Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!usc!wuarchive!rice!uupsi!rodan.acs.syr.edu!amichiel From: amichiel@rodan.acs.syr.edu (Allen J Michielsen) Newsgroups: comp.sys.ibm.pc.misc Subject: Re: Drive Help Message-ID: <1990Dec11.194008.18580@rodan.acs.syr.edu> Date: 11 Dec 90 19:40:08 GMT References: <7065@plains.NoDak.edu> <90343.010956KDM101@psuvm.psu.edu> Sender: amichiel@rodan.acs.syr.edu Followup-To: amichiel@rodan.acs.syr.edu Organization: Syracuse University, Syracuse, NY Lines: 63 In article <90343.010956KDM101@psuvm.psu.edu> KDM101@psuvm.psu.edu >The resistor in question is called a terminating resistor. Now, as far as >I know, the resistor was only used on the original PC/XT systems. The >cable that connected the floppies was a simple straight ribbon. The resistor >was used to "tell" the controller that the drive with the resistor was the >A drive. (at least on a true IBM PC . the B drive is the first drive on the >cable and the A is the last) On the AT computer however, the floppy cable >was designed with a few wires twisted. This twist is what determined which >drive was A or B. I only quoted the entire section because virtually none of it was correct. Having missed the original posted article (I assume). Every pre-ps/2 floppy drive in a desktop class machine that came from IBM did have a terminating resistor pack. The whole function of this resistor is to properly terminate (end/kill) the signal at the end of the floppy controller cable. Whatever drive was at the end of the cable should have had the termination resistor. It is needed because of the physical limitations on the cables and input output gates of the electronics. Due to capacitive coupling, signals echo off the end of the cable and reflect back down the cable to the controller. This echo increases the noise on the line, causing data errors, decreased throughput, and lower reliability. The resistor pack is used for several reasons, first there are several methods of properly terminating the signals, and the correct size depends on the electronics involved, hence the drive manufacturers used a easily modifiable part. Selecting the drive number on the standard floppy system depends on several things. First, there is a built in cabling technique which allows 4 identically configured floppies (possibly except for termination technique, but independantly...) to be selected with ONLY a difference on the drive selection lines. The second technique would be to use a hardware address on the actual floppy drive to tell it, what drive number it actually it. Logically, you should configure a drive for drive 0 and then use the drive select lines to select the drives, else, use the drive X jumper and use the drive select 0 lines. However, IBM in their quest for new and better standards mixed both of these up. ALL IBM computers made by IBM use a twisted cable, and a drive selection of 2. Many clones (especially name clones, which generally are less true copies due to fear of law suits...) used a straight cable and then the drive selection jumpers of either 2 & 3 for a & b, or 2 & 1 for a & b, else 0 & 0 for a & b (implementing the intendard proposed floppy standard....), or even possibly 1 & 2 for a & b. The only way I can tell it to try it. There is a generally serious problem with improper termination... Virtually all new mixed &/or high density floppy controllers, and designed for soft termination on the floppy system. The older drives use hard termination. Most 3.5 drives now use soft termination, which is integral, and cannot be easily removed. Most dealers are not well educated (or informed or even care) enough to know that mixing hard termination with soft termination is a real problem. What happens, is that the bus drivers on the floppy controller are overheated and begin to fail when they get older. The result of this failure is that high density drives flip over into low density mode while writing high density disks, ruining the disk. They also may just begin writing garbage into a file, which creates a often unrecoverable data loss. Several things can be done, each indecreasing order... 1. dig into the soft terminated drives & rip out the terminating resistor pack. 2. move the drives so that the soft terminated drive is at the end of the physical cable -- making a new 'custom' cable if desired for keeping drive designations the same if desired... 3. remove the hard termination pack from the properly terminated drive, and either buy the proper size soft termination resistor pack, else forget the termination pack entirely. al -- Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu Bitnet: AMICHIEL@SUNRISE