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HOWTO: Be more productive (Aaron Swartz's Raw Thought) on 2008-12-25
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time is "fungible" -- that time spent watching TV can just as easily be spent writing a novel. And sadly, that's just not the case.
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Time has various levels of quality.
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try to make your time higher-quality
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make the best of each kind of time
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Is there something more important you can work on?
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Having a lot of different projects gives you work for different qualities of time
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Integrate the list with your life
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Obviously if you attend one of these, you should stop
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You don't want to overdo it. Sometimes if you're really wasting time you should be distracted.
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ust working on a hard problem with someone else makes it much easier
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Procrastination and the mental force field
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So what causes the mental force field? There appear to be two major factors: whether the task is hard and whether it's assigned.
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A task is a specific concrete step you can take towards your goal.
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The important thing is to have something done right away
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easier to improve something that already exists than to work at a blank page
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how other people did things
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External incentives, like rewards and punishments, kills what psychologists call your "intrinsic motivation" -- your natural interest in the problem.
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it even happens when you try to tell yourself what to do!
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Create a false assignment
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The task has to both seem important (you have to do this to graduate!) and big (hundreds of pages of your best work!) but not actually be so important that putting it off is going to be a disaster.
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Don't assign problems to yourself
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So the secret to getting yourself to do something is not to convince yourself you have to do it, but to convince yourself that it's fun. And if it isn't, then you need to make it fun.
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Another way to make things more fun is to solve the meta-problem.
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identify that component (bring it into awareness), and decide the best way to proceed with it.
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IEEE Spectrum: How We Found the Missing Memristor on 2008-12-24
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had been theorized
nearly 40 years ago,
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In the end, memristors might even become the
cornerstone of new analog circuits that compute using an
architecture much like that of the brain.
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A memristor is a two-terminal device whose
resistance depends on the magnitude and polarity of the
voltage applied to it and the length of time that
voltage has been applied.
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remembers its most recent resistance until
the next time you turn it on
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memristor can be used as
a nonvolatile memory.
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memristors could let us emulate,
instead of merely simulate, networks of neurons and
synapses.
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Memristors can be made extremely small
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It turns out that the influence of
memristance obeys an inverse square law: memristance is
a million times as important at the nanometer scale as
it is at the micrometer scale, and it’s essentially
unobservable at the millimeter scale and larger.
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The crossbar is an array of perpendicular wires.
Anywhere two wires cross, they are connected by a
switch. To connect a horizontal wire to a vertical wire
at any point on the grid, you must close the switch
between them. Our idea was to open and close these
switches by applying voltages to the ends of the wires.
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crossbar architecture builds in redundancy by allowing
you to route around any parts of the circuit that don’t
work.
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One of the major impediments for prior crossbar memory
research was the small off-to-on resistance ratio of the
switches (40 years of research had never produced
anything surpassing a factor of 2 or 3).
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We found the answer in scanning tunneling microscopy
(STM)
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We needed some similar mechanism by which we could
change the effective spacing between two wires in our
crossbar by 0.3 nm.
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Two platinum
electrodes (the intersecting wires of the crossbar
junction) functioned as the “bread” on either end of the
device
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bottom platinum
wire to make an extremely thin layer of platinum
dioxide, which is highly conducting
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film, only one molecule thick, of specially
designed switching molecules. Over this “monolayer”
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titanium metal, which
bonds strongly to the molecules and was intended to glue
them together.
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molecules were supposed to be the actual switches.
We built an enormous number of these devices,
experimenting with a wide variety of exotic molecules
and configurations
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But our fantastic results were inconsistent. Worse yet,
the success or failure of a device never seemed to
depend on the same thing.
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Chua had included a graph that looked
suspiciously similar to the experimental data we were collecting.
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The graph described the current-voltage (I-V)
characteristics that Chua had plotted for his memristor.
Chua had called them “pinched-hysteresis loops”; we
called our I-V characteristics “bow ties.”
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The loop in the I-V curve
is called hysteresis, and this behavior is startlingly
similar to how synapses operate: synaptic connections
between neurons can be made stronger or weaker depending
on the polarity, strength, and length of a chemical or
electrical signal.
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What we had
was not what we had built.
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Under the molecular
layer, instead of platinum dioxide, there was only pure
platinum. Above the molecular layer, instead of
titanium, we found an unexpected and unusual layer of
titanium dioxide. The titanium had sucked the oxygen
right out of the platinum dioxide!
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But closer to
the top platinum electrode, the titanium dioxide was
missing a tiny amount of its oxygen, between 2 and 3
percent. We called this oxygen-deficient titanium
dioxide TiO2-x, where x is about 0.05.
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Because of this misunderstanding, we had been
performing the experiment backward.
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molecule monolayer in the middle of our
sandwich had nothing to do with the actual switching.
Instead, what it did was control the flow of oxygen from
the platinum dioxide into the titanium to produce the
fairly uniform layers of TiO2 and
TiO2-x.
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If a positive voltage is applied to the top
electrode of the device, it will repel the (also
positive) oxygen vacancies in the
TiO2-x layer down into the pure
TiO2 layer. That turns the
TiO2 layer into
TiO2-x and makes it conductive,
thus turning the device on. A negative voltage has the
opposite effect: the vacancies are attracted upward and
back out of the TiO2, and thus
the thickness of the TiO2 layer
increases and the device turns off.
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Memristance arises in a semiconductor when both
electrons and charged dopants are forced to move
simultaneously by applying a voltage to the system.
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take the molecule
monolayers out of our devices
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We needed to find the exact
amounts of titanium and oxygen to get the two layers to
do their respective jobs.
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The resistance of these
devices stayed constant whether we turned off the
voltage or just read their states (interrogating them
with a voltage so small it left the resistance
unchanged).
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In its
initial state, a crossbar memory has only open switches,
and no information is stored. But once you start closing
switches, you can store vast amounts of information
compactly and efficiently. Because memristors remember
their state, they can store data indefinitely,
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the wires and switches
can be made very small: we should eventually get down to
a width of around 4 nm, and then multiple crossbars
could be stacked on top of each other to create a
ridiculously high density of stored bits.
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memristors will never eliminate the
need for transistors: passive devices and circuits
require active devices like transistors to supply
energy.
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Chua’s general memristance definition
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how the
memristor’s voltage depends on current and a “state
variable”
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In Williams’s memristor, the state
variable is the thickness of the stoichiometric
titanium dioxide in the switch; increasing or
decreasing that thickness causes the device’s
resistance to increase or decrease.
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changing
state variable (the TiO2’s
thickness) depends on the amount of charge flowing
through the device.
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Any two crossing wires are connected by a switch
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A positive voltage on the switch
repels the (positive) oxygen deficiencies in the
metallic upper TiO2-x layer,
sending them into the insulating
TiO2 layer below. That causes
the boundary between the two materials to move down,
increasing the percentage of conducting
TiO2-x and thus the
conductivity of the entire switch.
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when the voltage is turned off, positive or
negative, the oxygen bubbles do not migrate. They
stay where they are, which means that the boundary
between the two titanium dioxide layers is frozen.
That is how the memristor “remembers” how much
voltage was last applied.
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IEEE Spectrum: Multicore Is Bad News For Supercomputers on 2008-12-24
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For informatics, more cores doesn’t mean better
performance
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At the heart of the trouble is the so-called memory
wall—the growing disparity between how fast a CPU can
operate on data and how fast it can get the data it
needs.
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In informatics
applications, the problem is worse, explains Richard C.
Murphy, a senior member of the technical staff at
Sandia, because there is no physical relationship
between what a processor may be working on and where the
next set of data it needs may reside.
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The Future of Photography - TIME on 2008-12-22
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The days of darkrooms and negatives are mostly behind us
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film photography lives on in the fine art world
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digital photography as a natural evolution of the form
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The photograph becomes the initial research, an image draft, as vulnerable to modification as it has always been to recontextualization
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[A]mateurs increasingly cover the news more effectively than professionals,
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time for professionals to pay more attention to how amateurs envision the world
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circulating within our bodies
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sudhang on 2008-12-22
okayyyyyyyyy :s
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As each day passes, our view gets richer and more sophisticated thanks to digital technologies
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Paxos - Pinewiki on 2008-12-21
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one of the most efficient practical algorithms for achieving consensus in a message-passing system with
FailureDetectors
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Processes are classified as proposers, accepters, and learners
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So for each proposal, the algorithm proceeds as follows:
- The proposer sends a message prepare(n) to all accepters. (Sending to only a majority of the accepters is enough, assuming they will all respond.)
Each accepter compares n to the highest-numbered proposal for which it has responded to a prepare message. If n is greater, it responds with ack(n, v, nv) where v is the highest-numbered proposal it has accepted and nv is the number of that proposal (or ⊥, 0 if there is no such proposal). (An optimization at this point is to allow the accepter to send back nack(higher number) to let the proposer know that it's doomed and should back off and try again—this keeps a confused proposer who thinks it's the future from locking up the protocol until 2037.)
The proposer waits (possibly forever) to receive ack from a majority of accepters. If any ack contained a value, it sets v to the most recent (in proposal number ordering) value that it received. It then sends accept(n, v) to all accepters (or just a majority). You should think of accept as a command ("Accept!") rather than acquiescence ("I accept")—the accepters still need to choose whether to accept or not.
Upon receiving accept(n, v), an accepter accepts v unless it has already received prepare(n') for some n' > n. If a majority of acceptors accept the value of a given proposal, that value becomes the decision value of the protocol.
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accepter compares n to the highest-numbered proposal for which it has responded to a prepare message
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proposer waits (possibly forever) to receive ack from a majority of accepters
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ack contained a value, it sets v to the most recent (in proposal number ordering) value that it received. It then sends accept(n, v) to all accepters (or just a majority).
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Upon receiving accept(n, v), an accepter accepts v unless it has already received prepare(n') for some n' > n. If a majority of acceptors accept the value of a given proposal, that value becomes the decision value of the protocol.
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Ars Technica Guide to Virtualization: Part I: Page 3 on 2008-12-21
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the VMM must give each guest OS the illusion of exclusive access to the following parts of the machine:
- CPU
- Main memory
- Mass Storage (typically a hard disk)
- I/O (typically a network interface)
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the software presents a carefully crafted and controlled model of the whole computer—called a virtual machine—to each guest OS.
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three primary types of virtualization, each of which is distinguished by the manner in which the VMM interposes itself in between the hardware and the guest OS:
- Emulation (including binary translation)
- Classical virtualization
- Paravirtualization
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software-based model of the entire computer, including the microprocessor. All of the instructions in the instruction streams of both the guest OS and application programs must first pass through the VMM before being passed on to the processor, often so that they can be translated into the processor's native ISA and executed.
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forgo the costly binary translation step and pass the OS and application instruction streams directly on to the processor. The result is that each guest OS and its attendant applications run faster than they would under emulation, but not quite as fast as they would if the OS had exclusive control of the hardware.
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processor traps instructions that might accidentally clue the OS in to the fact that there's something odd and unexpected going on behind its back.
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modifying the guest OS so that these instructions don't pose a problem. With a cooperative guest OS that has been properly modified, the VMM can trust the OS to run with less oversight—and less costly overhead.
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Ars Technica Guide to Virtualization: Part I: Page 2 on 2008-12-21
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There are two main ways that this is accomplished: 1) by running a VMM on top of a host OS, and letting it host multiple virtual machines, or 2) by wedging the VMM between the hardware and the guest OSes, in which case the VMM is called a hypervisor.
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These guest operating systems don't "know" that they're running on top of another software layer. Each one believes that it has the kind of exclusive and privileged access to the hardware that it needs in order to carry out its isolation and arbitration duties. Much of the challenge of virtualization on an x86 platform lies in maintaining this illusion of supreme privilege for each guest OS.
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the hypervisor (also called the virtual machine monitor, or VMM) presents to guest OS a software-created image or simulation of an idealized computer
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called virtual machines (VMs), and the VM is what the OS runs on top of and interacts with.
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as part of a user-level process on a regular OS
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slower than the hypervisor-based approach, since there's much more software sitting between the guest OS and the actual hardware.
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relatively painless to deploy, since you can install them and run them like any other application, without requiring a reboot.
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Server consolidation involves the use of virtualization to replace multiple real but underutilized machines with multiple virtual machines running on a single system.
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saves on space, power, cooling, and maintenance costs.
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live migration, in which an entire virtual machine that's running an OS and application stack is seamlessly moved from one physical server to another, all without any apparent interruption in the OS/application stack's execution.
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By implementing a more robust and coarse-grained form of hardware sharing that swaps entire OS/application stacks on and off the hardware, a VMM can more effectively isolate users and applications from one another for both performance and security reasons.
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Both the Xbox 360 and the Playstation 3 use virtual machines to limit the kinds of software that can be run on the console hardware and to control users' access to protected content
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to write programs for one OS or ISA on another.
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emulation of obsolete hardware, especially older game consoles.
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The Texas Tech Tornado Cluster on 2008-12-19
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About
$1,300
was
spent
on
the
cluster
during
this
period
primarily
on
network
cards
and
hard
drives.
The
emphasis
through
out
the
construction
of
the
Linux
cluster
was
on
low
cost.
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For
teaching
parallel
programming
it¹s
more
important
t
o
first
have
numbers
in
terms
of
cluster
nodes
than
speed
(although
speed
should
not
be
ignored).
Without
numbers,
the
opportunities
to
study
and
learn
about
the
behavior
of
a
multi-computer
cluster
diminishes.
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Ars Technica Guide to Virtualization: Part I: Page 1 on 2008-12-14
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"Vanderpool" that was aimed at providing hardware-level support for something called "virtualization."
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Virtualization implementations are so widespread that some are even popular in the consumer market, and some (the really popular ones) even involve gaming.
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The first of these shifts was the instruction set architecture (ISA) revolution, which was kicked off by IBM's invention of the microcode engine.
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the benefits have less to do with reducing development costs and increasing raw performance than they do with reducing infrastructure costs by allowing software to take better advantage of existing hardware.
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Natasha Demkina - The Girl with Normal Eyes on 2008-11-29
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We wanted a test that would prevent Natasha from making diagnoses that could not be disproved
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required Natasha to find already established medical abnormalities in the test subjects
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Natasha claims to see through people's clothing, yet she says she cannot see through a fabric screen
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Natasha protested during the test that appendixes can grow back after an appendectomy. When told this isn't possible, she insisted that they do grow back in Russia
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Nevertheless, Natasha and her supporters claim she sees what doctors and their tests often miss. The only way I could prove her wrong would be to submit to an autopsy-which I'm not quite ready to do.
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