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If All You Have Is a Database, Everything Looks Like a Nail
Databases are fabulous resources. Of course, we’ll abuse them in ways that cause challenges.
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Time Machine in macOS 10.15.3 is very slow on first full backup
When making a first full backup of less than 2 GB takes 86 minutes, and you then can’t restore from it anyway.
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Point of WebGPU on Native
WebGPU is a new graphics and compute API designed on the grounds of W3C organization (mostly) by the browser vendors. It’s designed for the Web, used by Java...
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What would happen if computers never got any faster?
My first computer was a BBC Micro. It could do basic graphics at a resolution of 640×256 - with 8 different colours. Not a typo. Eight! The mono speaker produced bleeps and bloops. It was basic, in all senses of the word. Eventually, talented hackers found a way for it to do simplistic 3D graphics and even speech…
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Clocking a 6502 simulator to 15GHz
6-5-0-who? The 6502 is an iconic processor that dominated home computing in the late 70s and early to mid 80s. It was used in machines ra...
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Scaling Linux Services: Before accepting connections
Theo Julienne is a software & infrastructure engineer.
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Which Machines Do Computer Architects Admire? (2013)
The Toolsmith Conference was held in Chapel Hill, NC, in October, 2001, to honor Fred Brooks. Dr. Brooks was a student of Howard Aiken at Harvard, joined IBM to work on the Stretch Project, and later served as chief architect of the IBM S/360. He founded the Computer Science Department at UNC-Chapel Hill in 1964 and…
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It used to be simpler to teach Unix
When I began teaching Unix around anno 1986, the Unix ls(1) utility printed a list of files to stdout, one per line. It was trivial to explain the concept of not requiring a program which tells you...
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Is macOS Becoming Unmaintainable?
Provision of maintenance procedures and tools is at the heart of software engineering, but not in macOS.
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An introduction to virtual memory
...and the crucial role it plays in modern operating systems.
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Computers Can Be Understood
Computers and computer systems are build up from deterministic, comprehensible, building blocks. Their operations and behaviors can be understood and reasoned about. I relate my personal beliefs and mindset on this point, and explore some manifestations and ramifications of this philosophy.
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Writing a Memory Allocator (2019)
Video lectureMutator, Allocator, CollectorMemory blockAllocator interfaceMemory alignmentMemory mappingFreeing the objectsBlocks reuseFirst-fit searchAssignmentsNext-fit searchBest-fit searchBlocks splittingBlocks coalescingExplicit Free-listSegregated-list searchOptimizing the storageCustom sbrkConclusion This is the…
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Faster Integer Parsing
Back with a post after 6 years of silence. If you had to parse a microsecond-resolution epoch timestamp as quickly as possible, how would you do it? We’ll take a look at using compiler intrinsics to do it in log(n) time.
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APFS changes in Big Sur: how Time Machine backs up to APFS
APFS adds 6 volume roles, including one which supports Time Machine backups. And per-file encryption is coming.
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Using TLA+ in the Real World to Understand a Glibc Bug
TLA+ is a formal specification language that you can use to verify programs. It’s different from other formal verification systems in that it’s very pragmatic. Instead of writing proofs…
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Fakecracker: NetBSD as a Function Based MicroVM
In November 2018 AWS published an Open Source tool called Firecracker , mostly a virtual machine monitor relying on KVM , a small sized Linux kernel, and a stripped down version of Qemu . What baffled me was the speed at which the virtual machine would fire up and run the service. The whole process is to be compared…
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Writing Software to Last 50 Years
Design principles for writing software meant to survive decades of changing requirements and technology.
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MMU gang wars: the TLB drive-by shootdown
T The problem Every once in a while I get involuntarily dragged into heat...
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Was Acorn's RISC OS an under-appreciated pearl of OS design?
I was a huge Archimedes fan and still have an A310, an A5000, a RiscPC and a RasPi running RISC OS. But no, I have to disagree. RISC OS was a hastily-done rescue effort after Acorn PARC failed to make ARX work well enough. I helped to arrange this talk by the project lead a few years ago. RISC OS…
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A log/event processing pipeline you can't have (2019)
Let me tell you about the still-not-defunct real-time log processing pipeline we built at my now-defunct last job. It handled logs from a la...
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An History of Nvidia Stream Multiprocessor
I spent last week-end getting accustomed to CUDA and SIMT programming. It was a prolific time ending up with a Business Card Raytracer running close to 700x faster [1] , from 101s to 150ms. This pleasant experience was a good pretext to spend more time on the topic and learn about the evolution of Nvidia architecture…
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I'm back into the grind of FreeBSD's wireless stack and 802.11ac
hi! Yes, it's been a while since I posted here and yes, it's been a while since I was actively working on FreeBSD's wireless stack. Life's...
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Is Catalina a Good Upgrade Yet?
Although 10.15.3 fixes a serious bug in Mail and Catalina is steadily maturing, there are many users who still shouldn’t upgrade.
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The Genius of RISC-V Microprocessors
How the instruction set for RISC-V processors has been designed cleverly for both simplicity and high performance.
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How x86_64 Addresses Memory
Update 2025-03-05 : @jxu has shared a collection of simplified examples that are even easier to follow than the original ones in this post.
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Durability: NVMe Disks
Durability is the guarantee that data can be accessed after a failure. It seems like this should be very simple: either your system provides durable data storage, or it does not. However, durability is not a binary yes/no property, and instead should be defined as the kinds of failures you want your data to survive…