Graduate course of the University of Oxford by 
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01 Classification of 4-transitive groups by Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01en.wikipedia.org/w/index.php?title=Mathieu_group&oldid=1034060469#Multiply_transitive_groups is a nice characterization of 4 of the Mathieu groups.
The lab that made Chicago Pile-1, located in the University of Chicago. Metallurgical in this context basically as in "working with the metals uranium and plutonium".
Given their experience, they also designed the important X-10 Graphite Reactor and the B Reactor which were built in other locations.
Transfer Android 11 camera videos to Ubuntu 20.10 by Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01ARM-based servers.
Paging makes it easier to compile and run two programs or threads at the same time on a single computer.
For example, when you compile two programs, the compiler does not know if they are going to be running at the same time or not.
And thread stacks, that must be contiguous and keep growing down until they overwrite each other, are an even bigger issue!
But if two programs use the same address and run at the same time, this is obviously going to break them!
Paging solves this problem beautifully by adding one degree of indirection:
(logical) ------------> (physical)
pagingWhere:
As far as programs are concerned, they think they can use any address between 0 and 4 GiB (2^32,
FFFFFFFF) on 32-bit systems.The OS then sets up paging so that identical logical addresses will go into different physical addresses and not overwrite each other.
This makes it much simpler to compile programs and run them at the same time.
Paging achieves that goal, and in addition:
- the switch between programs is very fast, because it is implemented by hardware
- the memory of both programs can grow and shrink as needed without too much fragmentation
- one program can never access the memory of another program, even if it wanted to.This is good both for security, and to prevent bugs in one program from crashing other programs.
Or if you like non-funny jokes:
Comparison between the Linux kernel userland memory virtualization and The Matrix
. Source. Is this RAM real?
x86 Paging Tutorial 64-bit architectures by Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-07-01 +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.
x86 Paging Tutorial Linux kernel usage by Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01The Linux kernel makes extensive usage of the paging features of x86 to allow fast process switches with small data fragmentation.
There are also however some features that the Linux kernel might not use, either because they are only for backwards compatibility, or because the Linux devs didn't feel it was worth it yet.
It is mindblowing that the sale wasn't cancelled due to anti trust.
The outcome of this is that WhatApp will remain with the same feature set forever, while other competitors have been growing, notably Discord and Slack.
It seems that there is a case looming 10 years after the fact: www.cityam.com/facebook-fails-to-block-antitrust-lawsuit-over-whatsapp-and-instagram-ownership/ Wake up???
History of the University of Oxford by Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01This book series appears to be the one: global.oup.com/academic/content/series/h/history-of-the-university-of-oxford-huo/. A mere 250 pounds+ each.
- youtu.be/uol4V1Wa8B0?t=343 at the University of Bologna, the original system was for students to decide what they would learn, and hire and fire teachers as they decided. This is opposed to the system of the university of Paris, in which teachers make the final decisions. He mentions that this is the system that the University of Oxford and the University of Cambridge use: the "congregation". He mentions that Oxbridge are one of the few universities that maintained this structure (as opposed to having funding sources select the final decision makers)
- youtu.be/uol4V1Wa8B0?t=1327 mentions the quadrangle architecture which served as the basis of the Colleges: make a closed square with everything students need: Chapel, Hall to eat, classes and accommodation. This is based of course on monastic cloisters.
Entrepreneurship at the University of Cambridge by Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
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