3.5 floppy

Mark Lloyd wrote:
On 11/15/2017 08:59 PM, Paul wrote:
Ant wrote:


IIRC, 3.5" disks could do 2.88 MB but I think it used compression to
do that?

Apparently, they were just a doubling of density.

http://www.pcguide.com/ref/fdd/formatKB2880-c.html

And they were a flop commercially.

Paul

Also, disk compression claimed a doubling of capacity, but except in
very unusual circumstances was more like 1.2 times than 2.

Hey, we don't want to give away any secrets now.

Andy thinks a compressor doubles, so we'll just leave it at that.

*******

If you try:

dd.exe if=/dev/random of=samplefile.bin bs=1024 count=1000

and try and compress that, it shouldn't compress at all.

So it won't even be 1.2 times.

Incompressible data is ... not compressible.
What the compressor does in such cases, is inserts its header
in front of the file, and the header will declare "payload not
compressed" as leaving it uncompressed is the best you can do.
The compressor works at it, but notices the compression ratio
is no damn good, so it punts and just slaps a header on the
file, declaring defeat. It's like when your car hits
a brick wall, and the "check engine" light comes on :-)
I tried to use 7Z Ultra on this, and the output is *bigger*
than the original file.

Directory of H:\

11/16/2017 04:45 PM 1,024,000 samplefile.bin
11/16/2017 04:46 PM 1,024,196 samplefile.bin.7z

You can see the impact of making that test file larger, and how much
the header scheme adds. This tells you the compressor likely
works in "chunks" of some particular size.

Directory of H:\

11/16/2017 05:17 PM 1,024,000,000 samplefile.bin
11/16/2017 05:26 PM 1,024,054,451 samplefile.bin.7z

Whereas if you make a second file like this

dd.exe if=/dev/zero of=zerofile.bin bs=1024 count=1000

that file will compress like gang-busters. The ratio is 2917x.
I could store a zillion of these "easy" files on my
compressing floppy.

Directory of H:\

11/16/2017 04:47 PM 1,024,000 zerofile.bin
11/16/2017 04:48 PM 351 zerofile.bin.7z

Real life is somewhere between those two extremes.

*******

In the year 2017, many pieces of media may have
attempted compression on their own. Some PDFs for
example, might not compress all that well. Microsoft
Word has a default encryptor (encrypts with the default
password, so it isn't actually password protected), and
any time you encrypt a file, the random data patterns
involved don't compress. This is one reason, if you
use GPG (GNU Privacy Guard) and prepare a file, it
compresses the file first, before it encrypts it.
If the order was reversed, the file would be huge.

Really, the results can be quite variable. Compression
results factor in the nature of what you're compressing,
as well as the "class" of compressor you are using. A
compressor that "runs fast", generally doesn't compress
all that well.

Paul

Andy wrote:
That is correct Ant

Yay, I can remember correctly again. :P
--
Quote of the Week: "I go out of my way to avoid stepping on ants." --Terry McGovern, daughter of Senator George and Eleanor McGovern, subject of the book "Terry by her father"
Note: A fixed width font (Courier, Monospace, etc.) is required to see this signature correctly.
/\___/\ Ant(Dude) @ http://antfarm.ma.cx (Personal Web Site)
/ /\ /\ \ Ant's Quality Foraged Links: http://aqfl.net
| |o o| |
\ _ / Please nuke ANT if replying by e-mail privately. If credit-
( ) ing, then please kindly use Ant nickname and AQFL URL/link.