Address space pressure was immense back in the day, and plain doubling the width of everything while retaining the compatablity was the obvious choice.
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Address space pressure was immense back in the day, and plain doubling the width of everything while retaining the compat[i]blity was the obvious choice.
PAE (https://en.wikipedia.org/wiki/Physical_Address_Extension) existed for quite some time to enable x86-32 processors to access > 4 GiB of RAM. Thus, I would argue that if the OS provided some functionality to move allocated pages in and out of the 32 bit address space of a process to enable the process to use more than 4 GiB of memory is a much more obvious choice.
> Thus, I would argue that if the OS provided some functionality to move allocated pages in and out of the 32 bit address space of a process to enable the process to use more than 4 GiB of memory ...
Oh, no. Back then the segmented memory model was still remembered and no one wanted a return to that. PAE wasn't seen as anything but a bandaid.
Everyone wanted big flat address space. And we got it. Because it was the obvious choice, and the silicon could support it, Intel or no.
PAE got some use - for that “each process gets 4GB” model you mentioned in Darwin and Linux - but it was slower and didn’t allow individual processes to easily use more than 2-3GB in practice.
Address space pressure was immense back in the day, and plain doubling the width of everything while retaining the compatablity was the obvious choice.