chrisb@hubcap.clemson.edu (Chris Behrens) (11/01/90)
The subject says it all... But is there a way to utilize the full
2 meg, or is this taken up by the DOS formatting ??
Thank You.
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Chris Behrens
ChrisB @ {Hubcap||Gemini||Prism||Eureka||Clemson}.Clemson.Edu
Clemson University / Senior in Computer Science needs job !!!
Clemson, S.C. / Hire ME !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
========================================================================ccplumb@spurge.uwaterloo.ca (Colin Plumb) (11/02/90)
In article <11290@hubcap.clemson.edu> chrisb@hubcap.clemson.edu (Chris Behrens) writes: > The subject says it all... But is there a way to utilize the full > 2 meg, or is this taken up by the DOS formatting ?? Basically, no. The actual capacity is 16,000,000 bits (slightly under the usual definition of a megabyte), and then some is eaten allowing for variation in the rotation speed of the drive and the bit-clock rate, and then you need some sort of sector header, and then comes the big killer.. the gaps around the data blocks to give the read head time to switch to writing and back. It looks like: <header><gap><data><gap><header> During a read, you wait for the header sync mark, read the header to see if it's the desired sector, and if it is, you wait for the data sync mark, then read the data and check the trailing checksum, and usually return with the data. During a write, you do the same thing, except after the header, you check its checksum for validity, then you switch to writing, write a few 0's, a sync mark, the data (and checksum, etc), a few more 0's, and stop writing. The leading 0's are required to make sure your sync mark is sufficiently delayed that it will be overwritten by the next writer, even if you were as fast as the spec allowed to start writing and it is as slow as spec allows. The trailing 0's are just so the last few bits of the block are properly written. You also need more gap after the data block so that even if you're slow to start writing the data, the data clock is a bit slow, and the disk is spinning a bit fast, you don't overwrite the next header. It is possible to fit 10 512-byte sectors on a "1.0 MB" floppy, for 800K effective, due to tighter tolerances these days, and I assume this would let you get 1600K on a "2.0 MB" floppy. The Amiga fits 880K (907.5K if you use some extra space) on a "1.0MB" floppy by writing the entire track at once, requiring only one gap at the end of the track. Then I figured out a really sneaky way to get 1.2 MB ("1.2 MB" 5.25" floppies are 1200K; I got 1.2*1024 K) on a "1.0 MB" floppy. See "Magnetic Recording" Vol.2 by C. Denis Mee and Eric D. Daniels for details. -- -Colin
me@dude.pcs.com (Michael Elbel) (11/12/90)
ccplumb@spurge.uwaterloo.ca (Colin Plumb) writes: > In article <11290@hubcap.clemson.edu> chrisb@hubcap.clemson.edu (Chris Behrens) writes: > > The subject says it all... But is there a way to utilize the full > > 2 meg, or is this taken up by the DOS formatting ?? > It is possible to fit 10 512-byte sectors on a "1.0 MB" floppy, for 800K > effective, due to tighter tolerances these days, and I assume this would > let you get 1600K on a "2.0 MB" floppy. It is possible to fit 11 512-byte sectors on a track reliably if the drive spins not over 302 rpm (300 is the norm). By using 85 tracks (you have to try how far your drive can step) I can format disks to hold 935K on my Atari ST. Michael -- Michael Elbel | Wollen haetten wir schon moegen me@dude.PCS.COM | aber duerfen haben wir uns nicht getraut. | - Karl Valentin
bakke@plains.NoDak.edu (Jeffrey P. Bakke) (11/14/90)
In article <1990Nov1.194908.12296@watdragon.waterloo.edu> ccplumb@spurge.uwaterloo.ca (Colin Plumb) writes: > In article <11290@hubcap.clemson.edu> chrisb@hubcap.clemson.edu (Chris Behrens) writes: > > The subject says it all... But is there a way to utilize the full > > 2 meg, or is this taken up by the DOS formatting ?? > > Basically, no. The actual capacity is 16,000,000 bits (slightly under > ... Explaination about extra information and gaps, etc... In addition to all the needed sector markings, gabs and other informatio that must be included on a disk in order to utilize it, it must also be realized that the original media is never "perfect" in that any errors on the media or faults on the disk surface are taken care of by formatting which simply allows some extra room to account for possible errors. -- Jeffrey P. Bakke | There are a finite number of INTERNET: bakke@plains.NoDak.edu | jokes in the world... UUCP : ...!uunet!plains!bakke | The overflow began BITNET : bakke@plains.bitnet | decades ago. "I am not a number, I am a free man!" - The Prisoner