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Re: DD bs=4M option on USB mem-stick creates false format




Hi,

kAt wrote:
> I am trying to find out
> what firmware works with this medium and what it really does.

It's a little computer which implements USB bus operation, and a subset
of the SCSI command protocol, and also manages the mapping from logical
addresses (LBA) to physical addresses.
What it does internally becomes mostly of interest if it cheats on you.
(Multiple block mapping and keyboard simulation are known.)


> I suspect the chips are the same memory chips one finds in a ddr/dram

Not at all. The memory technology is about whether they keep their
memory without electrical power supply
  https://en.wikipedia.org/wiki/Flash_memory
  https://en.wikipedia.org/wiki/Dynamic_random-access_memory


> using a USBstick as additional Ram.

... and a formatted 550 MB CD-RW as hard disk ? |:o


> I understand that xorriso was meant for writing cd/dvd mediums

Plus Blu-ray. Actually it coordinates ISO 9660 multi-session with writing
to various media and file types.
The boot topic is an add-on, mainly because IBM in ancient times
specified as "El Torito" that booting from CD is an add-on to ISO 9660.


> If a decompressed image of a system takes up 3Gb and you are using an
> 8Gb disk why is it not consistent that you can partition and format the
> rest of it?

Because on the first hand, optical media usually have no partition table
but some have a hardware backed table-of-content which lists tracks and
sessions.

On the second hand, a classical pure-BIOS isohybrid imposes no problem
to partition editors other than often the unusual partition start 0 of
the ISO 9660 partitioni causes a warning. (This can be changed to
block 64 by the xorriso feature of partition ofsset which writes a
second superblock and directory tree for ISO LBA 16 = disk LBA 64.)

On the third hand, Matthew Garrett (mjg) expanded the isohybrid layout
to EFI and even some Macs which expect a HFS+ filesystem with some
special files which are marked by "blessing".
This layout boots on a wide range of machines with x86 processor.
But it offends specifications and the software which more or less
implements those specifications.


> Why would live image makers vary so much in the way they do this?
> I think the vast majority of users are not really interested in the
> details but functionality,

The main functionality is to boot and to offer the installation features.
If the ISO image producers knew how large your USB stick is, then they
could add a partition with empty filesystem which fills up the stick.
But as we see, one may not even believe the size as printed on the
sales box.


Have a nice day :)

Thomas