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What exactly is "iowait"?
To summarize it in one sentence, 'iowait' is the percentage
of time the CPU is idle AND there is at least one I/O
in progress.
Each CPU can be in one of four states: user, sys, idle, iowait.
Performance tools such as vmstat, iostat, sar, etc. print
out these four states as a percentage. The sar tool can
print out the states on a per CPU basis (-P flag) but most
@jemmanuel
jemmanuel / reallocation.md
Created April 10, 2020 14:26
Optimal memory reallocation and the golden ratio

This is based on a neat little post that I saw on Simon Frankau‘s blog that I thought I’d provide a few more details on, as well as bringing it to a wider audience. Some higher-level data structures in object-oriented programming languages have dynamic memory allocation. This is used to create objects (usually things that behave like lists) that can grow and shrink as the program executes. When initializing a regular array in C or Java, you have to specify the size of the array on creation, for example with

int myArray[] = new int[10];

macOS Internals

Understand your Mac and iPhone more deeply by tracing the evolution of Mac OS X from prelease to Swift. John Siracusa delivers the details.

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