Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!news.larc.nasa.gov!ipsun.larc.nasa.gov!jcburt From: jcburt@ipsun.larc.nasa.gov (John Burton) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Can I Low Level Format my MFM drive with 17 < SECTORS < 26 ? Message-ID: <1991Mar19.135057.2372@news.larc.nasa.gov> Date: 19 Mar 91 13:50:57 GMT References: <5832@trantor.harris-atd.com> <1991Mar16.022315.28142@digi.lonestar.org> <5855@trantor.harris-atd.com> Sender: news@news.larc.nasa.gov (USENET Network News) Organization: NASA Langley Research Center, Hampton, VA USA Lines: 94 In article <5855@trantor.harris-atd.com> sonny@trantor.harris-atd.com (Bob Davis) writes: >In article <1991Mar16.022315.28142@digi.lonestar.org> kgallagh@digi.lonestar.org (Kevin Gallagher) writes: >>In article <5832@trantor.harris-atd.com> sonny@trantor.harris-atd.com (Bob Davis) writes: >>> >>> I know that MFM normally uses 17 Sectors/Track and RLL uses >>>26 Sectors/Track. But is there a fundamental reason I cannot low >>>level format my MFM drive to 20 Sectors/Track, say, in an attempt >>>to increase drive capacity? Does the MFM controller FORCE the >>>use of 17 S/T and the RLL controller 26 S/T or might they do whatever >>>they are told by the Low Level Formatter program? >> >>Without going into the technical details, the answer to your first question is >>yes. Given the fixed RPM of your drive, the MFM encoding technique, and the >>speed at which the drive firmware writes to the disk, there is room for only >>17 sectors/track. If you try to write an 18th sector on a track, you risk >>having part of the 18th sector overwrite part of the 1st sector. >> > > But I can take an MFM drive and RLL it to 26 sectors/track and there >is no problem with getting done with all 26 tracks in one revolution of >the platter. >Seems to me that the disk formatting routines in the BIOS must always know >how fast to write sector-definition info to the disk in order to complete >the specified number of sectors in exactly one revolution of the fixed >speed disk. Don't the BIOS routines do that? > > Some Low Level Formatting programs (such as Western Digital's WDFMT >program) allow the user to simply enter Cylinders, Heads, Sectors, and >all that other stuff and then it goes away and does its thing. Do such >programs do the right thing if you tell it to low level your MFM drive >using 18 sectors instead of 17? > > It simply occurs to me that MFM drives are designed to normally carry >a data density that corresponds to 17 sectors, but that some of the drives >are probably better than others and the platters might be of high enough >quality to carry 18 sectors, some 19, some even higher. > > My question is: Do the MFM controllers enforce the 17 sector choice >or might I use higher values? Do RLL controllers enforce the 26 sector choice? > > I realize that, even if possible, the choice of higher numbers would >stress the capability of the platters and that generally data would be at >a higher risk. Generally. In specific cases with better than average >drives, things might be OK...Just as some drives will RLL and some wont. > > I guess I will play with this on a drive soon and see what happens. > > >_____________________________________________________________________________ >Bob Davis, UofALA alum \\ INTERNET: sonny@trantor.harris-atd.com | _ _ | >Harris Corporation, ESS \\ UUCP: ...!uunet!x102a!trantor!sonny |_| |_| | | >Advanced Technology Dept.\\ AETHER: K4VNO |==============|_/\/\/\|_| >PO Box 37, MS 3A/1912 \\ VOICE: (407) 727-5886 | I SPEAK ONLY | |_| |_| | >Melbourne, FL 32902 \\ FAX: (407) 729-3363 | FOR MYSELF. |_________| You could try reading what Kevin wrote. There is a BIG difference between an RLL controller and an MFM controller. BOTH will work on the same disk (some of the time anyway, depending on the quality of drive and the head positioning mechanism - voice coil will generally work both ways, stepper motor will give you problems). Basically what the controller does is establishes what fraction of a revolution is considered a sector. In the case of an MFM controller thats 1/17 th of a revolution (actually a little less, but thats not important here) when reading/writing a sector, the controller tells the r/w heads to get in position and read/write for a specific period of time. that period of time is determined by the number of sectors per cylinder and the platter rpm. An MFM is designed for 17 sectors, an RLL designed for 26. If you use the low level formatting program that is installed in BIOS on some controllers, you find you don't have a choice of how many sectors per cylinder. The only reason that the LL formating programs you can buy (Ontrack's Disk Manager, Western Digital's WDFMT, etc) have the option of specifying sectors per track is to distinguish what kind of controller you have installed (MFM = 17, RLL = 26 or 27, ESDI = 34). The sector option is NOT there so that you can arbitrarily specify whatever value you want. If you could get more storage out of a disk that way, don't you think that there would be several software products on the market to do just that? At best, your controller will be smart enough to ignore what you tell it and format the disk the way it SHOULD be formatted. At worst you'll muck up your controller AND your disk to a point that neither is usable. If you want to get more space out of your MFM disk try using an RLL controller, but ONLY if: 1) the disk has a voice coil head actuator mechanism, 2) the disk has a thin film (sputtered-platted) media, NOT the standard oxide-coated media, 3) use short cables with gold plated connectors. Basically if its a high quality drive by CDC (Imprimis), Maxtor, Priam, Micropolis, or Mitsubishi you stand a fairly good chance of reliably increasing your drives capacity by ~50%. If your drive is the average inexpensive Seagate drive, don't bother... You can generally tell if your drive has a stepper motor or voice coil actuator by the number of heads, and the auto park feature...voice coil will generally have an odd number of r/w heads and have poweroff auto-parking heads, stepper motors will generally have an even number of heads and not have poweroff auto-parking...auto-parking requires additional circuitry on the stepper motor models, but not on the voice coil models... John Burton G & A Technical Software (gatsibm.larc.nasa.gov)