
Turn your PC upside down to boot into Linux (2003) - PascLeRasc
http://www.mini-itx.com/projects/windowsxpbox/?page=4
======
lorenzhs
High-end laptops like ThinkPads often have an accelerometer, I'm not quite
sure how hard it would be to access it from GRUB2 but it would definitely be a
neat trick to boot a hidden partition or something. Or maybe display a fake
error message and refuse to boot if it's _not_ sideways as a crude method of
protection.

~~~
jsingleton
Many laptops have these sensors, often as part of a hard drive protection
system. If it detects 9.8g suddenly going to 0g then it parks the read head as
it's probably just been dropped. I'm not sure if they're still present in this
era of SSDs. Maybe if they weren't part of the disk itself.

They were used by the Quake-Catcher Network project from Stanford. Although
from the OS.

    
    
      ...seismic network by utilizing sensors in and attached to internet-connected computers.
    

[https://github.com/carlgt1/qcn](https://github.com/carlgt1/qcn)

Edit: Yes, I meant ms⁻² not g. Been a while since I've done any physics. 9.8g
is probably more like what it would sense when hitting the floor, which is a
bit too late to do anything useful. At least I didn't claim it to be
6.54×10⁻¹⁰ Nm²kg⁻² (bonus points if you get this).

~~~
delazeur
> If it detects 9.8g suddenly going to 0g then it parks the read head as it's
> probably just been dropped.

9.8g? Is your office inside a centrifuge? :-P

~~~
knodi123
9.8g is actually a perfectly reasonable _deceleration_ value at time of
impact. So if it detects 9.8g followed by 0g, it's likely that it has bounced!

~~~
semi-extrinsic
It would have to be followed by 1g, not 0g. Unless the laptop bounced in
space.

~~~
nitrogen
The accelerometer on a laptop on a ballistic trajectory should still read 0,
shouldn't it?

~~~
semi-extrinsic
Ah, sorry. Yes, it will, because a typical accelerometer measures not the
acceleration, but _the deviation in acceleration from freefall_. So it will
show an acceleration of 1g when standing on a table, and 0g in freefall.

Which is obviously wrong if you think of it as measuring the acceleration of
the laptop. The physical acceleration of the laptop is obviously zero when it
is at rest on a table. (Acceleration is the change in speed, and the laptop
has zero change in speed.)

~~~
theoh
Can you build a consistent accelerometer that does what you want?

If you think about the accelerometer as a little micromechanical arm which is
being deflected relative to the laptop by the force of gravity, it makes a lot
more sense. When they're falling together the deflection is 0.

~~~
semi-extrinsic
> Can you build a consistent accelerometer that does what you want?

I gave it some thought, and no, I don't think you can build a self-contained
one. But if you allow external communications it becomes very doable (see: GPS
system). Also, if you allow another input that tells the device it's
orientation wrt. the gravitational field, say a magnetic field sensor, it
becomes easy.

~~~
theoh
If your accelerometer measures what Wikipedia calls "coordinate acceleration"
it's something observer relative so I expect (waves hands) "problems" will
arise with measuring in relation to your chosen reference frame at
relativistic speeds.

------
ksherlock
Cute trick. Reminds me of the Karateka easter egg -- if you inserted the
floppy disk upside down[1], the graphics displayed upside down.

1\. 95% of HN is now confused

~~~
dordoka
For those interesed, I was among the not-confused-but-curious (I'm old enough
to even have inserted cassette tapes on a computer) and found out this [0]
explanation :) Nice story, thanks ksherlock.

[0]: [http://www.geek.com/games/karateka-apple-ii-floppy-disk-
had-...](http://www.geek.com/games/karateka-apple-ii-floppy-disk-had-a-side-b-
played-game-upside-down-1509335/)

~~~
speeder
Unfortunately it is not explained HOW they did it.

It is somewhere on Mechner site and diaries, but I can't find it again.

Basically, one day while coding, he found out that one single bit caused a bug
in rendering that flipped the whole game upside down, it was completely
unintentional.

But he thought it would be hilarious to make the easter egg (indeed, it was).

Later he used the same technique on Prince of Persia game (there is an area of
the game where you drink a potion that flips that bit, flipping the whole game
upset down, this had to be emulated for non-Apple systems, probably caused
some pain to people porting the game :P)

~~~
wang_li
The Apple II floppy drives were single sided. It would be trivial to put
different code on the other side of the floppy disk itself.

A single bit error that would simply flip everything upside down seems quite
improbable given the Apple II hardware. I wouldn't be surprised if a bug
inspired the easter egg, but I'd be shocked if there was a single bit
difference between the front and back of the floppy.

~~~
speeder
I think it was related to something about how a pointer to the video data
worked in the game engine (not a property of Apple II itself).

Maybe it was the positive/negative bit that was flipped, and made the pointer
read backwards and underflow, but end rendering anyway due to some hardware
quirk.

~~~
wang_li
I don't believe that the 6502 had such a thing as a positive/negative bit that
would have this kind of effect.

On that hardware, if I was going to do this, I'd just reverse the order of the
entries in the scanline lookup table. On the Apple II the address of the first
pixel of each scanline did not follow immediately after the address of the
last pixel of the prior scanline. So every program that did any graphics work
used a lookup table to get the address of a particular scanline.

As long as you were consistent in your use of this table, that would be the
only necessary change to flip the game upside down.

~~~
apricot
Reversing the scanline lookup table is indeed how it was done.

Source: I disassembled it, a long time ago.

------
SFjulie1
[http://www.linux.sh/loadlin.html](http://www.linux.sh/loadlin.html)

in 2003 you still could install linux on a FAT32 system and boot from windows,
you could even share your swap space with the file windows was using for the
same purpose.

So an autoexec.bat with a menu and loadlin called in the process. It was not
even a big penalty.

We were real hackers like this :
[http://www.tsgk.net/cowboyz/tdc.html](http://www.tsgk.net/cowboyz/tdc.html)

------
rdl
Software delivered in large physical boxes; not so much nostalgia but horror
at 1) how wasteful the process was 2) how skewed it made things -- not being
able to easily patch and thus deathmarch or even late shipping, and then the
horrors of shipping crap and then hoping the patch would fix it, because you
had to ship on a specific date.

And just how hard to make/expensive/etc. boxes, manuals, etc. were, and how
annoying it was to manage inventory.

~~~
gh02t
I can remember when PC game boxes shrunk down from the huge size to the
smaller format. And now they are "shrinking" into nothingness with digital
distribution.

~~~
ge0rg
Yes, and the games you "buy" also shrink into nothingness if the distributor
goes bankrupt or you are accused to violate somebody's ToS. I wish back for
the physical distribution of game media and offline validation of serial
numbers, if only to be able to play my old games in 20 years.

~~~
gh02t
True, though half the time nowadays all the physical copy does is link to a
download. The last game I can remember buying a physical copy of was Civ V and
basically the only thing in the box was a link to download it on Steam. With
the onerous always-on DRM that seems so prevalent in many games today I'm not
optimistic that I'll be able to play many of the more recent games I "own" in
20 years anyway.

~~~
jhasse
There are recent games which go against this trend. For example the last one I
bought without DRM was Divinity: Original Sin Enhanced Edition. Support them
:)

~~~
gh02t
I did :)

------
noonespecial
Shake it upside-down to reboot would be much more fun.

~~~
ChuckMcM
An oldie but a goodie :
[http://dilbert.com/strip/1995-04-03](http://dilbert.com/strip/1995-04-03)

~~~
noonespecial
Thanks. That's the one I was thinking of but for some reason I was remembering
it as having been a "User Friendly" so my google-fu failed me.

------
golergka
> Greetings Hackaday visitors and Time Travellers from the early 2000s!

This is the best reaction I have ever seen to a sudden surge of traffic to an
old page.

~~~
PascLeRasc
Yeah I posted this on Sunday and it seems to just have taken off this morning
- is that normal?

~~~
dang
dikaiosune has it right. We put it in the second-chance pool, described at
[https://news.ycombinator.com/item?id=10705926](https://news.ycombinator.com/item?id=10705926)
and earlier posts linked from there. It's the latest in a long series of
experiments to try to give good stories a second crack at the front page.

Edit: Wow, you've been posting some great articles:
[https://news.ycombinator.com/submitted?id=PascLeRasc](https://news.ycombinator.com/submitted?id=PascLeRasc).
We've put
[https://news.ycombinator.com/item?id=11007792](https://news.ycombinator.com/item?id=11007792)
in the second-chance pool and we'll send you a repost invite for
[https://news.ycombinator.com/item?id=10932621](https://news.ycombinator.com/item?id=10932621).
(After a few days have gone by, we do the latter instead of re-upping the
post.) Hope you'll keep up the great submissions!

~~~
PascLeRasc
Wow, thanks! I'm glad my posts are appreciated.

~~~
dang
We're suckers for high-quality historical material that hasn't appeared here
before. HN can never have enough of that.

------
larrydag
Perhaps I'm missing the point. If one is going to boot up between OS's that
often wouldn't virtualization work best? Other than that it is a neat hack.

~~~
KC8ZKF
The points you are missing are 2003 and Celeron. Efficient and easy
virtualization is relatively recent.

~~~
thrownaway2424
VMWare Workstation was already on its 4th major release by 2003.

~~~
dsp1234
Hardware virtualization for intel/amd processors did not come until 2006. So
you could run VMWare and get decent performance with paravirtualized drivers,
but running a completely different OS would have required software
virtualization, and it was not fast by any means. Booting to the other
operating system was a much better experience since the OS would then have
full use of the resources without software virtualization being in the way.

~~~
wang_li
Software only virtualization was faster than the first generation of hardware
supported virtualization.

See page 7. of this document:
[http://www.vmware.com/pdf/asplos235_adams.pdf](http://www.vmware.com/pdf/asplos235_adams.pdf)

~~~
thrownaway2424
Indeed. It is quite amazing how history is being revised here. Software
virtualization was extremely useful from day 1.

