Did 5.25" floppies undergo a change in magnetic coating?
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3.5" floppy disks, in the transition from 720K to 1.44M, changed the actual coating to a different compound that was magnetically 'stiffer'. This was necessary to support the higher density, but meant the old disks could not support the new high-density format even if used in a new drive. A more subtle and much nastier problem: if you formatted a new disk in an old drive, everything would seem fine, but the information would not have been recorded strongly enough, and might fade over the next few days.
5.25" floppies made several format transitions that together accomplished an order of magnitude capacity increase until the final 1.2M format. Did any of these transitions involve a similar change in the actual coating? Or did the disks themselves stay interchangeable apart from issues of hard versus soft sectors?
history hardware floppy-disk
asked Mar 4 at 19:17
rwallacerwallace
10.2k451150
add a comment |
3.5" floppy disks, in the transition from 720K to 1.44M, changed the actual coating to a different compound that was magnetically 'stiffer'. This was necessary to support the higher density, but meant the old disks could not support the new high-density format even if used in a new drive. A more subtle and much nastier problem: if you formatted a new disk in an old drive, everything would seem fine, but the information would not have been recorded strongly enough, and might fade over the next few days.
5.25" floppies made several format transitions that together accomplished an order of magnitude capacity increase until the final 1.2M format. Did any of these transitions involve a similar change in the actual coating? Or did the disks themselves stay interchangeable apart from issues of hard versus soft sectors?
history hardware floppy-disk
asked Mar 4 at 19:17
rwallacerwallace
10.2k451150
I had 3.5 and 5.25" HD Floppy drives in 1989 in a brand new 286, and friends had a variety of 720k and 360k drives. I don't recall ever having read problems other than when accidentally taking a 1.2 or 1.44MB disk to someone who didn't have a HD drive. So it was possibly dependent on the quality of the non-HD drives used to do the reading.
– Criggie
Mar 5 at 11:16
1
In a pinch you could punch a hole in the top of a 3.5" DD disk to turn it into a HD disk. It would generally work to transfer large files, but you knew never to really rely on it lasting.
– JPhi1618
Mar 5 at 16:37
add a comment |
3.5" floppy disks, in the transition from 720K to 1.44M, changed the actual coating to a different compound that was magnetically 'stiffer'. This was necessary to support the higher density, but meant the old disks could not support the new high-density format even if used in a new drive. A more subtle and much nastier problem: if you formatted a new disk in an old drive, everything would seem fine, but the information would not have been recorded strongly enough, and might fade over the next few days.
5.25" floppies made several format transitions that together accomplished an order of magnitude capacity increase until the final 1.2M format. Did any of these transitions involve a similar change in the actual coating? Or did the disks themselves stay interchangeable apart from issues of hard versus soft sectors?
history hardware floppy-disk
asked Mar 4 at 19:17
rwallacerwallace
10.2k451150
3.5" floppy disks, in the transition from 720K to 1.44M, changed the actual coating to a different compound that was magnetically 'stiffer'. This was necessary to support the higher density, but meant the old disks could not support the new high-density format even if used in a new drive. A more subtle and much nastier problem: if you formatted a new disk in an old drive, everything would seem fine, but the information would not have been recorded strongly enough, and might fade over the next few days.
5.25" floppies made several format transitions that together accomplished an order of magnitude capacity increase until the final 1.2M format. Did any of these transitions involve a similar change in the actual coating? Or did the disks themselves stay interchangeable apart from issues of hard versus soft sectors?
history hardware floppy-disk
history hardware floppy-disk
asked Mar 4 at 19:17
rwallacerwallace
10.2k451150
asked Mar 4 at 19:17
rwallacerwallace
10.2k451150
asked Mar 4 at 19:17
rwallacerwallace
10.2k451150
asked Mar 4 at 19:17
rwallacerwallace
10.2k451150
asked Mar 4 at 19:17
rwallacerwallace
10.2k451150
10.2k451150
I had 3.5 and 5.25" HD Floppy drives in 1989 in a brand new 286, and friends had a variety of 720k and 360k drives. I don't recall ever having read problems other than when accidentally taking a 1.2 or 1.44MB disk to someone who didn't have a HD drive. So it was possibly dependent on the quality of the non-HD drives used to do the reading.
– Criggie
Mar 5 at 11:16
1
In a pinch you could punch a hole in the top of a 3.5" DD disk to turn it into a HD disk. It would generally work to transfer large files, but you knew never to really rely on it lasting.
– JPhi1618
Mar 5 at 16:37
add a comment |
I had 3.5 and 5.25" HD Floppy drives in 1989 in a brand new 286, and friends had a variety of 720k and 360k drives. I don't recall ever having read problems other than when accidentally taking a 1.2 or 1.44MB disk to someone who didn't have a HD drive. So it was possibly dependent on the quality of the non-HD drives used to do the reading.
– Criggie
Mar 5 at 11:16
1
In a pinch you could punch a hole in the top of a 3.5" DD disk to turn it into a HD disk. It would generally work to transfer large files, but you knew never to really rely on it lasting.
– JPhi1618
Mar 5 at 16:37
I had 3.5 and 5.25" HD Floppy drives in 1989 in a brand new 286, and friends had a variety of 720k and 360k drives. I don't recall ever having read problems other than when accidentally taking a 1.2 or 1.44MB disk to someone who didn't have a HD drive. So it was possibly dependent on the quality of the non-HD drives used to do the reading.
– Criggie
Mar 5 at 11:16
I had 3.5 and 5.25" HD Floppy drives in 1989 in a brand new 286, and friends had a variety of 720k and 360k drives. I don't recall ever having read problems other than when accidentally taking a 1.2 or 1.44MB disk to someone who didn't have a HD drive. So it was possibly dependent on the quality of the non-HD drives used to do the reading.
– Criggie
Mar 5 at 11:16
1
1
In a pinch you could punch a hole in the top of a 3.5" DD disk to turn it into a HD disk. It would generally work to transfer large files, but you knew never to really rely on it lasting.
– JPhi1618
Mar 5 at 16:37
In a pinch you could punch a hole in the top of a 3.5" DD disk to turn it into a HD disk. It would generally work to transfer large files, but you knew never to really rely on it lasting.
– JPhi1618
Mar 5 at 16:37
add a comment |
1 Answer
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The main technical parameter for a floppy disk's coating is its coercivity, i.e. the resistance of ferromagnetic matter to withstand demagnetization. Coercivity is measured in Oersted, after Hans Christian Ørsted, a Danish physicist who discovered the magnetic impact of electrical current.
- 5¼" disks storing 360K and 720K (SD and DD) used a coating with a coercivity of 300 Oersted.
- 5¼" disks storing 1.2M used a coating with a coercivity of 600 Oersted.
So yes, the coating was changed to support the HD format.
The difference between 5¼" DD and HD coating is much larger than the same difference between 3½" DD and HD media - which are 660 Oe and 720 Oe, respectively.
edited Mar 5 at 16:48
Toby Speight
274312
answered Mar 4 at 20:56
tofrotofro
16.3k33392
2
Do you have any idea why the difference in 3.5" was smaller? Is it because DD had already a higher than needed coercivity (by the way, you have a typo there) from the beginning? Does that also mean that they could have produced DD-compatible drives with higher capacity instead of introducing a slightly different coating?
– Selcuk
Mar 5 at 2:30
2
@Selcuk: The challenge has always been bit density, i.e. how many bits can you store per mm2. Since 3 1/2" disks are a lot smaller (area varies with the square of the diameter), even their initial 720KB capacity required a bit density on par with the 1.2MB size 5 1/4" disks. As for the 1.44MB format, that's mostly due to MFM encoding.
– MSalters
Mar 5 at 13:58
1
@MSalters The much smaller size of 3.5" disks compared to 5 1/4" would have been my explanation as well. Also, if you look at the percentage of the overall disk surface area actually reachable (thus, used) by the heads on a 3.5" disk vs. a 5 1/4" disk, that is way lower for the 3.5" floppy.
– tofro
Mar 5 at 16:26
According to Wikipedia 5.25" "DD" disk capacity was 360K (a 800K variant existed); while "QD" was 720K. My second computer used 360K disks so I was very confused when I read your answer saying 360K was "SD" and not "DD".
– Martin Rosenau
Mar 6 at 6:23
add a comment |
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The main technical parameter for a floppy disk's coating is its coercivity, i.e. the resistance of ferromagnetic matter to withstand demagnetization. Coercivity is measured in Oersted, after Hans Christian Ørsted, a Danish physicist who discovered the magnetic impact of electrical current.
- 5¼" disks storing 360K and 720K (SD and DD) used a coating with a coercivity of 300 Oersted.
- 5¼" disks storing 1.2M used a coating with a coercivity of 600 Oersted.
So yes, the coating was changed to support the HD format.
The difference between 5¼" DD and HD coating is much larger than the same difference between 3½" DD and HD media - which are 660 Oe and 720 Oe, respectively.
edited Mar 5 at 16:48
Toby Speight
274312
answered Mar 4 at 20:56
tofrotofro
16.3k33392
2
Do you have any idea why the difference in 3.5" was smaller? Is it because DD had already a higher than needed coercivity (by the way, you have a typo there) from the beginning? Does that also mean that they could have produced DD-compatible drives with higher capacity instead of introducing a slightly different coating?
– Selcuk
Mar 5 at 2:30
2
@Selcuk: The challenge has always been bit density, i.e. how many bits can you store per mm2. Since 3 1/2" disks are a lot smaller (area varies with the square of the diameter), even their initial 720KB capacity required a bit density on par with the 1.2MB size 5 1/4" disks. As for the 1.44MB format, that's mostly due to MFM encoding.
– MSalters
Mar 5 at 13:58
1
@MSalters The much smaller size of 3.5" disks compared to 5 1/4" would have been my explanation as well. Also, if you look at the percentage of the overall disk surface area actually reachable (thus, used) by the heads on a 3.5" disk vs. a 5 1/4" disk, that is way lower for the 3.5" floppy.
– tofro
Mar 5 at 16:26
According to Wikipedia 5.25" "DD" disk capacity was 360K (a 800K variant existed); while "QD" was 720K. My second computer used 360K disks so I was very confused when I read your answer saying 360K was "SD" and not "DD".
– Martin Rosenau
Mar 6 at 6:23
add a comment |
The main technical parameter for a floppy disk's coating is its coercivity, i.e. the resistance of ferromagnetic matter to withstand demagnetization. Coercivity is measured in Oersted, after Hans Christian Ørsted, a Danish physicist who discovered the magnetic impact of electrical current.
- 5¼" disks storing 360K and 720K (SD and DD) used a coating with a coercivity of 300 Oersted.
- 5¼" disks storing 1.2M used a coating with a coercivity of 600 Oersted.
So yes, the coating was changed to support the HD format.
The difference between 5¼" DD and HD coating is much larger than the same difference between 3½" DD and HD media - which are 660 Oe and 720 Oe, respectively.
edited Mar 5 at 16:48
Toby Speight
274312
answered Mar 4 at 20:56
tofrotofro
16.3k33392
2
Do you have any idea why the difference in 3.5" was smaller? Is it because DD had already a higher than needed coercivity (by the way, you have a typo there) from the beginning? Does that also mean that they could have produced DD-compatible drives with higher capacity instead of introducing a slightly different coating?
– Selcuk
Mar 5 at 2:30
2
@Selcuk: The challenge has always been bit density, i.e. how many bits can you store per mm2. Since 3 1/2" disks are a lot smaller (area varies with the square of the diameter), even their initial 720KB capacity required a bit density on par with the 1.2MB size 5 1/4" disks. As for the 1.44MB format, that's mostly due to MFM encoding.
– MSalters
Mar 5 at 13:58
1
@MSalters The much smaller size of 3.5" disks compared to 5 1/4" would have been my explanation as well. Also, if you look at the percentage of the overall disk surface area actually reachable (thus, used) by the heads on a 3.5" disk vs. a 5 1/4" disk, that is way lower for the 3.5" floppy.
– tofro
Mar 5 at 16:26
According to Wikipedia 5.25" "DD" disk capacity was 360K (a 800K variant existed); while "QD" was 720K. My second computer used 360K disks so I was very confused when I read your answer saying 360K was "SD" and not "DD".
– Martin Rosenau
Mar 6 at 6:23
add a comment |
The main technical parameter for a floppy disk's coating is its coercivity, i.e. the resistance of ferromagnetic matter to withstand demagnetization. Coercivity is measured in Oersted, after Hans Christian Ørsted, a Danish physicist who discovered the magnetic impact of electrical current.
- 5¼" disks storing 360K and 720K (SD and DD) used a coating with a coercivity of 300 Oersted.
- 5¼" disks storing 1.2M used a coating with a coercivity of 600 Oersted.
So yes, the coating was changed to support the HD format.
The difference between 5¼" DD and HD coating is much larger than the same difference between 3½" DD and HD media - which are 660 Oe and 720 Oe, respectively.
edited Mar 5 at 16:48
Toby Speight
274312
answered Mar 4 at 20:56
tofrotofro
16.3k33392
The main technical parameter for a floppy disk's coating is its coercivity, i.e. the resistance of ferromagnetic matter to withstand demagnetization. Coercivity is measured in Oersted, after Hans Christian Ørsted, a Danish physicist who discovered the magnetic impact of electrical current.
- 5¼" disks storing 360K and 720K (SD and DD) used a coating with a coercivity of 300 Oersted.
- 5¼" disks storing 1.2M used a coating with a coercivity of 600 Oersted.
So yes, the coating was changed to support the HD format.
The difference between 5¼" DD and HD coating is much larger than the same difference between 3½" DD and HD media - which are 660 Oe and 720 Oe, respectively.
edited Mar 5 at 16:48
Toby Speight
274312
answered Mar 4 at 20:56
tofrotofro
16.3k33392
edited Mar 5 at 16:48
Toby Speight
274312
edited Mar 5 at 16:48
Toby Speight
274312
edited Mar 5 at 16:48
Toby Speight
274312
274312
answered Mar 4 at 20:56
tofrotofro
16.3k33392
answered Mar 4 at 20:56
tofrotofro
16.3k33392
answered Mar 4 at 20:56
tofrotofro
16.3k33392
16.3k33392
2
Do you have any idea why the difference in 3.5" was smaller? Is it because DD had already a higher than needed coercivity (by the way, you have a typo there) from the beginning? Does that also mean that they could have produced DD-compatible drives with higher capacity instead of introducing a slightly different coating?
– Selcuk
Mar 5 at 2:30
2
@Selcuk: The challenge has always been bit density, i.e. how many bits can you store per mm2. Since 3 1/2" disks are a lot smaller (area varies with the square of the diameter), even their initial 720KB capacity required a bit density on par with the 1.2MB size 5 1/4" disks. As for the 1.44MB format, that's mostly due to MFM encoding.
– MSalters
Mar 5 at 13:58
1
@MSalters The much smaller size of 3.5" disks compared to 5 1/4" would have been my explanation as well. Also, if you look at the percentage of the overall disk surface area actually reachable (thus, used) by the heads on a 3.5" disk vs. a 5 1/4" disk, that is way lower for the 3.5" floppy.
– tofro
Mar 5 at 16:26
According to Wikipedia 5.25" "DD" disk capacity was 360K (a 800K variant existed); while "QD" was 720K. My second computer used 360K disks so I was very confused when I read your answer saying 360K was "SD" and not "DD".
– Martin Rosenau
Mar 6 at 6:23
add a comment |
2
Do you have any idea why the difference in 3.5" was smaller? Is it because DD had already a higher than needed coercivity (by the way, you have a typo there) from the beginning? Does that also mean that they could have produced DD-compatible drives with higher capacity instead of introducing a slightly different coating?
– Selcuk
Mar 5 at 2:30
2
@Selcuk: The challenge has always been bit density, i.e. how many bits can you store per mm2. Since 3 1/2" disks are a lot smaller (area varies with the square of the diameter), even their initial 720KB capacity required a bit density on par with the 1.2MB size 5 1/4" disks. As for the 1.44MB format, that's mostly due to MFM encoding.
– MSalters
Mar 5 at 13:58
1
@MSalters The much smaller size of 3.5" disks compared to 5 1/4" would have been my explanation as well. Also, if you look at the percentage of the overall disk surface area actually reachable (thus, used) by the heads on a 3.5" disk vs. a 5 1/4" disk, that is way lower for the 3.5" floppy.
– tofro
Mar 5 at 16:26
According to Wikipedia 5.25" "DD" disk capacity was 360K (a 800K variant existed); while "QD" was 720K. My second computer used 360K disks so I was very confused when I read your answer saying 360K was "SD" and not "DD".
– Martin Rosenau
Mar 6 at 6:23
2
2
Do you have any idea why the difference in 3.5" was smaller? Is it because DD had already a higher than needed coercivity (by the way, you have a typo there) from the beginning? Does that also mean that they could have produced DD-compatible drives with higher capacity instead of introducing a slightly different coating?
– Selcuk
Mar 5 at 2:30
Do you have any idea why the difference in 3.5" was smaller? Is it because DD had already a higher than needed coercivity (by the way, you have a typo there) from the beginning? Does that also mean that they could have produced DD-compatible drives with higher capacity instead of introducing a slightly different coating?
– Selcuk
Mar 5 at 2:30
2
2
@Selcuk: The challenge has always been bit density, i.e. how many bits can you store per mm2. Since 3 1/2" disks are a lot smaller (area varies with the square of the diameter), even their initial 720KB capacity required a bit density on par with the 1.2MB size 5 1/4" disks. As for the 1.44MB format, that's mostly due to MFM encoding.
– MSalters
Mar 5 at 13:58
@Selcuk: The challenge has always been bit density, i.e. how many bits can you store per mm2. Since 3 1/2" disks are a lot smaller (area varies with the square of the diameter), even their initial 720KB capacity required a bit density on par with the 1.2MB size 5 1/4" disks. As for the 1.44MB format, that's mostly due to MFM encoding.
– MSalters
Mar 5 at 13:58
1
1
@MSalters The much smaller size of 3.5" disks compared to 5 1/4" would have been my explanation as well. Also, if you look at the percentage of the overall disk surface area actually reachable (thus, used) by the heads on a 3.5" disk vs. a 5 1/4" disk, that is way lower for the 3.5" floppy.
– tofro
Mar 5 at 16:26
@MSalters The much smaller size of 3.5" disks compared to 5 1/4" would have been my explanation as well. Also, if you look at the percentage of the overall disk surface area actually reachable (thus, used) by the heads on a 3.5" disk vs. a 5 1/4" disk, that is way lower for the 3.5" floppy.
– tofro
Mar 5 at 16:26
According to Wikipedia 5.25" "DD" disk capacity was 360K (a 800K variant existed); while "QD" was 720K. My second computer used 360K disks so I was very confused when I read your answer saying 360K was "SD" and not "DD".
– Martin Rosenau
Mar 6 at 6:23
According to Wikipedia 5.25" "DD" disk capacity was 360K (a 800K variant existed); while "QD" was 720K. My second computer used 360K disks so I was very confused when I read your answer saying 360K was "SD" and not "DD".
– Martin Rosenau
Mar 6 at 6:23
add a comment |
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I had 3.5 and 5.25" HD Floppy drives in 1989 in a brand new 286, and friends had a variety of 720k and 360k drives. I don't recall ever having read problems other than when accidentally taking a 1.2 or 1.44MB disk to someone who didn't have a HD drive. So it was possibly dependent on the quality of the non-HD drives used to do the reading.
– Criggie
Mar 5 at 11:16
1
In a pinch you could punch a hole in the top of a 3.5" DD disk to turn it into a HD disk. It would generally work to transfer large files, but you knew never to really rely on it lasting.
– JPhi1618
Mar 5 at 16:37