x86 Paging Tutorial Single level paging scheme numerical translation example Updated 2025-07-16
Suppose that the OS has setup the following page tables for process 1:and for process 2:
entry index entry address page address present
----------- ------------------ ------------ -------
0 CR3_1 + 0 * 4 0x00001 1
1 CR3_1 + 1 * 4 0x00000 1
2 CR3_1 + 2 * 4 0x00003 1
3 CR3_1 + 3 * 4 0
...
2^20-1 CR3_1 + 2^20-1 * 4 0x00005 1entry index entry address page address present
----------- ----------------- ------------ -------
0 CR3_2 + 0 * 4 0x0000A 1
1 CR3_2 + 1 * 4 0x12345 1
2 CR3_2 + 2 * 4 0
3 CR3_2 + 3 * 4 0x00003 1
...
2^20-1 CR3_2 + 2^20-1 * 4 0xFFFFF 1When process 1 tries to access a linear address, this is the physical addresses that will be actually accessed:
linear physical
--------- ---------
00000 001 00001 001
00000 002 00001 002
00000 003 00001 003
00000 FFF 00001 FFF
00001 000 00000 000
00001 001 00000 001
00001 FFF 00000 FFF
00002 000 00003 000
FFFFF 000 00005 000To switch to process 2, the OS simply sets
cr3 to CR3_2, and now the following translations would happen:linear physical
--------- ---------
00000 002 0000A 002
00000 003 0000A 003
00000 FFF 0000A FFF
00001 000 12345 000
00001 001 12345 001
00001 FFF 12345 FFF
00004 000 00003 000
FFFFF 000 FFFFF 000Step-by-step translation for process 1 of logical address
0x00000001 to physical address 0x00001001:- split the linear address into two parts:
| page (20 bits) | offset (12 bits) | - look into Page table 1 because
cr3points to it. - The hardware knows that this entry is located at RAM address
CR3 + 0x00000 * 4 = CR3:
*0x00000because the page part of the logical address is0x00000
*4because that is the fixed size in bytes of every page table entry - since it is present, the access is valid
- by the page table, the location of page number
0x00000is at0x00001 * 4K = 0x00001000. - to find the final physical address we just need to add the offset:
00001 000 + 00000 001 --------- 00001 001because00001is the physical address of the page looked up on the table and001is the offset.The offset is always simply added the physical address of the page. - the hardware then gets the memory at that physical location and puts it in a register.
Another example: for logical address
0x00001001:- the page part is
00001, and the offset part is001 - the hardware knows that its page table entry is located at RAM address:
CR3 + 1 * 4(1because of the page part), and that is where it will look for it - it finds the page address
0x00000there - so the final address is
0x00000 * 4k + 0x001 = 0x00000001
Xah Lee Updated 2025-07-16
fuseki.net/home/List-of-Patreon-Subs-with-Justification.html describes him well:
Homepage xahlee.org/ says:Nice Second brain vibe.
Let's see:
- LinkedIn: www.linkedin.com/in/xahlee/
- youtu.be/a6J62TwOreY?t=271 OMG he also uses a Kinesis Advantage 2 keyboard-like keyboard! Maybe there is something here after all.
- he's also a mad tutorial writer: xahlee.info/Wallpaper_dir/c4_Derivation.html#gc2.2.2.1 like Ciro's Stack Overflow
- www.patreon.com/xahlee £835.2/month from ony 27 members as of 2023, holy crap not bad!
- he was in a bad spot as of 2014: xahlee.info/emacs/misc/xah_as_good_as_dead.htmlThread: www.reddit.com/r/programming/comments/25pypq/im_about_as_good_as_dead_the_end_of_xah_lee/One is reminded of Chill and eat your bread in peace and Quote "Omar Khayyam's chill out quote". xahlee.org/PageTwo_dir/Personal_dir/xah.html autobiography is also of interest.
Yang-Mills existence and mass gap Updated 2025-07-16
- www.youtube.com/watch?v=-_qNKbwM_eE Unsolved: Yang-Mills existence and mass gap by J Knudsen (2019). Gives 10 key points, but the truly hard ones are too quick. He knows the thing though.
Yang-Mills 1 by David Metzler (2011)
Source. A bit disappointing, too high level, with very few nuggests that are not Googleable withing 5 minutes.
Breakdown:
- 1 www.youtube.com/watch?v=j3fsPHnrgLg: too basic
- 2 www.youtube.com/watch?v=br6OxCLyqAI?t=569: mentions groups of Lie type in the context of classification of finite simple groups. Each group has a little diagram.
- 3 youtu.be/1baiIxKKQlQ?list=PL613A31A706529585&t=728 the original example of a local symmetry was general relativity, and that in that context it can be clearly seen that the local symmetry is what causes "forces" to appear
- youtu.be/1baiIxKKQlQ?list=PL613A31A706529585&t=933 local symmetry gives a conserved current. In the case of electromagnetism, this is electrical current. This was the only worthwhile thing he sad to 2021 Ciro. Summarized at: local symmetries of the Lagrangian imply conserved currents.
- 4 youtu.be/5ljKcWm7hoU?list=PL613A31A706529585&t=427 electromagnetism has both a global symmetry (special relativity) but also local symmetry, which leads to the conservation of charge current and forces.lecture 3 properly defines a local symmetry in terms of the context of the lagrangian density, and explains that the conservation of currents there is basically the statement of Noether's theorem in that context.
Year 4 of the physics course of the University of Oxford Updated 2025-07-16
Students choose only one of the Cx courses.
Then there are PhDs corresponding to each of them: www.ox.ac.uk/admissions/graduate/courses/mpls/physics
Zeeman effect Updated 2025-07-16
Non-anomalous: number of splits matches predictions of the Schrödinger equation about the number of possible states with a given angular momentum. TODO does it make numerical predictions?
www.pas.rochester.edu/~blackman/ast104/zeeman-split.html contains the hello world that everyone should know: 2p splits into 3 energy levels, so you see 3 spectral lines from 1s to 2p rather than just one.
It also mentions that polarization effects become visible from this: each line is polarized in a different way. TODO more details as in an experiment to observe this.
Well explained at: Video "Quantum Mechanics 7a - Angular Momentum I by ViaScience (2013)".
Experimental physics - IV: 22 - Zeeman effect by Lehrportal Uni Gottingen (2020)
Source. This one is decent. Uses a cadmium lamp and an etalon on an optical table. They see a more or less clear 3-split in a circular interference pattern,
They filter out all but the transition of interest.
- youtu.be/ZmObNFAqkBE?t=165 passes the lines through a polarizer, which shows how orbital angular momentum is carried by photon polarization
- youtu.be/ZmObNFAqkBE?t=370 says they are looking at 1D2 to 1P1 changes.
ZX-calculus Updated 2025-07-16
As en.wikipedia.org/w/index.php?title=ZX-calculus&oldid=1071329204#Diagram_rewriting tries to explain but fails to deliver as usual consider the GHZ state represented as a quantum circuit.
The naive way would be to just do the matrix multiplication as explained at Section "Quantum computing is just matrix multiplication".
However, ZX-calculus provides a simpler way.
And even more importantly, sometimes it is the only way, because in a real circuit, we would not be able to do the matrix multiplication
This is always possible, because we can describe how to do the conversion simply for any of the Clifford plus T gates, which is a set of universal quantum gates.
Then, after we do this transformation, we can start applying further transformations that simplify the circuit.
It has already been proven that there is no efficient algorithm for this (TODO source, someone said P-sharp complete best case)
But it has been proven in 2017 that any possible equivalence between quantum circuits can be reached by modifying ZX-calculus circuits.
There are only 7 transformation rules that we need, and all others can be derived from those, universality.
So, we can apply those rules to do the transformation shown in Wikipedia:
and one of those rules finally tells us that that last graph means our desired state:because it is a Z spider with and .
Working with PyZX by Aleks Kissinger (2019)
Source. This video appears to give amazing motivation on why you should care about ZX-calculus, it mentions ZynAddSubFX Updated 2025-07-16
Instruments are edited on a GUI. It is a multi-window program, and you open new windows from new windows from new windows, all filled with hundreds of virtual knobs that you drag with your keyboard, and which would be better done from textual software like Csound. It is a thing of beauty.
It does not seem possible to program arbitrary modular synthesizer circuits therefore. But if you understand additive synthesis and subtractive synthesis well, you can make some funky sounds with it.
It is basically a superset of all popular hardware synthesizers ever made.
Has its own built-in MIDI keyboard which is nice.
On Ubuntu 20.04 Version: 3.0.5:as per askubuntu.com/questions/220802/no-sound-zynaddsubfx-and-jack-wont-run/1297988#1297988
To do anything of interest, switch to the Advanced UI:
sudo apt install zynaddsubfx
zynaddsubfx -O alsaTo do anything of interest, switch to the Advanced UI:
- Misc
- Switch Interface Mode
The UI is completely different form what is shown on the website as of 2020: zynaddsubfx.sourceforge.io/, it looks instead like: www.youtube.com/watch?v=iVPr6iUuO3g Maybe on the website it is the new zyn-fusion UI... www.reddit.com/r/linuxaudio/comments/bxn3ur/some_help_for_installing_zynfusion_zynaddsubfx/ so confusing.
And they have some crappy policy of asking for 45 USD for binary downloads.
Compiling from source:fails with:Ciro gives up for now.
git clone https://github.com/zynaddsubfx/zynaddsubfx
cd zynaddsubfx
git checkout a789866de4d45a784c1f4d95fcf5a1938347baef
sudo apt build-dep zynaddsubfx
mkdir build
cd build
cmake ..
make -j`nproc`Traceback (most recent call last):
File "/usr/bin/cxxtestgen", line 7, in <module>
import cxxtest.cxxtestgen
File "/usr/share/cxxtest/cxxtest/__init__.py", line 33, in <module>
from cxxtest.cxxtestgen import *
File "/usr/share/cxxtest/cxxtest/cxxtestgen.py", line 18, in <module>
import __release__
ModuleNotFoundError: No module named '__release__' OurBigBook.com Updated 2025-10-27
The website is the reference instance of OurBigBook Web, which is part of the OurBigBook Project, the other main part of the project are software that users can run locally to publish their content such as the OurBigBook CLI.
The project documentation is present at: docs.ourbigbook.com#ourbigbook-web-user-manual
The topics feature allows you to find the best version of a subject written by other users user
. Live demo: derivative.
OurBigBook's weird specialization towards the weird overly niche interests of its creator Ciro Santilli, notably "I want to create the perfect documentation for every atom in the universe, is undoubtedly partly to blame for the project's failure to gain even a single user outside of its own creator.
However, Ciro does also believe that innovation requires to some degree specializing weirdly in some niche direction. Success comes perhaps from both going into a novel and valuable direction, while still being anatomic enough for enough people.
Asian fetish Updated 2025-10-27
Whenever Ciro's wife starts with "the Asian fetish talk", Ciro reminds her of her own claimed "tall person fetish", and they call it quits.
Asian fetish is much more than sex. It is about the culture, the history, the language. It is the same fetish that makes great mathematicians an Artists do what they do.
When Ciro Santilli was at École Polytechnique, he had to do a presentation for his stupid English courses that all students were forced to take, no matter how good their English was.
The topic was likely something like "pick a country", and Ciro was delighted when he managed to pick "China", after it had gone around a table with many many people before him.
The PowerPoint presentation Ciro made over the weekend was so amazing (and making it was actually fun to make, Ciro actually remembers it a bit!), drawing partly from stuff his wife then girlfriend showed him, that at the end the one of the other students asked him if he had lived in China.
It is a shame Ciro couldn't find the presentation when he wrote this line many many years later. Anything that is not in a BLOB-free monorepo, will disappear, heed my words. But he's certain about two things which it contained:
en.wikipedia.org/wiki/Asian_fetish#History_of_originssubservient, passive, mysterious are understandable. But Hyper-sexual and villainous? OMG have these people never seen real Asians?
en.wikipedia.org/wiki/Asian_fetish#Pornography:
In the United States, women of East and Southeast Asian descent are sometimes stereotyped as subservient, passive, mysterious, villainous in nature, and hyper-sexual.
en.wikipedia.org/wiki/Asian_fetish#Pornography:
Ciro Santilli's sinophily Updated 2025-10-27
Two things come to mind when Ciro Santilli thinks about his sinohpilia.
There is a strong "Ciro Santilli's knowledge hoarding" side to it. Ciro has decided that he has to know EVERYTHING about China. It's culture. It's people. It's art. And so once that has been decided, it becomes inevitable.
But of course, there is also the "which part of Ciro's inner being led to that hoarding decision" part of things. Mishima's quote often comes to mind:
Exoticism is undoubtedly part of it.
Maybe it has something to do with growing up observing 5th+ generation Japanese Brazilians immigrants, well, being Asians and crushing it academically. But also being quiet people, and sometimes misfits. I.e., nerds.
Maybe there is also something to do with the influence Japanese anime, highly popular during Ciro's childhood in Brazil. Ciro, unlike many of his friends, left that relatively early, as he got into the deeper pleasures of natural sciences and then more traditional Asian culture. But still.
And finally perhaps the correlation between sofware engineers and Asian fetish and the correlation between software engineers and Buddhism.
Fluid mechanics Updated 2025-10-27
Boooooring. Except for Navier-Stokes existence and smoothness. That's OK.
Navier-Stokes existence and smoothness Updated 2025-10-27
A report on the Navier-Stokes Problem by Vladimir Šverak
. Source. 2025. The eye in Ciro Santilli's website banner Updated 2025-11-18
Ciro was trying to make his face fit on the banner. But it is hard because faces are square and text is long.
At this moment, Ciro knew what to do.
Finally, by adding another eye to the footer of the page, this also added a symbolic dimension to things: the pages contain what is in between Ciro's eyes: his brain: Section "Braindumping".
The concept, like any other, is not in itself new and has been used by others, Ciro just independently rediscovered it again:
Synthetic virus Updated 2025-11-18
Man-made virus!
TODO: if we had cheap de novo DNA synthesis, how hard would it be to bootstrap a virus culture from that? github.com/cirosantilli/cirosantilli.github.io/issues/60
Is it easy to transfect a cell with the synthesized DNA, and get it to generate full infectious viral particles?
If so, then de novo DNA synthesis would be very similar to 3D printed guns: en.wikipedia.org/wiki/3D_printed_firearms.
It might already be possible to order dissimulated sequences online:
List of subtitle file formats Updated 2025-11-18
Ciro Santilli's hardware Internet speed Updated 2025-11-18
Home 2017 TalkTalk 38Mbps nominal, Google M-lab speed test:
- 36.4 Mbps download
- 9.15 Mbps up
- 58 ms latency over 80km of first world
Home 2025 Giffgaff
Home 2025 Sky Broadband WiFi Max Hub SR213 (SR213-02-UK-wht) 1GBPS:Admin at 192.168.0.1/ username admin password same as wifi password.
- Lenovo ThinkPad P14s gen4 amd
- wired to fiber box:
- wireless sitting next to router:
- Google Pixel 7a
- wireless sitting next to router: 414 down 107 up. Receiver bound which is funny.
Inscription (blockchain) Updated 2025-11-18
Data that is inscribed in a blockchain as a way to perpetuate the data, rather than to follow the main intended purpose of the given blockchain, e.g. ASCII art instead of financial transactions on the Bitcoin blockchain.
Uncanny valley Updated 2025-11-05
Side project time Updated 2025-11-05
Rotate object around a point in Inkscape Updated 2025-11-05
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