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 PostPost subject: How virtual memory works in Mac OS        Posted: Sat Jun 06, 2015 10:38 am 
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Hello all,
few days later someone asked me about how virtual memory works on Windows, Mac, and other OS. And that moment was so embarrassing for me that I didn't know much about that but then I had searched the topic on Google but still cant understand much to tell somebody else. Can anybody suggest me, any help would be appreciated….

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Last edited by lilysmith22 on Mon Jun 08, 2015 12:38 pm, edited 1 time in total.

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 PostPost subject: Re: How virtual memory works in Mac OS        Posted: Sat Jun 06, 2015 5:19 pm 
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OS X? It's Mach+BSD .. Classical Mac OS? I'm not sure youd have to go through that leaked souce for 7

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 PostPost subject: Re: How virtual memory works in Mac OS        Posted: Mon Jun 08, 2015 12:39 pm 
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louisw3 wrote:
OS X? It's Mach+BSD .. Classical Mac OS? I'm not sure youd have to go through that leaked souce for 7

Am not getting what you want to know???

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 PostPost subject: Re: How virtual memory works in Mac OS        Posted: Mon Jun 08, 2015 2:57 pm 
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lilysmith22 wrote:
louisw3 wrote:
OS X? It's Mach+BSD .. Classical Mac OS? I'm not sure youd have to go through that leaked souce for 7

Am not getting what you want to know???

He wants to know which version of Mac OS you're talking about. If you're talking about Mac OS X, virtual memory works exactly as in Free/Open/NetBSD + Mach, so you can google that. If you're talking about earlier MacOS versions you'd have to check the leaked source code yourself on how it works, but I guess MacOS didn't have any concept of virtual memory back then

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 PostPost subject: Re: How virtual memory works in Mac OS        Posted: Tue Jun 09, 2015 11:29 am 
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@Darkstar Ohh I got that am using Mac OS X but am knowing exactly how virtual memory works on.... whether it is Mac OS X or Free/Open/NetBSD + Mach....

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 PostPost subject: Re: How virtual memory works in Mac OS        Posted: Mon Mar 20, 2017 9:40 pm 
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Virtual memory goes along with segmentation, paging, and swapping. Basically, through functionality implemented by both the CPU and OS, each process gets it's own 'virtual' address space, composed of one or more pages of memory(fixed-sized portions) that are allocated to it. Then, when that process needs to access something in memory, such as a variable, it provides a virtual address within it's address space to the CPU, which then translates it to a physical or 'real' address using a combination of the page that it is in and the offset within that page.

This as also why you see the 'segmentation fault' error sometimes, the program tried to access memory that it wasn't allowed to access, someone else's page.

This scheme is critical for allowing relocatable code without constantly having to re-address objects in memory when the code is moved, such as when pages are swapped in/out during swapping. Works more or less the same on all modern operating systems and machine architectures.

Virtual memory allows cool stuff like having ten programs read/write address zero, and none of them actually reading/writing address zero!


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