Part V: The Deadly "Bad Disk Block"
by John Burns
Ever had disks that suddenly just won't work?. It can drive you crazy. This article might save you a lot of grief.
I've had my ADAM for five years and the ADAM Disk Drive (DD) for about two years. It was a salvage unit that I picked up fairly cheaply ($150) but I have had very good, dependable, yeoman service from it. Recently, however, I began to notice that I was running into an increasing number of disks that would come up with the error message "CANNOT READ TO THIS FILE" or "CANNOT ACCESS THIS FILE". And, even worse, a lot of disks that would show "BAD BLOCK ON THIS DISK" when formatted.
For those who do not know how disks and the ADAM system works, a little background might help. When disks are bought, they are usually labelled as 5 1/4 inch, Double Sided, Double Density Disks. They usually have only one small, square notch on the edge. When new, they can be used in any machine (IBM, Commodore, ADAM, etc.,) just like audio cassette tapes can be used in any tape recorder. However, just as audio cassette tapes require modification before ADAM can accept and read them, so do the disks.
FORMATTING TAPES vs. DISKS:
In cassette tapes, two locating holes must be drilled in the upper corners of the casing and then the tape must be formatted. This process enters the READ / WRITE instructions and inserts the DIRECTORY template. A tape user has real problems doing the formatting of blank tapes unless he has proper Data Drive Cassettes, multiple drives and access to something like the MEGACOPY program. Likewise, the disks must be formatted before ADAM will accept them, but it's much easier.
The formatting procedure is contained directly on the Operating System disk called DISK MANAGER that comes with your ADAM DD. Your ADAM DD is a single-sided drive that reads only on one side of a disk. It can be upgraded to a DOUBLE SIDED drive by several agencies, including ADAM'S HOUSE. To format a disk, you load the DISK MANAGER program, just as you would load SmartBASIC. The screen commands for DISK MANAGER permit you to format the new disk. You are asked if you wish the new disk to be a duplicate OPERATING SYSTEM disk or just a DATA disk. If you only want word processing storage, you don't need the operating system included, but, if you plan on using the disk(s) for standalone program storage, then you should enter the operating system. It's as simple as inserting the new disk in the drive and waiting until it shows the proper directory.
(No!, you can't use DISK MANAGER to format datapacks!) When you format you are given a second option besides SYSTEM or DATA. You are asked if you wish to have the disk checked for BAD BLOCKS. This is a method of the machine doing a trial READ on all of the new disk to make sure there are no breaks in the magnetic coating and that the factory universal coding instructions are all there. If you do not request Bad Block checking, the machine will insert the directory in about two minutes. With Bad Block checking, formatting time is almost doubled to about three and a half minutes. (this can be reduced with a Fast Read EPROM chip but that's another story.) It is HIGHLY RECOMMENDED that you check for Bad Blocks. If you do not, you will have files and documents that appear to record properly but will refuse to come back up out of memory. Instead you will get the error message "CANNOT READ THIS FILE", or sometimes, "BAD BLOCK ON THIS DISK". Whatever you recorded is likely gone forever.
There are, however, occasions when you have properly formatted a disk, have checked for Bad Blocks and yet you suddenly start to get the error messages. There are a number of causes, only some of which are curable. Every disk envelope has the standard cautions against abuse. If you bend the disk, expose it to a magnet (Don't put disks or tapes on top of your monitor!), touch the exposed mylar surface of the disk with your oily fingers, or allow the disk to be exposed to temperatures in excess of 52 degrees C (125 degrees F), t will read erratically or not at all. The one item everybody forgets is the heat caution. You say, "WHAT HEAT"?". If you have operated your disk drive too long with frequent saving of information, and you haven't paid particular attention to artificial cooling, you may cook your disk. Hard working DD's get HOT and a hot disk won't read properly. (The same thing applies to hot datapacks!) Feel the top of your datadrive or disk drive after a hard working session. Sometimes it will almost burn your hand. DON'T BLOCK THE VENTS with papers or use it as a reading stand for your favourite programmer's book. To increase efficiency of your drive, get a small blower or fan to circulate the air through the vents.
Another item that causes difficulties is the failure to regularly
clean the reading head and the gripper drive of your DD. The
head gets dirty, just like a cassette recording head. Worse,
the circular drive sections on disks get dirty and oily from
handling and then transfer skin oil to the internal disk gripper.
The result is a grinding noise when you attempt to load disks.
This indicates that the disk is slipping and not coming up to
proper speed in the drive. To solve it, first get a good Drive
Cleaning Disk Kit and the proper alcohol solvent. The kits cost
about $7.00 (CDN). If you do a lot of work on your computer,
you should clean at least once a month. All you have to do is
put the cleaning solvent on the disk, insert it in the drive,
and turn the power off and on to get the disk to intake. Let
it spin for about 30 seconds and the job is done. But, many users
forget to include solvent on the centre drive
LAST DITCH SWABBING:
If you have a critical disk that keeps skidding and not reading, even after running in the cleaner disk, it is time for more positive action. Take alcohol solvent on a Q-Tip and GENTLY swab the drive ring in the centre of your disk. BE CAREFUL! Too hard and you will scratch the Directory Section and then the disk is really gone. I suggest that if you have to go this far, and you do get the directory and files up, immediately transfer your information to a fresh disk. It is likely the disk you had to swab won't last long and you may not get all the files up again. Get it while the getting is good and make a BAK (Back Up Copy.).
EXPERIENCE THE HARD WAY:
As mentioned at the start of this article, I recently started
getting a lot of Read / Write error messages. I had done regular
cleaning of the head but I forgot to clean the gripper circle.
When I cleaned it, a lot of previously unreadable "bad"
disks suddenly came back on line. However, I noticed I had one
particular brand of disk that were consistently failing, even
after head cleaning and swabbing of the drive circles. These
disks were FUTURE DISCOUNT SUPERSTORE house brand disks and were
only a month old. I had properly formatted and checked for bad
blocks and had protected them, but, no matter what I did, I was
still getting failures. In some cases, it was only the failure
to record and recover document files. I would get the directory
but not the file. The error message would read, "CANNOT
READ THIS FILE". I did everything I could but was left with
no option but to retype my file. When it happened again, I went
for complete reformatting. Lo and
On some others, I could not even get the directory up, only the error message, "CANNOT ACCESS THIS FILE". In one case, 1 was in the middle of a document and tried to save it. Up came the error message and nothing I could do would give me re-entry to the disk. No Deal. All I got was the message "I/O (Input/Output) Error". I tried entry with the DISK MANAGER program and got the order to insert a formatted disk. I tried to reformat but could not even do that.
It took a while but I think I have discovered the cause. In a word, CHEAP! I had bought cheap, discount, no-name disks and they had failed. Inspection with a magnifying glass showed that the magnetic coating on the mylar at the gripper circle had worn off. The bottom side of the showed unusual tracking in the center gripper section. It appears that the coating just plain wore off.
I WANT MY MONEY BACK:
Out of the 10 disks in the Future Superstore house brand package, I have now had major failures on 7 of them. That's just too darned risky to use. I don't know if I just got a bad batch or if all of them are like this. In any event, the box says they have a "Limited Error Free Warranty" (Whose life? Mine or the disks?) With my luck, the warranty means it's lifetime is up when it stops working. MORAL OF THE STORY? Keep the drive cool, clean regularly, protect the disks from finger oil, and, above all, BUY GOOD DISKS!
If all the maintenance and protection of your disks still result in failures, you may have a problem with the calibration of your drive, I am told by a fellow who was a service manager for DISC (Dale Integrated Services Co., the forerunner of National Electronics Co., in Scarborough) that the drives will occasionally go out of balance and have to be recalibrated. Apparently, this requires special programs and the use of an oscilloscope and is definitely not a home repair, or cheap. National has a basic service charge of about $50. I think if mine went off line, I'd just send the whole thing to ADAM'S HOUSE and have it replaced with the double-sided kit.
Good ADAMing until next time.
c/o Richard Clee
Box 165, 260 Adelaide Ave. St. E.
Toronto, Ontario, Canada M5A 1N0