Tweedledum is a first-generation iMac (233 MHz
slot-loading, 192Mb RAM, No Airport) whereas Tweedledee is
2nd-generation (350 MHz front-loading, 192Mb RAM, Airport card). A
couple of weeks ago I replaced their original hard-discs (4 Gb resp. 6
Gb) by fat 120 Gb discs and from this weekend they serve as our
backup-facility. Tweedledee is connected via Airport to our network and
is a fully functional 10.3 computer, everyone has a login on it and is
encouraged to dump important files onto it as a secondary copy.
Tweedledum. on the other hand, is invisible to the network but forms a
one-wire network with Tweedledee (they are connected by a crossed
ethernet cable which results in having a self-assigned IP address in the
169.254 range and hence they can see each other; moreover using the
Sharing-pane in the System Preferences I allowed
Tweedledee to share its internet connection to other computers,
connected to it via Ethernet, so Tweedledum can go online to get
system-updates when necessary).
A house-computer rule is that
all important files (which means those you don’t like to loose in a
crash) are kept in the Documents folder of your
Home-folder on your own computer. At regular intervals I make
sure that these folders are synchronized with backup-copies on both
Tweedledee & Tweedledum, so at any given time there are at least 3
computers containing the essential files (usually more as everyone has a
login at each of the 4 ‘work’-computers and can drop extra copies
around, but must clean-up when asked).
To synchronise I use
the shareware program ExecutiveSync. It is no longer possible to
obtain this from its original homepage as they seem to have been taken
over and invite you to buy You Sinc instead which costs more than
twice what ExecutiveSync costs (19.95$). Fortunately, for now you can
still download it from the Apple site. I have
ExecutiveSync running on Tweedledee (you are only allowed to run it on
one computer, you can install it on every computer but then the
synchronizing process is sometimes not possible which is why I came to
the following work-around). In ExecutiveSync you make several
Projects which involve choosing a Local folder and a
Remote folder somewhere on your network which you want to keep in
Sync. In my Home folder on Tweedledee I made several (originally
empty) folders such as docsGitte. Then my ExecutiveSync-project
syncGitte takes docsGitte as the local folder and the
/Users/gitte/Documents-folder on iBookGitte as the remote
folder. The first time you synchronise takes a lot of time (especially
over the wireless network, it may be better to do the first sync via
ethernet) but afterwards it works pleasantly.
Once I
synchronised all the local Documents-folders with the corresponding
folders in my home-folder on Tweedledee, I have another
ExecutiveSync-project BACKUP which takes as the Local-folder my
Home-folder and as the remote folder a folder BACKUP I did create
on Tweedledum. Fortunately, here the synchronising is done over Ethernet
or it would take forever.
neverendingbooks Posts
Today I
did prepare my lectures for tomorrow for the NOG master-class on
non-commutative geometry. I\’m still doubting whether it is worth TeXing
my handwritten notes. Anyway, here is what I will cover tomorrow :
– Examples of l-algebras (btw. l is an
arbitrary field) : matrix-algebras, group-algebras lG of finite
groups, polynomial algebras, free and tensor-algebras, path algebras
lQ of a finite quiver, coordinaterings O(C) of affine smooth
curves C etc.
– Refresher on homological algebra : free and
projective modules, exact sequences and complexes, Hom and Ext groups
and how to calculate them from projective resolutions, interpretation of
Ext^1 via (non-split) short exact sequences and stuff like that.
– Hochschild cohomology and noncommutative differential forms.
Bimodules and their Hochschild cohomology, standard complex and
connection with differential forms, universal bimodule of derivations
etc.
– Non-commutative manifolds. Interpretation of low degree
Hochschild cohomology, characterization of non-commutative points as
separable l-algebras and examples. Formally smooth algebras
(non-commutative curves) characterised by the lifting property for
square-free extensions and a proof that formally smooth algebras are
hereditary.
Next week I will cover the representation
varieties of formally smooth algebras and the semigroup on their
connected (or irreducible) components.
This
week I reread with pleasure all 918 pages of Cryptonomicon by Neal Stephenson and found out
that last time I had been extremely choosy in subplots. There are 4
major plots : one contemporary (a couple of geeks trying to set up a data-haven) and three
WW2 stories : the Waterhouse-plot about cracking Enigma and other
crypto-systems featuring a.o. Alan Turing, the Shaftoe-plot about the
crazy division 2702 trying to cover-up that Enigma has been broken and
the Goto Dengo-plot about hiding the Japanese Gold reserve in the
jungle. Five years ago I was mostly interested in the first two subplots
and later on in the book I jumped chapters quite a bit, it seems.
During the first read I assumed that the Van Eck
phreaking-bit was just another paranoid misconception of the two present
day main players Randy&Avi, but this week I wasn\’t so sure anymore so
the first thing I did when we came home was Googling on Van Eck phreaking which really does
exist!
Van Eck phreaking is a form of eavesdropping in which
special equipment is used to pick up telecommunication signals or data
within a computer device by monitoring and picking up the
electromagnetic fields.
The U.S. government has been involved
with EM interpretation for many years under a top-secret program
code-named “TEMPEST”.
It seems that in 1985 the
Dutch scientist Wim Van Eck wrote a paper \’Electromagnetic Radiation from Video Display Units:
An Eavesdropping Risk?\’ He concluded: “If no preventive measures
are taken, eavesdropping on a video-display unit is possible at several
hundred meters distance, using only a normal black-and-white TV
receiver, a directional antenna, and an antenna amplifier.” He proved
it by taking a BBC crew around London in a van, showing them what was on
the computer screens at various companies.
To me it seems that
putting your computer inside a Faraday cage is a simpler counter-measure than
the cumbersome method of Randy in the novel (but I have to admit, he
was in prison at the time…). There is a more detailed manual on
phreaking available, but the best text I found (sofar) on Van Eck
phreaking is Soft Tempest: Hidden Data Transmission Using
Electromagnetic Emanations by Markus G. Kuhn and Ross J.
Anderson.