Ciro Santilli @cirosantilli 37

The fundamental insight of Git design is: a SHA represents not only current state, but also the full history due to the Merkle tree implementation, see notably:

This makes it so that you will always notice if you are overwriting history on the remote, even if you are developing from two separate local computers (or more commonly, two people in two different local computers) and therefore will never lose any work accidentally.

It is very hard to achieve that without the Merkle tree.

Consider for example the most naive approach possible of marking versions with consecutive numbers:

If Local 1 were to push to Remote first, how could Local 2 notice that when it tries to push itself? The navie method of just checking: "does Remote have commit "2"" does not work, because Local 2 has a different version of commit 2 than local 1.

Street View's go into the past mode is the dream of every archaeologist. Ciro can only dream of a magic street view that allows going back to earlier centuries and beyond... isn't it amazing to think that people in the future will have that ability to time travel back to around the year 2006? Ciro wonders how long Google will be able to keep storing data like that.

Thanks, CIA.

The 1997 Wayback Machine archives are just priceless: web.archive.org/web/19971210065425/http://backrub.stanford.edu/backrub.html. I'm so glad that website exists and started so early. It is just another university research project demo website like any other. Priceless.

Craig Silverstein was the first employee hired, in 1998: www.newyorker.com/magazine/2018/12/10/the-friendship-that-made-google-huge

In August 1998 they had an their first investment of $100,000 from Andy Bechtolsheim, Sun Microsystems co-founder. Some sources say September 1998. This was an event of legend, the dude dropped by, tested the website for a few minutes, said I like it, and dropped a 100$ check with no paperwork. Google wasn't even incorporated, they had to incorporate to cash the check. They were apparently introduced by one of the teachers, TODO which. Some sources say he had to rush off to another meeting afterwards:

Tried to sell it for 1 million in early 1999... OMG the way the world is. It would be good to learn more about that story, and when they noticed it was fuckup.

One of Google's most interesting stories is how their startup garage owner became an important figure inside Google, and how Sergei married her sister. These were the best garage tenants ever!

Bibliography:

Basically a GUI music editor where you can specifically see and export classical music notation instead of tablature-style notation.

Best open source one found so far as of 2020: MuseScore.

Perfect Git integration belongs in integrated development environments :-)

This section is about the male/female trait.

For the act, see: sex.

Theory that atoms exist, i.e. matter is not continuous.

Much before atoms were thought to be "experimentally real", chemists from the 19th century already used "conceptual atoms" as units for the proportions observed in macroscopic chemical reactions, e.g. $2H_2+O_2\leftrightarrow H_{2}O$. The thing is, there was still the possibility that those proportions were made up of something continuous that for some reason could only combine in the given proportions, so the atoms could only be strictly consider calculatory devices pending further evidence.

Subtle is the Lord by Abraham Pais (1982) chapter 5 "The reality of molecules" has some good mentions. Notably, physicists generally came to believe in atoms earlier than chemists, because the phenomena they were most interested in, e.g. pressure in the ideal gas law, and then Maxwell-Boltzmann statistics just scream atoms more loudly than chemical reactions, as they saw that these phenomena could be explained to some degree by traditional mechanics of little balls.

Confusion around the probabilistic nature of the second law of thermodynamics was also used as a physical counterargument by some. Pais mentions that Wilhelm Ostwald notably argued that the time reversibility of classical mechanics + the second law being a fundamental law of physics (and not just probabilistic, which is the correct hypothesis as we now understand) must imply that atoms are not classic billiard balls, otherwise the second law could be broken.

Pais also mentions that a big "chemical" breakthrough was isomers suggest that atoms exist.

Very direct evidence evidence:

Less direct evidence:

Subtle is the Lord by Abraham Pais (1982) page 40 mentions several methods that Einstein used to "prove" that atoms were real. Perhaps the greatest argument of all is that several unrelated methods give the same estimates of atom size/mass:

Why are pages 4 KiB anyways?

There is a trade-off between memory wasted in:

This can be seen with the extreme cases:

x86 designers have found that 4 KiB pages are a good middle ground.

The exact format of table entries is fixed by the hardware.

Each page entry can be seen as a struct with many fields.

The page table is then an array of struct.

On this simplified example, the page table entries contain only two fields:so in this example the hardware designers could have chosen the size of the page table to b 21 instead of 32 as we've used so far.

All real page table entries have other fields, notably fields to set pages to read-only for Copy-on-write. This will be explained elsewhere.

It would be impractical to align things at 21 bits since memory is addressable by bytes and not bits. Therefore, even in only 21 bits are needed in this case, hardware designers would probably choose 32 to make access faster, and just reserve bits the remaining bits for later usage. The actual value on x86 is 32 bits.

Here is a screenshot from the Intel manual image "Formats of CR3 and Paging-Structure Entries with 32-Bit Paging" showing the structure of a page table in all its glory: Figure 1. "x86 page entry format".

The fields are explained in the manual just after.