Classic Computer Magazine Archive START VOL. 3 NO. 2 / SPECIAL ISSUE #4


How Fast Is Your Floppy Drive?

By Dave Small with Dan Moore

Avoid speed traps with SPEED.ARC on your START disk!

This issue, we'll take a look at how fast your ST's floppy disk drives are spinning--and why it's important to you. Why should you care about how fast your drive spins? If you'll allow me a little diversion, I'll tell you.


Atari ST disk drives are supposed to turn at 300 RPM. In fact, they're supposed to be locked onto 300 RPM. 3 1/2-inch disk drives feature a feedback mechanism that keeps the disk spinning to within 1 percent of their preset speed.

When I worked at Data Pacific I made a big mistake on the original release of the Translator One disk controller. This device lets Atari drives read and write Macintosh disks when used with the Magic Sac cartridge, and I originally relied on Atari drives running at 300 RPM. The Mac, you see, is very touchy about its data rate, which is directly related to disk speed.

Big error. About 50 percent of the first Translators wouldn't format their owners' disks. This turned out to be drive speed troubles. We issued a quick-and-dirty speed tester, and found the ST drives running at speeds from 285 to 315 RPM--as much as five percent off! Needless to say, I had to hustle out a quick revision to the Translator that no longer trusted in 300 RPM.


SPEED.PRG, on this issue's START disk, is an updated (and lots nicer) version of my original "hacked" disk speed tester. Why use it? Well, if you don't test your drives, you'll be able to read and write disks all day on your ST. But those times you take a disk to a friend's house . . Well, if your drive ran at 290 and Ralph's drive is running at 310, you could have big problems. For instance, you might copy a file to your disk and end up destroying the disk, because the sectors would be too "short" for a 310 RPM drive

Also, when you write disks for your "permanent archive," you want them just as close to perfect as possible, so any ST you try to read them on will have the best possible chance of reading them.


To use the speed tester, boot in medium or high resolution. Un-ARC the file SPEED.ARC from your START disk, following the Disk Instructions elsewhere in this issue. Next, double-click on SPEED.PRG, then select the drive you'd like to check. (That drive will need a diskette in it; don't worry, we won't try to reformat it or anything, and you can write protect it, if you like.)

If your drive is between 295 and 305 RPM, you're probably okay. Note that I say "probably," not "definitely." You can get into trouble above 305 RPM very quickly because of the floppy disk controller's design.

You may want to let this test run awhile to check speed drifting, typically caused by the diskette heating up while spinning. (No kidding!)

Click on Quit to stop the test, or click on a drive letter name to test the other floppy. Click on Quit again to exit to the Desktop.


Okay, what should you do if your drive is way off RPM? Take it to your dealer and get it fixed. Don't bother trying to fix it yourself. Why do I say this? Because as far as I know, these things aren't adjustable; I have yet to see an ST drive with a speed adjustment control in it.

Remember, ST floppy disk drives are designed to run at 300 RPM, and a circuit is in there specifically to do that. Put yourself in the engineer's shoes: Why should they need a speed adjustment control? (Of course, ST drives have a little problem with reality.)

So let the dealer fix it, okay? They'll probably just swap mechanisms, then give it back to you.

The disk speed tester is not a conclusive test of the drive, of course; it's meant to measure one of several variables of a disk drive. There are also alignment and hysteresis tests a dealer can run. But the speed tester will help to keep you from writing disks you'll never be able to read again.

A side note: There are several "11-sector" formatters in the public domain. They put 440K per side of the disk. The problem with 11-sector format is that they won't work on drives that run faster than about 305 RPM--and there're a lot of faster-than-305-RPM drives out there. This is why we struck with 10 sectors on the Twister format: it left plenty of tolerance on either end of the track. If an index pulse occurs durig a sector read, you'll get an automatic CRC error on that sector, period; the WD 1772 (the ST's disk controller chip) has that bug in it's design. Eleven sectors at 305 RPM means your 11th sector is right next to the index pulse; go any faster, and it will be during the index pulse.

Also, the programs that format 81, 82 or even 83 tracks are pretty questionable. While they may work on your drive, they may not on a friend's. In particular, Atari has started shipping disk drives with 8048 microprocessors in them; the 8048 chip is there to "buffer," or slow down, the step rate from three milliseconds per track (ST rate) to six milliseconds per track (drive rate). The 8048 is smart enough to know not to let the head past track 80. Thus, you could write disks on one drive out to track 83, put them into another drive, and never be able to reread that data.

Besides all this, the highest numbered tracks are the worst area for data separation. Your floppy disk controller is fighting for its life in this area; most drives that have trouble have the most trouble on these innermost tracks.

Is the extra room worth all this hassle?


Next issue. well present a very simple, very useful program that makes sure none of your disks have gone bad.

Dave Small is the creator of the Magic Sac Macintosh emulator and the Translator One disk controller, the author of three books and many computer magazine articles. Dan Moore is the author of PaperClip for the Atari 8-bit computers.