Memory layout

Join For Free Sensu is an open source monitoring event pipeline. When working with multi-dimensional arrays, one important decision programmers have to make fairly early on in the project is what memory layout to use for storing the data, and how to access such data in the most efficient manner. Since computer memory is inherently linear - a one-dimensional structure, mapping multi-dimensional data on it can be done in several ways.

Memory layout

Memory layout

About the content This talk was delivered live in October at goto; Copenhagen. The video was transcribed by Realm and is published here with the permission of the conference organizers. Download Slides Introduction 0: I have a blog where I do all sorts of crazy stuff. I enjoy taking things apart to see how they tick and I have a bunch of crazy Memory layout projects which you should probably never use for anything, but are lots of fun to play with.

I also have a cat and as you know the internet is all about cats, and we are fundamentally all about the internet these days.

I also have a lot of fun flying gliders. You have to keep track of where you are. Figuring out how to build hardware which can remember things and store information to dig out later is one of the fundamental problems in computing. There have been lots of technological developments to improve how we solve this problem.

The first solution was vacuum tubes. They were very large, essentially incandescent light bulbs that each hold one bit. So if you wanted to store some reasonable amount of data you would have to have a room full of incredibly hot equipment.

Later on there were mercury delay lines, which was a large pipe filled with mercury that had something like a speaker at one end and a microphone at the other, used to pulse your data through the mercury.

Since it takes time for the information to travel down the tube, it can be used to store data. Magnetic core memory was small rings of iron with wires running through them, and depending on the electrical current you sent through them, you could store or retrieve data using the magnetic field in those rings, with one ring per bit.

For comparison, a smartphone can hold many billions of bits. These small chips allow us to store billions and billions of bits of information all at once. In the Eyes of a Programmer 4: So how does memory look for a programmer?

The fundamental unit of information is the bit, which is 1 or 0. Traditionally we organize bits in groups of eight, called bytes.

Memory is just a long sequence of bytes, one after the other, heading off into the mist. But they are arranged in a certain order. Every byte gets a number called its address. Often we view memory organized by word instead of by byte. On modern devices 64 bits is expressed as 8 bytes. Memory is usually mapped in hexadecimal.

Hexadecimal is where you use base 16 addressing instead of base 8.

Memory layout

The numbers increase from 0 to 9 and then A through F, before working back around to [[email protected]]$ gcc memory-layout.c -o memory-layout [[email protected]]$ size memory-layout text data bss dec hex filename 8 4c0 memory-layout 2.

Let us add one global variable in program, now check the size of bss (highlighted in red color). Anatomy of a Program in Memory. Jan 27th, Finally, the virtual address layout described above is the "flexible" layout in Linux, which has been the default for a few years. It assumes that we have a value for RLIMIT_STACK.

When that's not the case, Linux reverts back to the "classic" layout . The processor offloads the memory layout transform to the HAMLeT, and the data reorganization is handled in the memory by avoiding the latency and energy overhead of.

Similarly, in column-major layout of multi-dimensional arrays, the first index is the fastest changing. Given a -dimensional array, we compute the memory location of an element from its indices as. A typical memory representation of C program consists of following sections: Text segment, Initialized data segment, Uninitialized data segment, Stack, Heap.

DDR Memory Layout Design: Rules, Factors, Considerations Tweet Jump rope is a popular childhood activity involving two people swinging the ends of a long rope, with a third person in the middle skipping each time the rope swings under their feet.

File:Linux Virtual Memory Layout - Wikimedia Commons