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 NOTICE: TO ALL NORTHGATE BRAND COMPUTER OWNERS


 RE: USING AN RLL CONTROLLER STANDARD ON A NON-RLL HARD DISK




      Recently I had the misfortune of having a hard disk failure on
 my Northgate AT machine, but fortunately, while it was still under
 warranty. As per Northgate's guarantee, they promptly shipped me a
 new hard disk along with complete installation instructions. 

      The disk that failed was a Miniscribe #3675 drive. However,
 the replacement disk I received from Northgate was a Miniscribe
 #3650. After a call to Northgate's tech department I was assured
 that the #3650 drive was indeed the correct replacement for the
 #3675 drive, and that they were really the same drive. 

      Not being born yesterday and wondering why Miniscribe would
 have two numbers for one drive, I decided to call Miniscribe in
 Longmont, Colorado, and guess what they said - they are not the
 same drive. The #3675 is certified for RLL (run length limited)
 encoding and the #3650 is not. The #3650 is certified for MFM
 (modified frequency modulation) encoding only.  

      As most Northgate computer owners know, under the ST-506/412
 hard disk controller interface standard, Northgate uses only the
 RLL encoding scheme on their hard disks for the storage of data .
 The difference between RLL and MFM is that MFM (the oldest and most
 widely used encoding method) uses 17 sectors per hard disk track
 and transfers 5 megabits-per-second of information, while RLL uses
 26 sectors per hard disk track with a 7.5 megabit-per-second
 transfer rate. This gives the RLL encoding scheme a 50% increase in
 storage capacity over MFM encoding. 

      PC Magazine (May 16, 1989 p.270) states that in order to take
 advantage of the RLL encoding method - "You also need a disk drive
 that has tighter mechanical tolerances than are required for
 conventional MFM, and one whose electronics have the bandwidth to
 handle the RLL data". "Don't just trust that an MFM drive from a
 reputable manufacturer will meet the more stringent RLL
 requirements." "If you're going to use an RLL controller, make sure
 the drive you intend to use is certified for RLL operation". It
 goes on to say that - "Many users, and even a few manufacturers [I
 think they mean Northgate], have tried this [using an RLL disk
 controller on an MFM hard disk], and the results - often a
 complete, irrecoverable loss of all data 6 months down the line-".

      The tech department at Miniscribe told me that Northgate was
 buying their #3650 hard disk drives and using them with RLL
 controllers against the recommendations of Miniscribes engineering
 department. In fact, Miniscribe says they are not honoring ANY
 warranty on these disks at all. But Northgate says they will
 warrant them for one year, and they disagree with Miniscribe's
 engineers. 

      Guess whose engineers I'd believe?
     

      I expect most computer owners would want their hard disks to
 last more than one year. And clearly, from what I can find out,
 sticking a RLL controller card on an MFM hard disk would compromise
 the data integrity and possibly even the life expectancy of the drive
 itself. In my opinion, Northgate has substituted a substandard hard
 disk in this configuration.  

      At first I thought they were only distributing MFM drives as
 replacements for defective drives, until I talked with a Northgate
 official, who informed me they had installed the #3650 drive in
 over 5000 new computer systems.

      It's my understanding now that Miniscribe is discontinuing the
 #3675 drive, although I haven't verified that.

      After I realized what Northgate was attempting to do with my
 system, I complained to their customer satisfaction department. I
 told them I was shipping their #3650 disk back and I would only
 accept a Microscience brand #1060 replacement (this is certified
 for RLL by the manufacturer). After some haggling, they agreed to
 supply me with the Micro Science RLL certified disk.  

      If any Northgate owners are interested in reading more
 information on this subject, PC Magazine, May 16, 1989, p263-275
 and PC Magazine, June 27, 1989, p95-100 are excellent sources to
 consult. 

      And for those owners who are interested in checking their
 Miniscribe disk to see if it is the #3650 or #3675, I will explain
 where the OEM sticker can be found. However, I have to issue this
 WARNING!

                           WARNING!!!!!

      Serious damage can result to your computer from static
 electricity. If you intend to remove the computer cover, please be
 aware of the precautions needed to avoid damage, some of which I
 will list, but if you do not have experience doing this, please
 take your system to computer store and have them check it for you.
 I will not be responsible for any damage you do to your system. The
 following points are just some of the precautions you need to be
 aware of and they do not represent the complete precautionary
 environment. 

     
      1.Your system should be unplugged and put on a non-metallic
 surface that gives you easy access to the rear of the unit. 
      2. Remove the screws on your particular type case and SLOWLY
 slide the cover forward being careful not to hook any cables.
      3. DO NOT touch any chips or circuit boards or components -
 even the smallest amount of static electricity can destroy your
 electronics. 
      4. In Northgates standard size AT case, the hard drive will be
 the gold colored drive in the middle slot of the internal bays.
      5. Viewing your system from the rear, you should be able to see
 the curved rear portion of the hard drive. If controller card
 cables are in the way, use a non-metallic stick to move them gently
 far enough aside to see the rear of the hard drive (be very
 careful).



      6. The Miniscribe label is bright chrome with black letters
 and is located on the center vertical portion of the drives curved
 rear.
      7. Use a flashlight to read the label, if it is a Miniscribe
 disk it will have either 3650 or 3675 in the model number. 
      8. Don't pay any attention to labels that are white paper with
 dot matrix print - they are Northgate's labels. 
      9. Reassemble your unit.

     If you have a #3650 drive and you still have the picking
ticket from your original order, you might want to verify that the
controller card is indeed an RLL card. At this point what you do
with this information is up to you, but I suggest you first read the 2
PC Magazine articles I mentioned above  



                               Greg Angsten
                               P.O. Box 246
                               Crystal Lake, Ill
                                           60014
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