Classic Computer Magazine Archive CREATIVE COMPUTING VOL. 11, NO. 8 / AUGUST 1985 / PAGE 100

Everything you always wanted to know about disk drives and DOS. (Outpost: Atari) David Small; Sandy Small.

One of the most perplexing problems for Atari novices (and some experts, too) is the proliferation of disk drives and disk operating systems currently in use. Compatibility is the basic question, and although I know that many of you have your disk systems up and running, I also know that there are probably just as many who would like to upgrade, but don't know where to begin. So let's find out.

There are three types of disk drive for Atari computers. The 810, Atari's original release, is a single density drive that offers 18 sectors per track and 128 bytes per sector. With 720 sectors per disk, it has a capacity of 92,160 bytes.

The 815 is a double density drive that offers 18 sectors per track and 256 bytes per sector. It has the same 720 sectors per disk and a capacity of 184,320 bytes. The 815 was announced but never released; nevertheless, many third party manufacturers adopted the 815 format, so it is quite popular, despite never having been released by Atari.

The 1050, Atari's current model, is a "dual" (not to be confused with "double") density drive with a capacity of 133,120 bytes in 1040 sectors. It has 26 sectors per track and 128 bytes per sector. Atari tells us that in this case, "dual density" really means "enhanced density."

When it comes to actually using one or more of these drives, many people become confused because the 815 and the 1050 have dual personalities. Each has its native mode, but both can also be made to emulate the older 810. So, in general, the 815 and the 1050 can both read and write disks that work on the 810. Apart from the 810 mode, compatibility among the three drives is all but nonexistent (see Table 1).

DOS Update

On top of all this we have the confusion surrounding the various incarnations of DOS for the Atari. When Atari designed the 815, they created a new DOS called DOS 2.0, which could read both 810 and 815 disks. DOS 2.0 was set up to handle either the 128-byte, single density format of the 810 or the 256-byte format, double density format of the 815. In either format, it is restricted to 720 sectors.

Indus, Percom, and other third party manufacturers incorporated this true double density mode in their drives. Some supply their own DOSes, like SpartaDOS and MyDOS, to handle different sector sizes, but all are derivatives of DOS 2.0.

Then Atari released the 1050 with its completely nonstandard dual density mode and DOS 3.0--a slow, buggy operating system that cannot handle 815 formats.

Now, as we discussed last month, we have the new, improved, if somewhat retroactive sounding, DOS 2.5. Table 2 describes current DOS/drive compatibility. Two things are important to note. First, DOS 2.5 has no provision for handling 256-byte sectors. This means that there is no way to read true double density disks with third party drives using DOS 2.5. Likewise, if you have installed the US Doubler in your 1050 to make it truly double density, you will not be able to read double density disks with 2.5. I hope someone comes up with a patch soon.

Second, the 1050 has 1040 sectors. DOS 2.0 is limited to 720 sectors. Hence, you will be able to use only 720 of the 1050 disk sectors if you use DOS 2.0 with the 1050.

In addition to redressing the shortcomings of DOS 3.0, DOS 2.5 compensates for some of the design flaws in the 1050 drive. It is cleverly designed to allow you to transfer information between an 810 format disk and a 1050 disk. How? DOS 2.5 ensures that all files in the "extra" sectors (sectors 721-1040) are set apart by themselves. Thus, when you copy a 1050 disk onto a 810 disk, only the files that fit are transferred.

New Utilities

DOS 2.5 also supplies a new DOS menu option: P to format disks in single density (or 810) format. If you format a disk using the normal I option, you will get 1050 format; if you use the P option, you get 810 format. So, you see, the operating system automatically compensates for the split personality of the 1050.

(Note for beginners using double density: If you get an Error 139 or Error 143 message, your drive is probably in a different density than the operating system thinks it is in. For example, the drive might be sending 256-byte sectors to a computer expecting 128-byte sectors. There are various methods, depending on the DOS and drive involved, for making sure they match. DOS XL, for example, with Percom, Indus, and ATR-8000 drives includes a utility called CONFIG, which forces the drive into the correct density.)

DOS 2.5 also comes with a utility, called COPY32.COM, designed to copy files from DOS 3 format to 2.5 format. To use it, get to the DOS menu (type DOS from Basic) and then type L to load a binary file. Next, type the binary file name COPY32.COM and follow the directions that appear.

Another utility, SETUP.COM, loaded as above, tells the operating system how many drives you have connected, how many file buffers you want open, and so on, in a friendly, menu-driven format. With DOS 2.0, you had to do some bizarre PEEKS and POKES to accomplish the same thing.

The FIXDISK utility that comes with 2.5 is not the old Atari Disk Fixer, which was a powerful super zap utility that beginners found perplexing. Rather, it is a friendly way to do things that beginners often need to do to disks, such as unerase them.

The last supplied utility is called RAMDISK, which sets up Drive 8 as a RAMdisk in the extra memory of the 130XE--if you have a 130XE. If you have RAMDISK.COM on your disk when you boot up with DOS 2.5, the disk will load automatically. At that point, D8: is a high speed disk drive, simulated in the extra 64K of memory in the 130XE. It has 499 free sectors available. When initialized, the RAMDISK gives you a "fast load" into the DOS menu and a free MEM.SAV, which prevents you from losing what you were doing when you typed "DOS."

Note: One "design feature" (bug?) of the RAMdisk is that you cannot "duplicate disk" into it. I gives no warning; it just doesn't work. You must use C(opy)*.* instead.

Remember that the RAMdisk has only 64K of memory available and that a standard Atari disk has much more than that. If you disk is more than two-thirds full, it will not fit entirely into RAMdisk. Keep this in mind when you see the Disk Full message.


Now that you have a good working knowledge of the idiosyncrasies of Atari disk drives, let's take a look at another minor problem that sometimes plaques new users. If you have one of the new XL/XE machines, your computer has Basic built in (the older Ataris did not). Basic is what comes up when you turn the machine on unless you specifically tell it you want something else by holding down the Option key when you switch the machine on.

Why would you not want Basic? Well, because many programs will not work when Basic is present; both Basic and the program try to use the same section of memory. So, if you buy a program and can't get it to load properly, try disabling Basic.

If it still doesn't work, you might need a Translator disk--a copy of the old operating system that came with the 400/800 machines, the machines for which a great deal of the software currently available was written. The Translator disk allows your softwaree to believe that it is being loaded into an Atari 400 or 800.

How can you get a Translator disk? Probably the best way is from a user's group. Call David Duberman at Atari (408-745-5405), and ask him for the name of a user's group in your area. Most active user's groups have copies of Translator and will be happy to share with you.

If even translator doesn't get your program up and running, check to see whether the software uses joystick ports 3 and 4, which were built into older machines but have been omitted from the XL/XE series. Atari Asteroids is an example of this.

I hope these tips will give beginners and old hands alike a better understanding of Atari disks and DOSes and keep you all computing creatively until next month.