Soft vs Hard Sectored

[Lorne]

Can someone please provide me an explanation of the difference between soft and hard sectored floppy disks?
I did a search for "soft sectored" on the forums and came up with 22 threads, which took about 15 mins to go through, and none of them appear to explain the difference.

Also, does it have something to do with one hole vs multiple holes in the disks? (I have some 8" 1S/1D disks that are Wang Compatible and hard sectored. They have a bunch of holes around the mounting ring).

 

[patscc]

Soft vs. Hard sectored

Soft vs. Hard sectored

Ok, I'll take a stab at a simple explanation.
The holes are reference points the controller uses to find the beginning of a sector.

The beginning of a sector is important because there is usually a "window", or lead-in area that circuitry uses to synch to the signals coming from the head. When it's all in sync, data is read (more or less, this is simplified)

The hard-sectored formats use a hole per sector. It was a simple way to let the controller know that a new sector had started. Hard-sector formats are tyrpically locked to the drive they were designed for.

At some point someone figured out that you can get away with one hole, as long as you use a slightly more sophisticated controller that keeps track of timing signals, and essentially begins counting when it sees the one hole. This works since each sector, as far as the controller is concerned, and as far as FM & MFM, two popular recording formats (there's also GCR, but I'm leaving that out), are concerend, are well-layed out, and there for easy to count.

This is simplified, so if there are questions, or if there's anything glaringly wrong, please post.

patscc

 

[MikeS]

A pretty good explanation; nothing wrong, just a few additional points:

The hard sector disks usually have an extra hole 1/2 way between two sector holes; that's the index hole, to tell the controller where the first sector starts.

Hard-sector disks aren't really locked to any particular drive, just the disk controller (like any other format). Some newer drives won't go ready when they see multiple "index" pulses, but most drives will not know or care how many holes there are and just pass it on to the controller to sort out.

And even one index hole isn't really *required* for some soft sector controllers, since they read the data on the disk to find out where each sector is located; in fact most Commodore drives (to name just one make) do not even have a sensor to read the index hole, which is why the disks could be turned upside down to use both sides in a single-sided drive. The main purpose for the index hole in a soft-sector disk is to sense that there is a disk inserted and it's rotating (at the right speed).

 

[Chuck(G)]

Basicallly, you got it right. Hard-sectored floppies have a hole for each "sector", in addition to the regular index hole, which is placed mid-way between two sector holes.

Both types require some sort of lead-in sync pattern and almost all have some sort address encoded, so the electronics required for both are about the same.

The difference is in efficiency. With a soft-sectored disk, the speed of the media has to be more or less constant over an entire disk revolution. This leads to lots of "gap" padding (a write made when the drive is turning somewhat faster will occupy more physical space on the disk). In fact, if one looks at a plain old 9 sector MS-DOS "360K" diskette, more than a quarter of the diskette is taken up by "overhead". On a 26 sector 128-byte SSSD 8", the number is more like 35 percent.

But a hard-sectored disk drive needs only regulate its speed over a sector (when you hit the next hole, you're done), so the need for gaps and padding is much lower.

So, while an 8" soft-sectored disk using 128 byte FM sectors can safely fit only about 26 sectors, a hard-sectored disk is good for 32. There is only one common sectoring scheme for 8" disks--32 sector, but many 8" drives have dividers that can provide 16 and 8 sector pulses also.

On the other hand, 5.25" HS disks are available in 8, 10 and 16 sectors.

As electronics and motor control improved, soft-sectored diskettes could match the performance of hard-sectored media and the old HS media became obsolete. (Remember that DOS 1.x used 8-sector 320K floppies and didn't go to 9 sector 360K until DOS 2.0).

But many word-processing setups hung onto hard-sectored media for a very long time. (Wang and Lanier for example).

There were also hard-sectored hard disks, with sector notches cut into a platter to mark sectors.

 

[Lorne]

So from what I read so far, I can use a hard sectored disk in place of a soft sectored disk? (or am I missing something?)

 

[patscc]

hard/soft

hard/soft

No(ish). If the soft-sector controller expects to see 1 index hole per revolution, it will get confused by multiple holes. That's not to say there aren't some controllers out that can do it, but I don't know any.
Remember, while the software controllers keep track of what sector they're on by counting( it's more complex, but counting is the basic idea), when they see that index hole, the count gets reset.
Like MikeS said, if the controller doesn't need a index hole to begin with, then it wouldn't care about the extra holes.
Experiment. Take a DSDD PC disk, drill a second index hole into it, and see what happens.

patscc

 

[Chuck(G)]

Some 8" drives can separate the "index" from "sector" holes (some of the many jumpers that you find on the drives) and output a separate "sector" signal, while outputting only one index pulse per revolution. You *can* use hard-sectored media as soft-sectored in those.

Of course it'll confuse the dickens out of the people to whom you send your disks.

 

[Dwight Elvey]

So from what I read so far, I can use a hard sectored disk in place of a soft sectored disk? (or am I missing something?)

Hi
In many cases, you can format a hard sectored disk as a soft sectored
disk, as long as the drive doesn't expect the single hole to indicate
that the drive is ready( this is no true for many of the newer drives ).
The controller determines if you need hard or soft sectored. You can not
use a soft sectored disk with a hard sectored controller but as mentioned
before you can often use a hard sectored disk with a soft sectored controller.
On a hard sectored disk, there are many ways of keeping track of which
sector is currently under the head. As others mentioned, they may just
count sector holes from the index hole but in most cases, each sector has
a header before the data that includes the sector number and the track number.
In hard sectored, the controller knows to expect to see synch bytes, header
and the data following each of the sector holes.
In soft sectored, the controller watches for data/clock sequences that
would otherwise be illegal as data information. Usually there are several
types of these marks so that the controller can distiguish headers from
sector data or others, like deleted sector ( often used to mark a bad
sector ).
One of the others mentioned that soft sectored controllers keep track
of the sector by counting. This is not true, they actual just look at
each sector they come to and see if it matched the requested one
by reading the header. This is also true of most hard sectored although,
my Nicolet 1080 only puts only the track number as a header for the first sector
and counts holes for the next sector ( it uses 32 hole hard sectored disk
but partitions it into two large sectors, each 16 holes long ).
By determining the sector by reading the header, it is possible
to format the disk in such a way that the sectors are not in sequential
order. This is often done on slower machines that can not read
a second sector right after reading the first sector. It may have
to skip a sector before it is ready to read the next sector. If the
disk is formatted in sequential sector order, it would have to
wait an entire revolution before it could read the next sequential
sector. By skipping every other sector it could read the next
sector just as it was coming under the head. This is often called
interleaving. I do this on my H89 for the Heathkit basic. It can
make things load much faster.
Dwight

 

[Chuck(G)]

Depends on the drive, Dwight.

Most soft-sectored controllers use the index hole to terminate as well as initiate a format. Many also use the index hole to determine when a sector IAM can't be found. So if you have a drive that just passes sector holes as index holes, you're out of luck using HS as SS.

5.25" drives tend to be extremely stupid in this matter.

I wrote some code for a little 8-pin PIC that hangs off a drive and looks to see if HS or SS media is inserted. If SS, it synthesizes the HS pulses. If HS, it just passes them through.

 

[patscc]

drives

drives

I figured there were some combinations out there that I'd know nothing about.

Does anyone have any known drive/controller combinations that support this ?

patscc

 

[NobodyIsHere]

[snip]

I wrote some code for a little 8-pin PIC that hangs off a drive and looks to see if HS or SS media is inserted. If SS, it synthesizes the HS pulses. If HS, it just passes them through.

Hi Chuck, some people were asking about that 8 pin PIC project to synthesize HS holes on the NorthStar_Computers mailing list. Maybe its time to ask for some testing volunteers there? I'll bet there are some interested parties who would really like to see that project come about.

Thanks and have a nice day!

Andrew Lynch

 

[hmb]

Hi Chuck, some people were asking about that 8 pin PIC project to synthesize HS holes on the NorthStar_Computers mailing list. Maybe its time to ask for some testing volunteers there? I'll bet there are some interested parties who would really like to see that project come about.

Thanks and have a nice day!

Andrew Lynch

You mean like this "virtual sector generator" for 5.25" floppy drives ?

VSG

Virtual Sector Generator

deramp.com

 

[Chuck(G)]

Yes, I thought that had been handled by others. My work involves reading the blasted things, not writing them, so the project would be of little use to me.