Talk:Virtual address space

message: This article has references that are specific to IA32. For example, it talks about 4GB address space. It could be different on other architectures. Raanoo 13:30, 24 July 2007 (UTC)
thread_title: Assumptions that need a fix

message: Is the virtual address space defined by the hardware (as in "all addresses for which the OS could provide a mapping") or by the hardware and the OS (as in "all addresses for which the OS actually would provide such a mapping if a reference is made to the address")?  In the former case, the address space, for most if not all non-segmented systems, would include address 0, and would consist of a small number of regions (typically 1 or 2, e.g. 2 in x86-64 with current implementations); in the latter case, for most OSes, it would not include 0, and might include several regions.
Or, to put it another way, in the diagram on the page, are the gray areas part of the virtual address space (in which case it's defined by the hardware) or not (in which case it's defined by the software)? Guy Harris (talk) 18:03, 26 August 2013 (UTC)
replies: text: It seems to me that it's a combination. The architecture defines the maximum possible size and the software decides what to actually make available. "Would" or "does" is more appropriate. Peter Flass (talk) 15:39, 27 August 2013 (UTC)
replies: text: Yes, "by the hardware and the OS" is "a combination", so you're saying it's "by the hardware and the OS". Guy Harris (talk) 16:29, 27 August 2013 (UTC)
replies: text: You could have an address space smaller than the maximum amount of memory the CPU can address, or as you mention an address space can have holes.  The hardware defines the maximum and the OS can further restrict it.  Another question - is the concept of "address space" relevant to segmented systems such as Multics?  Still another - are there any systems besides SVS that use a single shared address space for all processes? Peter Flass (talk) 19:07, 27 August 2013 (UTC)
replies: text: "are there any systems besides SVS that use a single shared address space for all processes?"  Yes. Guy Harris (talk) 19:52, 27 August 2013 (UTC)
thread_title:  What is, and what isn't, part of the virtual address space? 

message: Even in the windows-specific example, I don't believe the references to the page file are required to make the point. Peter Flass (talk) 07:31, 28 August 2013 (UTC)
replies: text: You are correct. You don't need a pagefile to use v.a.s. that isn't mapped to exes or dlls or etc. And the notion that (in Windows terms) VirtualAlloc'd v.a.s. is "mapped to the pagefile" is incorrect. (There is such a thing as a "pagefile-backed section", but still, it isn't really "mapped to the pagefile".) First, again, you don't need a pagefile at all to create private committed address space (or even pagefile-backed sections!). Such v.a.s. is backed by the pagefile if you have one, but to say that it is mapped to the pagefile implies that there is a specific relationship between pages of v.a.s. and page locations in the pagefile that's set up when the region is created, but that's not the case. Such relationships are only established if and when things have to be written to the pagefile. In addition, you get a page fault the first time you touch both process-private and mapped virtual pages, just like you will if you touch a page that isn't defined yet. It's just that in the latter case the PF can't be resolved, whereas in the other two, it can be. That entire discussion needs to be rewritten. Jeh (talk) 18:00, 15 July 2016 (UTC)
thread_title:  Example 

message: Despite the edit comment that accompanied this change, the /3GB switch and "4 GB chipsets" are not directly related to each other. The former controls the division in virtual address space between user mode and kernel mode, per-process and system-wide. The latter has to do with how much physical  memory the machine can address. All four possible combinations of "/3GB switch on or off" and "4 GB chipset or not" are possible and efficacious; the location of the U/K boundary in virtual address space is not directly related to how much RAM you have. Jeh (talk) 17:26, 15 July 2016 (UTC)
thread_title:  Re the /3GB swtich and 4 GB chipsets 

message: In response to this edit: note that Wikipedia does not commonly use the binary prefixes (Gi, Mi, etc) for computer units, see WP:COMPUNITS. -- intgr [talk] 09:52, 21 August 2017 (UTC)
thread_title:  Computer unit prefixes