sonny@charybdis.harris-atd.com (Bob Davis) (03/15/91)
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? Thanks. _____________________________________________________________________________ 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. |_________|
kgallagh@digi.lonestar.org (Kevin Gallagher) (03/16/91)
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. If you slowed the RPM of the drive down, and you told the controller to write more than 17 sectors per track, you would be able to write more sectors on a single track; but the hardware might have trouble reading what your wrote, especially on the innermost tracks. -- ---------------------------------------------------------------------------- Kevin Gallagher kgallagh@digi.lonestar.org OR ...!uunet!digi!kgallagh DSC Communications Corporation Addr: MS 152, 1000 Coit Rd, Plano, TX 75075 ----------------------------------------------------------------------------
sonny@charybdis.harris-atd.com (Bob Davis) (03/19/91)
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. |_________|
jcburt@ipsun.larc.nasa.gov (John Burton) (03/19/91)
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)
kgallagh@digi.lonestar.org (Kevin Gallagher) (03/20/91)
In article <5855@trantor.harris-atd.com> sonny@trantor.harris-atd.com (Bob Davis) writes: > 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. That's because MFM encoding of a sector takes up more time and space than RLL encoding. The platters in the drive spin at the same speed regardless of how you format the drive. The nature of RLL encoding places greater demands upon the drive hardware. However, it turns out that the quality of a large number of drives manufactured and sold as MFM drives are of the quality that then can reliably read and write RLL encoded data. The specs needed to reliably read RLL encoded data are somewhat more demanding than those needed to read MFM encoded data. There are plenty of similar examples in the floppy disk world. In the early days of the Apple II computer, the first Apple drives had 13 sectors per track. Later on, Apple realized that the drive could reliably read data written to disk with a more economical encoding scheme which would permit 16 sectors per track. All then needed to do was modify the controller to deal with the new encoding. IBM first came out with floppies with 8 sectors per track and later upgraded to 9 sectors per track on 5.25 inch drives. And so on. Thus, unless you slow down the fixed speed of the drive, there is not enough room on a track to fit more than 17 MFM sectors per track. But slowing down the speed of the drive runs the risk that the hardware will not be able to read what you write, especially on the shorter length inside tracks. -- ---------------------------------------------------------------------------- Kevin Gallagher kgallagh@digi.lonestar.org OR ...!uunet!digi!kgallagh DSC Communications Corporation Addr: MS 152, 1000 Coit Rd, Plano, TX 75075 ----------------------------------------------------------------------------
gp310ad@prism.gatech.EDU (ROBERT DUCKWORTH) (03/20/91)
Just to add some wood to the fire. The 17 sector/track assumes 512 byte
sectors. If you make them smaller, you can have more. For instance, I
have ESDI drives with 128 byte sectors. Can't get 4 times as many as the 512 byte, but it's close.
;-)
Bob
--
Bob Duckworth -everything you know is wrong-
Earth & Atmospheric Sciences, Georgia Tech, Atlanta, 30332
uucp: ...!{allegra,amdmhplabs,ut-ngp}!gatech!prism!gp310ad
Internet: gp310ad@prism.gatech.edu 404-894-3890(o) 874-5051(h) 313-0095(m) norcott@databs.enet.dec.com (Bill Norcott) (03/20/91)
In article <1991Mar19.185406.29567@digi.lonestar.org>, kgallagh@digi.lonestar.org (Kevin Gallagher) writes... >In article <5855@trantor.harris-atd.com> sonny@trantor.harris-atd.com (Bob Davis) writes: >> 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. > Why dont you sell the MFM and get a SCSI drive with maybe 32-50 sectors per track! (or ESDI). This will *really* increase your throughput and the cost may be less than you think. I have been seeing the 105MB Quantums for less than $350 mail order. Bill Norcott
martin@saturn.uucp (Martin J. Schedlbauer) (03/20/91)
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? > I have in the past formatted a Maxtor XT1085, which is a 17 sector/track MFM hard disk, to 18 sectors/track. I tried more but the low-level format failed at higher than 18 settings. It'll work, but chances are very high that your harddisk controller BIOS can't handle anything but 17 sectors/track. That typically means that the track buffer only holds 17 sectors worth of data. For a 1:1 interleave that means one revolution to read one track. If you increase the drive capacity to 18 sectors per track you'll read 17 + 1, i.e. an extra revolution is needed to read a single track. Ergo, your read times increase almost two-fold. Of course, at 18 or more sec/track, you mau experience media failure soon... ...Martin -- ============================================================================== Martin J. Schedlbauer | martin@saturn.UUCP | ...!ulowell!saturn!martin 8 Gilman Road | mschedlb@ulowell.edu | ...!uunet!wang!saturn!martin Billerica, MA 01862 USA | CIS: 76675, 3364 | /\/\/\/\/\/\/\/\/\/\/\/\/\/\
wjb@cogsci (03/21/91)
[Lots of people talk about why you can/can't format more then 17 sectors with an MFM controller, 26 with RLL etc.] My answer is: I don't think so. One thing which might help, is to remember that the controller clocks the data signal to the drive at a fixed rate (at least during formatting) based on a crystal on the board. This means that depending on the clock rate of the crystal and the RPM of the drive, there are just so many bits (magnetic flux changes) that can be written by that controller on a single track. Some of those bits are used by headers, trailers, and error correction codes. You might be able to increase the capacity of your system by increasing the clock rate. This would require that the rest of the electronics on the controller and the drive could handle the faster state changes. I've been told that some drives have lowpass filters which would actually filter out any signals which changed at a faster rate then that for which they are designed. If it did work, you could then try format the drive with more sectors. Another interesting note is that each flux? time does not actually store a data bit. Bits are encoded and actually take up more then one flux time. I think the big difference between MFM and RLL is that the encoding scheme is more efficient (i.e. has a smaller expansion ratio). I think this expansion is used by the hardware to help recover the clocking/phase of the data signal when the data is being read back from the drive. This allows for small variations in the RPM of the drive not to affect the ability of the controller to reread the data. Perstor(?) sells controllers which store even more data then MFM or RLL controllers on the same drives. Does anybody know what methods they use to increase capacity? Is it just better encoding or do they actually increase the rate of magnetic flux change? Bill Bogstad P.S. All of the above is by an intelligent laymen. I think the general theory is correct, but some of it is probably wrong. Hopefully a real EE or CE will correct me. I became a programmer a long time ago. :-)
sigma@jec302.its.rpi.edu (Kevin J Martin) (03/21/91)
kgallagh@digi.lonestar.org (Kevin Gallagher) writes: >IBM first came out with floppies with 8 sectors per track and later >upgraded to 9 sectors per track on 5.25 inch drives. Just to nitpick, that modification was made by DOS 2.0 with NO HARDWARE CHANGES. You could format 180K on single-sided 5.25" disks - the original drives that came with IBM-PCs. The difference was that DOS 2.0 installed a different drive parameter block, specifying smaller gaps between sectors (and improved timing parameters, too) and other technical details. Such an approach isn't available with hard drives, however - the hardware definitely handles the high-speed data encoding needed. -- Kevin Martin sigma@rpi.edu
sonny@charybdis.harris-atd.com (Bob Davis) (03/22/91)
In article <1991Mar19.135057.2372@news.larc.nasa.gov> jcburt@ipsun.larc.nasa.gov (John Burton) writes: >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? >>> [DELETIONS] > >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 SIR: I *did* read what he wrote. Of course there is a big difference between MFM and RLL. But he did not say whether or not the controllers enforced the 17 sector value for MFM and the 26 for RLL. And there is absolutely no reason why anyone MUST assume, a priori, that MFM forces 17 sectors, or that RLL forces 26. One LEARNS that. [DELETIONS] > 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? I make it an ABSOLUTELY INFLEXIBLE RULE NEVER TO *ASSUME* THAT AN "OBVIOUS" THING HAS ALREADY BEEN THOUGHT OF -- ALWAYS. Don't you? > >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... > YES. GENERALLY. But as with all GENERAL assertions, there are exceptions, and I am not averse to taking the exceptions if they present themselves. For example, I have had a CHEAP Miniscribe 3425 MFM 20 Meg hard drive in FLAWLESS 32 Meg RLL service for TWO years now. > >John Burton >G & A Technical Software >(gatsibm.larc.nasa.gov) Bob Davis _____________________________________________________________________________ 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. |_________|