These are the rules which specify what different concurrent read/write memory accesses from different threads/processes can or cannot see.
Notable such set of rules include:
- C++ memory model. These are also reflected on the semantics of memory of the corresponding instruction set architecture
- SQL transaction isolation level
CIA 2010 covert communication websites noticiasmusica.net by 
Ciro Santilli 35 Updated 2025-04-24 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-04-24 +Created 1970-01-01whoisxmlapi WHOIS record on September 13, 2011
- Registrar Name: NETWORK SOLUTIONS, LLC
- Created Date: February 17, 2010 00:00:00 UTC
- Updated Date: February 17, 2010 00:00:00 UTC
- Expires Date: February 17, 2015 00:00:00 UTC
- Registrant Name: See, Megan|ATTN NOTICIASMUSICA.NET|care of Network Solutions
- Registrant Street: PO Box 459
- Registrant City: PA
- Registrant State/Province: US
- Registrant Postal Code: 18222
- Registrant Country: UNITED STATES
- Administrative Contact
- Administrative Name: See, Megan|ATTN NOTICIASMUSICA.NET|care of Network Solutions
- Administrative Street: PO Box 459
- Administrative City: Drums
- Administrative State/Province: PA
- Administrative Postal Code: 18222
- Administrative Country: UNITED STATES
- Administrative Email: hf3eg77c4nn@networksolutionsprivateregistration.com
- Administrative Phone: 5707088780
- Name Servers: NS45.WORLDNIC.COM|NS46.WORLDNIC.COM
2012:
- Registrant Country: PANAMA
x86 Paging Tutorial 64-bit architectures by Ciro Santilli 35 Updated 2025-04-24 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-04-24 +Created 1970-01-01x86_64 uses 48 bits (256 TiB), and legacy mode's PAE already allows 52-bit addresses (4 PiB). 56-bits is a likely future candidate.
But that would mean that the page directory would have
2^18 = 256K entries, which would take too much RAM: close to a single-level paging for 32 bit architectures!x86_64 uses 4 levels in a
9 | 9 | 9 | 9 scheme, so that the upper level only takes up only 2^9 higher level entries.The 48 bits are split equally into two disjoint parts:
----------------- FFFFFFFF FFFFFFFF
Top half
----------------- FFFF8000 00000000
Not addressable
----------------- 00007FFF FFFFFFFF
Bottom half
----------------- 00000000 00000000A 5-level scheme is emerging in 2016: software.intel.com/sites/default/files/managed/2b/80/5-level_paging_white_paper.pdf which allows 52-bit addresses with 4k pagetables.
Those page faults only happen when a process tries to write to the page, and not read from it.
When Linux forks a process:
- instead of copying all the pages, which is unnecessarily costly, it makes the page tables of the two process point to the same physical address.
- it marks those linear addresses as read-only
- whenever one of the processes tries to write to a page, the makes a copy of the physical memory, and updates the pages of the two process to point to the two different physical addresses
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:
- Video "Anne Wojcicki interview by Talks at Google (2018)" has a few mentions, e.g. youtu.be/pDoALM0q1LA?t=173
- www.theverge.com/2019/12/4/20994361/google-alphabet-larry-page-sergey-brin-sundar-pichai-co-founders-ceo-timeline The rise, disappearance, and retirement of Google co-founders Larry Page and Sergey Brin. Good timeline!
x86 Paging Tutorial Memory management unit by Ciro Santilli 35 Updated 2025-04-24 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-04-24 +Created 1970-01-01Paging is done by the Memory Management Unit (MMU) part of the CPU.
It was later integrated into the CPU, but the term MMU still used.
ELF Hello World Tutorial ELF header by Ciro Santilli 35 Updated 2025-04-24 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-04-24 +Created 1970-01-01Running:outputs:
readelf -h hello_world.oMagic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 64 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 64 (bytes)
Number of section headers: 7
Section header string table index: 3Running:outputs:
readelf -h hello_world.outMagic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: EXEC (Executable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x4000b0
Start of program headers: 64 (bytes into file)
Start of section headers: 272 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 2
Size of section headers: 64 (bytes)
Number of section headers: 6
Section header string table index: 3Bytes in the object file:
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
00000010 01 00 3e 00 01 00 00 00 00 00 00 00 00 00 00 00 |..>.............|
00000020 00 00 00 00 00 00 00 00 40 00 00 00 00 00 00 00 |........@.......|
00000030 00 00 00 00 40 00 00 00 00 00 40 00 07 00 03 00 |....@.....@.....|Executable:
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
00000010 02 00 3e 00 01 00 00 00 b0 00 40 00 00 00 00 00 |..>.......@.....|
00000020 40 00 00 00 00 00 00 00 10 01 00 00 00 00 00 00 |@...............|
00000030 00 00 00 00 40 00 38 00 02 00 40 00 06 00 03 00 |....@.8...@.....|Structure represented:
# define EI_NIDENT 16
typedef struct {
unsigned char e_ident[EI_NIDENT];
Elf64_Half e_type;
Elf64_Half e_machine;
Elf64_Word e_version;
Elf64_Addr e_entry;
Elf64_Off e_phoff;
Elf64_Off e_shoff;
Elf64_Word e_flags;
Elf64_Half e_ehsize;
Elf64_Half e_phentsize;
Elf64_Half e_phnum;
Elf64_Half e_shentsize;
Elf64_Half e_shnum;
Elf64_Half e_shstrndx;
} Elf64_Ehdr;Manual breakdown:
- 0 0:
EI_MAG=7f 45 4c 46=0x7f 'E', 'L', 'F': ELF magic number - 0 4:
EI_CLASS=02=ELFCLASS64: 64 bit elf - 0 5:
EI_DATA=01=ELFDATA2LSB: little endian data - 0 6:
EI_VERSION=01: format version - 0 7:
EI_OSABI(only in 2003 Update) =00=ELFOSABI_NONE: no extensions. - 0 8:
EI_PAD= 8x00: reserved bytes. Must be set to 0. - On the executable it is
02 00forET_EXEC.Another important possibility for the executable isET_DYNfor PIE executables and shared libraries.ET_DYNtells the Linux kernel that the code is position independent, and can loaded at a random memory location with ASLR. - 1 2:
e_machine=3e 00=62=EM_X86_64: AMD64 architecture - 1 4:
e_version=01 00 00 00: must be 1 - 1 8:
e_entry= 8x00: execution address entry point, or 0 if not applicable like for the object file since there is no entry point.On the executable, it isb0 00 40 00 00 00 00 00. The kernel puts the RIP directly on that value when executing. It can be configured by the linker script or-e. But it will segfault if you set it too low: stackoverflow.com/questions/2187484/why-is-the-elf-execution-entry-point-virtual-address-of-the-form-0x80xxxxx-and-n 40 00 00 00on the executable, i.e. it starts immediately after the ELF header.- 2 8:
e_shoff=407x00=0x40: section header table file offset, 0 if not present. The Intel386 architecture defines no flags; so this member contains zero.
- 3 4:
e_ehsize=40 00: size of this elf header. TODO why this field needed? Isn't the size fixed? 38 00on executable: it is 56 bytes long02 00on executable: there are 2 entries.- 3 A:
e_shentsizeande_shnum=40 00 07 00: section header size and number of entries - 3 E:
e_shstrndx(Section Header STRing iNDeX) =03 00: index of the.shstrtabsection.
Pinned article: ourbigbook/introduction-to-the-ourbigbook-project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
Intro to OurBigBook
. Source. We have two killer features:
- topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculusArticles of different users are sorted by upvote within each article page. This feature is a bit like:
- a Wikipedia where each user can have their own version of each article
- a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
Figure 1. Screenshot of the "Derivative" topic page. View it live at: ourbigbook.com/go/topic/derivativeVideo 2. OurBigBook Web topics demo. Source. - local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
- to OurBigBook.com to get awesome multi-user features like topics and likes
- as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
Figure 2. You can publish local OurBigBook lightweight markup files to either OurBigBook.com or as a static website.
Figure 3. Visual Studio Code extension installation.
Figure 5. . You can also edit articles on the Web editor without installing anything locally. Video 3. Edit locally and publish demo. Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension. 
- Infinitely deep tables of contents:
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact