streeter@ingr.UUCP (04/08/86)
I have an Amiga which I purchased last November. I purchased the external disk drive at the same time. My drives make a noise when in use which has been described by several hardware-type friends as the result of a slow step-rate. I am told that the step-rate is controlled by software, and that the noise is the heads being jerked around, starting and stopping all the time. A correct step rate, they tell me, keeps the heads in constant motion during use. I am also told that there is nothing wrong with a slow step rate, but that I might see a minor disk i/o speed improvement with the correct rate. I obviously do not know what I am talking about, but what I understand from all this is that I might be able to make the software run my disks a little quieter, if someone who knows how would volunteer the information. An interesting point in all this is that newer drives do not make this noise, running the same software. This means either that the problem is not software, or the step-rate correctly matches the newer drives. I have suspected for some time that the vendor or model of the drives changed after my machine was shipped, but the store will not let me open one to see. Would someone (C= maybe?) comment on this? Can I change the step rate? Do I need to? Are newer drives different? Guy Streeter ...akgua!ingr!streeter
neil@amiga.UUCP (Neil Katin) (04/18/86)
In article <132@ingr.UUCP> streeter@ingr.UUCP writes: > I have an Amiga which I purchased last November. I purchased the external >disk drive at the same time. My drives make a noise when in use which has >been described by several hardware-type friends as the result of a slow >step-rate. I am told that the step-rate is controlled by software, and >that the noise is the heads being jerked around, starting and stopping all >the time. A correct step rate, they tell me, keeps the heads in constant >motion during use. I am also told that there is nothing wrong with a slow >step rate, but that I might see a minor disk i/o speed improvement with the >correct rate. > I obviously do not know what I am talking about, but what I understand >from all this is that I might be able to make the software run my disks a >little quieter, if someone who knows how would volunteer the information. > An interesting point in all this is that newer drives do not make this >noise, running the same software. This means either that the problem is not >software, or the step-rate correctly matches the newer drives. I have >suspected for some time that the vendor or model of the drives changed after >my machine was shipped, but the store will not let me open one to see. > Would someone (C= maybe?) comment on this? Can I change the step rate? >Do I need to? Are newer drives different? > >Guy Streeter >...akgua!ingr!streeter Alright. Here is the OFFICIAL WORD on step rates and disk drives. (by the way, ms -> milliseconds). The 1.1 release attempts to step at a rate of 3 ms per track. This is specified maximum step rate for all our drives. However, overhead in exec , the trackdisk device and the timer device make the actual step step rate more like 3.98 ms per track on a 68000 based amiga. I went through and tuned the 1.2 release, and got the overhead down by over 30% (e.g. the overhead is now ~540 microsecs). There is perhaps another 100 microseconds to be found, but they would be tough. Disk drives are mechanical things. Like all other mechanical things, they have "resonant frequencies". For our purposes, this means that certain step rates will result in constructive interference, also know as "disk grinding". Most 3.5" drives that I tested have a harmonic at 4.5 - 4.8 ms. The closer your step rate is to this value, the louder your disk will be. Over this value it gets quieter. This is actually a "feature" because older 5.25" drives had a step rate of 6 ms, and I'm sure someone worked hard to get the harmonic in between the two common rates (3 ms and 6 ms). Where does this leave our hero, the hacker-at-large? I can't comment on your drives, but mine doesn't sound different when stepped at 3.5 ms as opposed to (the maximum) 3.0 ms. The reason why I don't just subtract 1/2 ms from the requested time is that this time is all processor overhead -- the actual step rate on CSA's 68020 board is 3.34 ms. Better processors will be faster yet. What you can do (under 1.2) is set the step rate to whatever you want -- it is part of the newly defined "public" part of the disk unit structure. However, we can't support you if you make use of this feature. And I hope that only "users" actually change the value -- any application that changes the step rate will not be portable to faster machines. Anyway, I hope this clears things up. Neil Katin Commodore-Amiga Inc.