6.5 Working with FDDs
Keep the following issues in mind when working with
FDDs:
- Choosing
-
3.5" HD FDDs are $15 commodity items made by several manufacturers.
We prefer the Teac FD235HF, but there is little difference between
brands. Buy whatever is offered. 5.25" FDDs are still available new
for $40 or so, but that won't last forever. If you
need a 5.25" FDD to rescue data on old disks, get the drive now. If
you patronize a local computer store, check there first. They may
have a stack of old 5.25" FDDs they'd be happy to
give away or sell cheaply.
- Installing
-
5.25" FDDs require a 5.25" half-height, externally accessible drive
bay. 3.5" FDDs can be installed in an externally accessible 3.5"
third-height bay, or, by using an adapter, in a 5.25" half-height
bay. The BIOS automatically detects installed FDDs, but can determine
type unambiguously only for 5.25" HD (1.2 MB) FDDs, which spin at 360
RPM rather than 300. For other drive types, older machines assume 360
KB or 720 KB and newer systems assume 1.44 MB. Use BIOS Setup to
confirm that the drive type is configured correctly.
- Cabling
-
If you add or replace an FDD, also replace the
cable,
particularly if it is the original cable. Manufacturers often fold
and crimp the FDD cable for improved cable routing and airflow. An
old cable that has been so treated is no longer reliable, especially
after you disturb it to install the new drive.
- Change Line Support
-
All but the oldest FDD controllers use line 34 for
Change
Line Support. When the FDD door is opened, the FDD signals on line 34
to tell the system that the diskette may have been changed. If you
install a 360 KB or 720 KB FDD, verify the Change Line setting,
ordinarily set on the drive by a jumper labeled
"Line 34" or
"Change Line." If you install such
a drive in a PC/XT-class system, leave the jumper open. On any later
system, install a jumper block to connect line 34 and enable Change
Line Support. Failing to do so and then writing to a diskette in that
drive may destroy the data on that diskette by overwriting the FATs
and root directory entries with data from the diskette that was
formerly in the drive.
- Cleaning
-
FDDs are used so little nowadays—an occasional boot or program
install—that head wear and media accumulation
isn't a problem. Dust needs to be removed
periodically. You can buy special FDD cleaning kits, but we
don't bother with them. Every few months (or when we
open the case for other reasons) we vacuum out the drive and drench
it down with Radio Shack Zero Residue cleaner or the equivalent.
- Repairing
-
Don't. Replace the drive. Modern 3.5" drives are so
cheap that it makes no sense to repair one, and they are often sealed
units without repair access anyway. Older 5.25" drives often are
repairable, but the cost to do so exceeds the cost of replacing the
drive.
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