [I]. When formatting is complete, write your new, modified Instant-DOS to the disk by typing [H] [RETURN], followed by the number of the drive containing the new disk. This disk now contains a working copy of Instant-DOS.

IMPORTANT: Turn off your computer and re-boot your system before proceeding. Because of the way MODIFY.OBJ is currently installed in memory, your computer will crash if you go to BASIC and then attempt to return to DOS. This only occurs when first creating Instant-DOS. You won't have to worry about it in the future.


To use your new Instant-DOS, boot the computer using the disk you have just created. You may notice the boot time is a little longer than usual. This is because DUP.SYS is also loading into memory.

When the READY prompt appears, you can type in a BASIC program, then type DOS and press [RETURN]. The DOS menu will appear instantly.

Check the disk directory and you will find nothing listed but DOS.SYS and DUP.SYS. But MEM.SAV is working. Type B to return to BASIC and you will find your BASIC program is still in memory.

You can make copies of Instant-DOS by using the H option from the Instant-DOS menu. This time around, you won't have to bother re-booting the computer to avoid crashes.

Scott Fick is from sunny Palm Bay, Florida and Instant-DOS is his first published Antic program.