On 7/20/2012 10:31, Le_Forgeron wrote:
> Nowadays (and since most 1GB hard drive... quite old), its not possible
> anymore. Writing 0 or random number is the same: the old data is not
> recoverable.

This. Plus, if it's an SSD or has flash backup, you can write it all you 
want and unless you rewrite the entire drive multiple times, you're not 
guaranteed to get rid of the junk.

-- 
Darren New, San Diego CA, USA (PST)
   "Oh no! We're out of code juice!"
   "Don't panic. There's beans and filters
    in the cabinet."

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On 7/20/2012 13:22, clipka wrote:
> Am 20.07.2012 20:54, schrieb Le_Forgeron:
>> Le 20/07/2012 19:46, clipka nous fit lire :
>>>
>>> Quiz: If you had highly sensitive data on your hard drive, and needed to
>>> erase it for sure - would you rather trust this alleged fact, or have
>>> the erasing software write random numbers just in case?
>>
>> If the data on drive was so sensitive, I would use chemistry first. Then
>> a bit of heavy hammer physic, and finally a good heat with partial
>> ionisation, at temperature far above the curie point.
>>
>> Boiling HCl is probably enough, as a starter. (get ride of most iron &
>> steel). Wear a protective mask and operate under well vented condition.
>
> Not recommended if you want to continue to use the hard drive though.

If it's not sensitive enough to pay to replace the drive, it's not sensitive 
enough to worry about whether you're erased with zeros or with random data.

-- 
Darren New, San Diego CA, USA (PST)
   "Oh no! We're out of code juice!"
   "Don't panic. There's beans and filters
    in the cabinet."

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On 7/20/2012 2:58, Le_Forgeron wrote:
> HT is: a second set of registers. Nothing more. No additional FPU or
> fancy integer units.

This. Generally, the second core runs during cache misses of the first core. 
The design intent was to help alleviate the problem of having main memory 
RAM much slower than CPUs.

-- 
Darren New, San Diego CA, USA (PST)
   "Oh no! We're out of code juice!"
   "Don't panic. There's beans and filters
    in the cabinet."

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On 20/07/2012 09:31 PM, Darren New wrote:
> On 7/20/2012 2:58, Le_Forgeron wrote:
>> HT is: a second set of registers. Nothing more. No additional FPU or
>> fancy integer units.
>
> This. Generally, the second core runs during cache misses of the first
> core. The design intent was to help alleviate the problem of having main
> memory RAM much slower than CPUs.

Really? I thought the design intent was to utilise idle execution units 
if a particular thread is hammering (say) only integer units, leaving 
the float units idle.

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Le 20/07/2012 23:07, Orchid Win7 v1 nous fit lire :
> On 20/07/2012 09:31 PM, Darren New wrote:
>> On 7/20/2012 2:58, Le_Forgeron wrote:
>>> HT is: a second set of registers. Nothing more. No additional FPU or
>>> fancy integer units.
>>
>> This. Generally, the second core runs during cache misses of the first
>> core. The design intent was to help alleviate the problem of having main
>> memory RAM much slower than CPUs.
> 
> Really? I thought the design intent was to utilise idle execution units
> if a particular thread is hammering (say) only integer units, leaving
> the float units idle.

The "hammering" is no more: a single instruction is split in multiple
different steps, each using different parts. Each step take some cycles,
and some steps could be very long when compared to another.
Hence the possible reordering inside the pipeline, which was a bit
before they think of HT.

Take the instruction decoder: it ends up doing nothing while the FPU is
doing your division. Well... when the division is actually performed at
the FPU, the decoder is actually decoding the fourth or fifth
instruction after the division. Yet, bubbles of empty cycles happen on
the pipeline: your division was followed by an unrelated addition of two
integers... that addition took far less cycles than the division, so
instructions #2,#3,#4 and #5 have already been performed when #1 is
still running. Yet, result of#1 is now needed... and we have all these
decoder, ALU and all which are idle... Let's have a second thread of
execution, absolutely unrelated because it run another piece of code.
All we need is a second set of registers (dedicated) and some circuitry
to use the idle cycles of every sub-parts. (sound easy, it's a bit complex).

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On 7/20/2012 12:46 PM, clipka wrote:

> Quiz: If you had highly sensitive data on your hard drive, and needed to
> erase it for sure - would you rather trust this alleged fact, or have
> the erasing software write random numbers just in case?

Why are you disposing of a drive that still works?  In every 
organization I've worked for, especially the military ones with scads of 
sensitive information to manage, a drive was kept (and used) for as long 
as it was operational.  We simply couldn't afford to let one go if it 
was still useful.

For most people, the only sensitive information on their drives is the 
passwords to their on-line activities.  You protect those by changing them.

Regards,
John

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Le 2012-07-21 11:58, John VanSickle a écrit :
> On 7/20/2012 12:46 PM, clipka wrote:
>
>> Quiz: If you had highly sensitive data on your hard drive, and needed to
>> erase it for sure - would you rather trust this alleged fact, or have
>> the erasing software write random numbers just in case?
>
> Why are you disposing of a drive that still works?  In every
> organization I've worked for, especially the military ones with scads of
> sensitive information to manage, a drive was kept (and used) for as long
> as it was operational.  We simply couldn't afford to let one go if it
> was still useful.

This branching off the original topic was the need of my employer to put 
the OS swapfile on an encrypted partition to prevent data leakage in 
case of theft.

Why do thiefs get rid of working disks?  Because they do not have any 
need for them once they have gathered the information that was on them.

> For most people, the only sensitive information on their drives is the
> passwords to their on-line activities.  You protect those by changing them.

The company directive mentioned above is not for "most people", but for 
people who happen to have confidential material on their work laptops.

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> If the data on drive was so sensitive, I would use chemistry first. Then
> a bit of heavy hammer physic, and finally a good heat with partial
> ionisation, at temperature far above the curie point.
>
> Boiling HCl is probably enough, as a starter. (get ride of most iron&
> steel). Wear a protective mask and operate under well vented condition.

I'm not so sure acid would actually work. You're assuming that the layer 
of iron is at the surface; this is not necessarily the case. It may well 
have a layer of lacquer on top.

Also, you would /think/ that soaking plastic in a wide range of 
hydrocarbon solvents would destroy it. But having personally tried it 
with almost the entire contents of our lab's reagent cupboards, I can 
confirm that this is not the case at all. Similarly, mineral acids are 
probably not the flesh-eating monsters we all see on TV.

I have also discovered that most drives seem to have platters made of 
glass. It's really very, very easy to shatter these, requiring no 
specialist equipment at all. (Beyond some way of undoing the screws. 
They quite often require unusual drivers... A drill sometimes does the 
job though.)

The Curie point of pure iron is 770°C. My oven only goes up to 250°C. 
(This is probably related to the fact that my oven is *made of* iron!) 
You would need some kind of industrial kiln.

The melting point of glass varies by type. Borosilicate glass melts at 
"only" 800°C, but most types melt at well over 1,00°C. (The median 
temperature is listed as 1,700°C.) Good luck finding an oven that hot!

Really, unless you work for the DOD, a software wipe with /any/ data 
pattern, followed by some gentle prodding with a hammer is quite sufficient.

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Le 23/07/2012 10:05, Invisible a écrit :
>> If the data on drive was so sensitive, I would use chemistry first. Then
>> a bit of heavy hammer physic, and finally a good heat with partial
>> ionisation, at temperature far above the curie point.
>>
>> Boiling HCl is probably enough, as a starter. (get ride of most iron&
>> steel). Wear a protective mask and operate under well vented condition.
> 
> I'm not so sure acid would actually work. You're assuming that the layer
> of iron is at the surface; this is not necessarily the case. It may well
> have a layer of lacquer on top.
> 
> Also, you would /think/ that soaking plastic in a wide range of
> hydrocarbon solvents would destroy it. But having personally tried it
> with almost the entire contents of our lab's reagent cupboards, I can
> confirm that this is not the case at all. Similarly, mineral acids are
> probably not the flesh-eating monsters we all see on TV.

I had first hand experience (now more than 25 years ago) with *boiling*
HCl. It really eats iron (but not as speedy as shown on TV).

Main interest of HCl, expecially boiling: its huge oxydation capacity.
Nearly all metals are going into solution with enough time (gold,
platine and a few would need to play with regal water (which means
getting some nitric acid... that one is difficult to find as free use
(regulated as components for making explosives))

You do not have to open the disc: put the whole boxed disc inside the
boiling acid and let it work. The metal goes away (including a clean
PCB: no more tracks...)
The engines are deleted as well, and the springs, and the heads...

> 
> I have also discovered that most drives seem to have platters made of
> glass. It's really very, very easy to shatter these, requiring no
> specialist equipment at all. (Beyond some way of undoing the screws.
> They quite often require unusual drivers... A drill sometimes does the
> job though.)

Platters are made of glass since 2003, IIRC. Yet, a shattered platter
could be readable by the alien technology, so better rinse them first
and get ride of the magnetic coverage.

Why drill when the acid is there for you. The crew are gone, the casing
is gone...
Put the drive in the acid in the morning, plenty of time to read the
comics while the drive get destroyed: profit!

> 
> The Curie point of pure iron is 770°C. My oven only goes up to 250°C.
> (This is probably related to the fact that my oven is *made of* iron!)
> You would need some kind of industrial kiln.

The "ionisation" was to be done with some plasma torch, or alike.
Just check the plasma temperature vs the curie point.

At worst, acetylen+oxygen is high enough for that (3200°C) and not a
problem to get a hand on (usual welding).

> 
> The melting point of glass varies by type. Borosilicate glass melts at
> "only" 800°C, but most types melt at well over 1,00°C. (The median
> temperature is listed as 1,700°C.) Good luck finding an oven that hot!
> 
> Really, unless you work for the DOD, a software wipe with /any/ data
> pattern, followed by some gentle prodding with a hammer is quite
> sufficient.

DOD has its own procedure. And they can provide the equipment.

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On 23/07/2012 12:50 PM, Le_Forgeron wrote:

> You do not have to open the disc: put the whole boxed disc inside the
> boiling acid and let it work. The metal goes away (including a clean
> PCB: no more tracks...)
> The engines are deleted as well, and the springs, and the heads...

We actually /have/ a fume cupboard in the lab. And several litres of 
laboratory-grade hydrochloric acid. And a heater.

Holy cow, you probably should not have told me about this...   ._.

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