coleman@uxe.cso.uiuc.edu (08/24/89)
/* Written 9:13 am Aug 23, 1989 by bill@bilver.UUCP in uxe.cso.uiuc.edu:comp.sys.ibm.pc */ /* ---------- "Re: Low Density Disks in High Densi" ---------- */ >>This raises yet another question: I have a 1.2M 5-1/4" drive in my AT clone. >>It is able to read/write low density 360K diskettes (using the 360K format) >>with no problems, and I swap 360K diskettes with my XT clone all the time >>with no problems. How does the 1.2M drive know to change its write current >>in order to successfully write a 360K floppy? >That's simple. Part of the formatting routine. You format HD and it goes to >the higher current. DD and it uses the lower. If the disks had been made >different for hd/dd the problems might not exist. /* End of text from uxe.cso.uiuc.edu:comp.sys.ibm.pc */ That doesn't explain why I am able to successfully read/write 360K diskettes FORMATTED WITH A 360K DRIVE in my 1.2M drive! How does the 1.2M drive know not to use high write current when writing data to a 360K disk? Scott kubla@uiuc.edu
hiebert@mdivax1.uucp (Graeme Hiebert) (08/26/89)
In article <45900267@uxe.cso.uiuc.edu> coleman@uxe.cso.uiuc.edu writes: > > /* Written 9:13 am Aug 23, 1989 by bill@bilver.UUCP in uxe.cso.uiuc.edu:comp.sys.ibm.pc */ > /* ---------- "Re: Low Density Disks in High Densi" ---------- */ > >>This raises yet another question: I have a 1.2M 5-1/4" drive in my AT clone. > >>It is able to read/write low density 360K diskettes (using the 360K format) > >>with no problems, and I swap 360K diskettes with my XT clone all the time > >>with no problems. How does the 1.2M drive know to change its write current > >>in order to successfully write a 360K floppy? > > >That's simple. Part of the formatting routine. You format HD and it goes to > >the higher current. DD and it uses the lower. If the disks had been made > >different for hd/dd the problems might not exist. > /* End of text from uxe.cso.uiuc.edu:comp.sys.ibm.pc */ > > That doesn't explain why I am able to successfully read/write 360K diskettes > FORMATTED WITH A 360K DRIVE in my 1.2M drive! How does the 1.2M drive know not > to use high write current when writing data to a 360K disk? > > Scott > kubla@uiuc.edu I am not the most experienced PC user (indeed, I only used them at a previous job for 8 months), but it sounds like it would be pretty simple to me. If the disk requires a high current write, it could specify it somewhere on the disk when it is formatted. When it writes data to the disk, it merely has to first read enough of it to find out what current it has to use. Since the 360K disks will not say "use high current," the drive uses low current for those disks. Easy, peasy, double-squeezy (as my grade 6 teacher used to say). -g -- Graeme E. Hiebert | So many of us seek pleasures to acquire hiebert@mdivax1.uucp | happiness, yet so few of us are happy ...!ubc-cs!van-bc!mdivax1!hiebert | with the pleasures we find. ---------------------------------------------------------------------------
rlb@cs.odu.edu (Robert L. Bailey) (08/26/89)
In article <45900267@uxe.cso.uiuc.edu> coleman@uxe.cso.uiuc.edu writes: > >/* Written 9:13 am Aug 23, 1989 by bill@bilver.UUCP in uxe.cso.uiuc.edu:comp.sys.ibm.pc */ >/* ---------- "Re: Low Density Disks in High Densi" ---------- */ >>>This raises yet another question: I have a 1.2M 5-1/4" drive in my AT clone. >>>It is able to read/write low density 360K diskettes (using the 360K format) >>>with no problems, and I swap 360K diskettes with my XT clone all the time >>>with no problems. How does the 1.2M drive know to change its write current >>>in order to successfully write a 360K floppy? > >>That's simple. Part of the formatting routine. You format HD and it goes to >>the higher current. DD and it uses the lower. If the disks had been made >>different for hd/dd the problems might not exist. >/* End of text from uxe.cso.uiuc.edu:comp.sys.ibm.pc */ > >That doesn't explain why I am able to successfully read/write 360K diskettes >FORMATTED WITH A 360K DRIVE in my 1.2M drive! How does the 1.2M drive know not >to use high write current when writing data to a 360K disk? Simple. When DOS logs in a new disk for the first time, it reads track 0. It then steps in 1 track and reads again. If it is a high density drive with a 360K disk, the track number will still be 0. If it is a HD drive with a 1.2M disk the track number will be 1. This difference occurs because the 360K tracks are roughly twice the size of the 1.2M tracks. When it has been determined that the disk is a 360K, the drive is forced to write at the lower current level. It also double steps the drive to position the head over the proper track. This is because in a HD drive track 1 is twice as far from track 0 as it is for a 1.2M diskette. Hope this clears up the confusion. Bob Bailey
sac90286@uxa.cso.uiuc.edu (Kubla Khan) (08/28/89)
In article <9828@xanth.cs.odu.edu> rlb@cs.odu.edu (Robert L. Bailey) writes: >>That doesn't explain why I am able to successfully read/write 360K diskettes >>FORMATTED WITH A 360K DRIVE in my 1.2M drive! How does the 1.2M drive know not >>to use high write current when writing data to a 360K disk? > >Simple. When DOS logs in a new disk for the first time, it reads track 0. >It then steps in 1 track and reads again. If it is a high density drive >with a 360K disk, the track number will still be 0. If it is a HD drive >with a 1.2M disk the track number will be 1. > >Hope this clears up the confusion. It certainly does, Bob; Thanks! With that explanation, it's also clear why a disk formatted on a 360K drive and written to by a 1.2M will often be readable on a 360K drive, whereas a 360K disk formatted by a 1.2M drive to the low density format is often unreadable on low density drives - the 360K drives have trouble accurately tracking the narrower tracks written by the HD drive. Right? Scott kubla@uiuc.edu
mdfreed@ziebmef.mef.org (Mark Freedman) (08/29/89)
(how does the 1.2 meg drive recognize a diskette formatted as 360K)
The FAT contains a media-descriptor byte, which contains a code representing
the diskette format. In your case, a 1.2 meg is F9, while a 360K is FD.
KDM101@PSUVM.BITNET (Kevin Maher) (09/01/89)
The way a 1.2M drive works to squeeze that data on, is to change the disk
rotation speed and to double the number of tracks to 80. If you pay attention,
you should notice that a 1.2M drive will take slightly longer to begin reading
a disk when you have changed formats. This however, is not how a HD 3.5"
drive works. (1.44M) A standard 720K 3.5" drive has 80 tracks with 9 sectors
per track, while the 1.44M still has 80 tracks, but has 18 sectors per track.
-------------------------------------------------------------------------------
Kevin Maher - Pennsylvania State University - The Behrend College
Computer Center technical assistant
KDM101@PSUVM.BITNET PSUVM.PSU.EDU
-------------------------------------------------------------------------------wcf@psuhcx.psu.edu (Bill Fenner) (09/04/89)
In article <5190040@hplsla.HP.COM> janh@hplsla.HP.COM (Jan Hofland) writes: | |With all due respect, the rotational speed of the drive doesn't |change. The write frequency, on the other hand, is doubled so the |the number of sectors per track doubles. With all due respect, the rotational speed of the drive, for 5 1/4" 1.2mb disks, does change. So does the write frequency. The rotational speed for a high desnsity 5.25" disk is 360rpm, as opposed to 300rpm for a 360k disk. Bill -- Bitnet: wcf@psuhcx.bitnet Bill Fenner | aaaaaaaaa Internet: wcf@hcx.psu.edu | r UUCP: {gatech,rutgers}!psuvax1!psuhcx!wcf | g Fido: Sysop at 1:129/87 (814/238 9633) \hogbbs!wcf | h