Think about the last time you felt like shooting your cabinet full of 2400-foot computer tapes. Did you catch yourself wanting to blow up, say, Brand X Corporation? Tapes can be too short or poor in quality. So, how can you pick a good tape from a bad one? What is the explanation for short tape and write skips? TOO SHORT? TOO BAD. You were trying to back-up data again, and your blank tape, even though it was the same brand as the original, was too short.

It seems strange, you think, that the information that fit on one tape, somehow doesn't fit on another. Meanwhile, the only way to know if a tape is long enough is to load one on the drive and attempt a copy again. You can waste a lot of time that way. 'Aren't there some sort of standards for these things?' you wonder. Well, there are, but unfortunately, they are too flexible. Chuck Doty, technical service specialist at 3M Company said there is an agreed-upon, standard length for computer tapes.

The American National Standards Institute (ANSI) provides one. But the main cause of inconsistent length is the inexactness of this ANSI standard. ANSI specifies that the distance from the end-of-tape marker to the physical end of the tape must be between 25 and 30 feet. When you add this to other variable factors, such as the block size of your data and the number of write-skips that occur, the range of your tape's working length can vary from 2,352 to 2,411 feet - a 59-foot difference.

'Tape made in accordance with ANSI standards will be about 2,372 feet between markers, but that will vary from manufacturer to manufacturer and from day to day,' Doty said. 'Most of the specs that I've seen from different manufacturers are based on ANSI specs,' said Dave Lubert, a technical services engineer at Verbatim. 'We look at the distance between markers as being 2,370 feet, plus or minus 5 feet,' he said.

'2,406 feet (plus or minus 2) between markers,' said BASF's product manager for computer tape, Ken Brown. '3M has tape available on special order that is 2,400 feet (minimum) between markers,' said Doty. Until standards are more stringent, tape length will continue to be unpredictable. GET BRANDED What's more maddening than to get most of a tape copied, then run across a series of write-skips and have the drive reject the tape?

Finding quality tape is a task of trial and error among brands and the products they produce. BASF, for example, makes three grades of tape each more reliable than the next. But even they won't be perfect. 'Our upper two grades generally don't have errors. But tape is a wearing medium, so even a high quality tape that is initially free of write errors won't stay that way forever,' BASF's Brown said.

The best bet is to find a brand of tape you like and use it exclusively. That won't do away with problems completely. But, over time, it should keep your tape hassles to a minimum. (The Missouri Institute for Computer-Assisted Reporting uses 3M Black Watch No. 700 computer-tapes. This is after several misadventures with other brands of tape. Let us know if you have had any luck, good or bad, with other brands.) RETURN TO SENDER Write-skip errors can result from inconsistencies in the manufacturing process.

All tape is made of polyester film coated with a magnetic material on one side. The process starts with a polyester web a few feet wide. The webbing is coated, and then slit into half-inch widths. Inconsistencies in the formulation of the coating and its application to the webbing is one source of error. But the slicing can also be a problem. Doty said maintaining consistent width and a straight line when slicing tape while making sure no debris is generated can be difficult.

It's is a matter for plant maintenance, he said. If a tape is bad, call the manufacturer. The problem could have originated there. LIVE AND LET DIE Archive keepers, take note. In days of old, tape was tested to see if it would record 800 bits of data per inch, Verbatim's Lubert said. Today's drives are spewing out 6250 bits per inch and older tapes often can't accept data at that speed. If you have older tapes in your collection, perhaps it is time for a transfer.

In the meantime, store your tapes in a safe, cool, dustless place. How tapes are handled and stored before and after you get them, can have an impact on the way the they perform for you. Make sure your supplier is aware of this. Does your supplier store tape in an atmosphere hot enough to damage it? Is the dust in the vendor's storage area so thick that the fork-lift drivers have to navigate by radar?

If your vendor seems unable to supply you with inconsistent quality in the same brand of tape, you might look for another place to spend your money.