Dec 102017
Turn 720K disks to 1.44 mb.
File 144DI$K.ZIP from The Programmer’s Corner in
Category Tutorials + Patches
Turn 720K disks to 1.44 mb.
File Name File Size Zip Size Zip Type
144DISK.TXT 10461 3824 deflated

Download File 144DI$K.ZIP Here

Contents of the 144DISK.TXT file

Converting 720 KB microdisks to 1.44 MB format
with an additional article from IBM
Compiled and written by
A. D. Longton of Rockville, M.D.

High density 3.5" disks are now selling for $40-70 a box in some
stores, much more then twice the price of regular 720 KB disks.
Fortunately, I can give you a price break and you don't have to
give me a cent. For the same price of 720 KB disks, you can have
1.44 MB disks.

"What do I need?"

A 1.44 MB 3-1/2 inch microdisk drive.
One 3-1/2 inch, 720 KB disk.
Sodering iron.

"How long will it take me to get them??"

10 minutes for a box of ten disks, less per disk if you make

"Is it safe???"

Yes, as long as you are not drunk and burn yourself with the
sodering iron. I have formated 25 disks and only ONE would not
accept a full system and allow for a total of 1.44 MB. That disk
would not format to a full 720 KB either! To date I have not lost
any data that I have stored on the modified disks. I am using one
of them to store this file right now. This procedure is more
reliable then special formating programs that add only 80k to your
720 KB disks. You do not have to use any special drivers to use
your new disks either. ( * SEE below for comments from IBM
concerning 3.5" disks. * )

What do I do?

1. Go find a sodering iron that has a round shaft that can
just about fit through the write-protect hole on a 3.5" disk.

2. Plug it in and read on.

3. What you are going to do is melt a hole through the upper
left corner of the disk.(see diagram) This hole is one of
the only things that makes 720 KB disks different from 1.44
MB disks.

4. To locate this new hole, take two blank 3.5 inch disks
side by side and face them in the same direction as the
diagram below. Now, close them like a sandwich.

5. Hold the two disks together so that they do not overlap
each other.
| __ | | __ |
1.44 MB format ==> |(__) | F R O N T | [__]| <== Write-protect
enable hole | | S I D E | | hole
| | | |
| | | |
| | | |
| | | |
| \________________/ |
| ______________ |
| | _ MICRO DISK| |
| | | | | |
| | |_| 135 TPI | |

6. Take a pen and mark the CENTER of the space created by one of
the write protect tab holes. The one that you mark will be your
test disk.

7. Take the hot sodering iron and punch a hole through the spot on
the test disk.

8. Shave off any excess plastic with the knife. Do not get ANY
particles in the case.

9. Format the disk. (Requires DOS 3.3 or a 1.44 MB disk software

That's it! After doing this once you should have no problem
repeating the procedure.

CAUTION: DO NOT use a drill to make the hole. If you do plastic
may get in the case and destroy everything you put there. If you
have any question about the safety of this operation you can use
disk diagnostics to check out the integrity of the test disk you
make. I leave the testing to you and take no responsibility for
the failure or sucess of this process, though I have had no
problems. One suggestion: try using a couple of these disks to
store backups of downloads from BBS'. Check the zipped and arced
files after the disks have been used, erased, and reused a couple
times. At worst you will have to fill the hole and reformat the
disk to 720 KB. The disks that I tested this on were
bottom-of-the-line SKC brand ($14 a box at Crown Books) and two or
three Precision and Platinum brand disks. This result has also
been promised by a company that advertises in computer magazines
such as PC Magazine. They charge about $30 for thier product
(probably a sodering iron) and a box of 10 generic disks.

On a very technical side, but one that is not yet ready to aspire
to such crudeness, here is what IBM says....

Kevin Maier
IBM Corporation
Boca Raton, Florida
"Reprinted by permission of the
IBM Personal Systems Technical Journal."
Page 42, issue 2, 1989

"The original recommendations about the proper formatting and use
of PS/2 diskettes have undergone revision. This article explains
why the recommendations have changed.


Personal System/2 shipping cartons include a sheet of paper that
cautions users not to format a 2.0 MB diskette to 720 KB, because
the diskette becomes unusable and should be discarded.

This caution was issued because of the physical properties of 720
KB diskettes versus 1.44 MB diskettes. The 720 KB format uses a
higher write current, and the 1.44 MB format uses a lower write
current. To accommodate the higher write current, the oxide
coating on a 1.0 MB (720 KB formatted) diskette is denser than the
oxide coating on a 2.0 MB (1.44 MB formatted) diskette.

When you format a 2.0 MB diskette to 720 KB, you apply the higher
write current to the less dense oxide coating. The hardware
developers originally felt that this meant the 720 KB formatting
pattern is written too deeply into the 2.0 MB oxide coating,
causing intermittent data errors and unreliable use. Furthermore,
the developers felt that if you attempted to reformat the diskette
to 1.44 MB, which uses the lower write current, the 1.44 MB format
would not completely write over the "deeper" 720 KB format.
Therefore the developers' recommendation was to discard a 2.0 MB
diskette that was formatted to 720 KB.


Since the time that this caution was issued, the developers have
performed additional testing, and have concluded that there is no
need to discard a 2.0 MB diskette that was formatted to 720 KB.

It is still true that a 2.0 MB diskette formated to 720 KB will
cause intermittent data errors. However, the latest assessment is
that you will be able to reformat the diskette to 1.44 MB and use
it reliably after that.

The same logic applies to a 1.0 MB diskette formatted to 1.44 MB.
You cannot use it with the 1.44 MB format, but you can reformat it
to 720 KB and use it reliably after that.

Therefore, the current recommendation is: If you format a
diskettte to the wrong capacity, do not discard it; instead,
reformat it correctly and use it."

With all those feelings and recomendations on those feelings it
makes me wonder how much experimentation was actually being done
on a strictly scientific level. Note that the one mention of
formatting 1.0mb disks to 1.44 MB does not say that you will get
errors if you use them. What it does say is that if you reformat
that wrongly formatted disk, you can reliably use it at 720 KB.
The implication is that since there were errors with 2.0mb disks
formatted to 720 KB "logic applies" that there will be errors if
the reverse is done. This is not necessarly the case, and we are
not told why, we are just told.

FYI, here are the specifications for the 720 KB, 1.44 MB, and 360k
5.25" disk drives as listed in the same issue on pages 43-44.
Note the large similarity between 360k and 720 KB disks and 720 KB
disks and 1.44 MB disks.

720 KB and 1.44 MB Diskette Drives

720 KB 1.44 MB 360 KB (5.25")
Access time:
Track-to-track 6 ms 6 ms 6 ms
Head settle time 15 ms 15 ms 15 ms
Motor start time 500 ms 500 ms 750 ms^

Disk rotational speed: 300 rpm 300 rpm 300 rpm
Maximum Latency 200 ms 200 ms 200 ms
Formatted Characteristics: 720 KB 1.44 MB^ 360 KB^
Tracks (actual) 80 80 40 ^
Tracks per inch 135 tpi 135 tpi 48 ^
Sectors per track 9 18 ^ 9
Bytes per sector 512 512 512
Bytes per track 4608 9216 ^ 4608
Data heads 2 2 2
Sector interleave factor 1:1 1:1 1:1
Sector skew factor 0 0 0
Sectors per cluster 2 1 ^ 2

Transfer rate 250,000 500,000^ 250,000
(bits per second)

(All ^'ed numbers are numbers that are different from the 720 KB

"...if they think you're technical, go crude. ....
These days, though, you have to be pretty technical before
you can even aspire to crudeness."

--From William Gibson's short story
Johnny Mnemonic

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