above chain of mail raises more confusion as conflict stays till end.
1)processor 32/64 bit --
a)data it can process at one instance --- register size --- data bus size --
OR
b)internal address bus size of processor --- if that is true then what abt case of pentium 36 bit address lines ---
2)OS 32 /64 bit
a)its virtual address space -- what os provides --- to each process -- which is mapped to physical address space that prcessor provides
OR
b)processor specifies virtual addr space ??
3)extra ques -- why in case of 32 bit arch -- physical memory RAM limitation comes of 4GB ?
On Fri, Oct 23, 2009 at 4:54 PM, <microbit@xxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi,
No it doesn't... the previous poster is right. (unless we excessively get
On Thu, 22 Oct 2009 23:58:20 -0700, C <a.la.kaarta@xxxxxxxxx> wrote:
>> Well, IMHO the processor does not decide or even know the size of
>> virtual address space.
> Ofcourse it does. How else do you think it translates a virtual
> address to a physical address? Virtual addresses are simply what the
> software 'sees', the processor takes these, translates them into
> physical addresses before making any reads / writes to main memory. No
> software can use a virtual address space larger than what the
> processor specifies.
>
>> 1) User may run a firmware on the processor that gives a 1-1 mapping
>> from virtual to physical (thus making virtual address space equal to
>> physical address space).
>>
> Well, I don't know much about other architectures, so I'll just comment
on
> x86.
> When you switch to 64bit mode, you compulsorily need to have a 4-level
> paging table, which translates 64-bit linear addresses (actually a
> 48-bit linear address, since the address is subject to the canonical
> address requirement) to (upto) 52-bit physical addresses. So
> irrespective of what firmware you're running, linear addresses are
> actually 64-bit, but physical addresses are not.
>
> (In fact, physical address space might even be larger than virtual
> address space, when we take modes like PAE / PSE into account)
>
>> 2) Users may be running different OS(s) that give different amount of
>> virtual address space to use.
> Irrespective of what OS you're using (and whether it switches to the
> processor mode that would utilize the 64-bit virtual address space
> that the processor provides), the 'internal address bus' (virtual
> address space) of the processor is what decides the maximum virtual
> address space of any programs that run on it (OS or otherwise).
>
> C
>
> On Thu, Oct 22, 2009 at 11:23 PM, Rajat Jain <Rajat.Jain@xxxxxxxxxxxx>
> wrote:
>>
>> Hi,
>>
>> ----Original Message----
>> From: C [mailto:a.la.kaarta@xxxxxxxxx]
>> Sent: Friday, October 23, 2009 10:51 AM
>> To: Rajat Jain
>> Cc: simonyanix@xxxxxxxxx; Siddu; Rick Brown; kernelnewbies;
>> linux-newbie@xxxxxxxxxxxxxxx
>> Subject: Re: 32 bit processors / 64 bit processors
>>
>>> PAE (Physical Address Extension) expands the _physical_ address space
>>> to > 32 bits, but the _virtual_ address space stays the same at
>>> 32-bits, and the virtual address size is what I mentioned as qualifies
>>> the processor as 32-bit or 64-bit.
>>
>> Well, IMHO the processor does not decide or even know the size of
>> virtual address space.
> Ofcourse it does. How else do you think it translates a virtual
> address to a physical address?
>
> It purely depends on the software (OS in this
>> case) that runs on it. Consider all of the following is possible on the
>> same 32 bit processor:
>>
>> 1) User may run a firmware on the processor that gives a 1-1 mapping
>> from virtual to physical (thus making virtual address space equal to
>> physical address space).
>>
>> 2) Users may be running different OS(s) that give different amount of
>> virtual address space to use.
>>
>> What am I missing?
>>
>> Thanks,
>>
>> Rajat
>>
>>
>>>
>>> 1. Addressable physical memory / physical address size does not decide
>>> whether a processor is 32-bit / 64-bit, there is no processor (AFAIK)
>>> which can address 64 bits of physical memory. I suppose sizeof(void*)
>>> gives you the size of the _virtual_ address, so yes, I suppose that
>>> should be 64 bits on a 64-bit processor (and using a 64-bit compiler)
>>> 2. Register size does not decide whether a processor is 32-bit /
>>> 64-bit.
>>>
>>> C
>>>
>>> On Thu, Oct 22, 2009 at 10:05 PM, Rajat Jain
>>> <Rajat.Jain@xxxxxxxxxxxx> wrote:
>>>>
>>>> Hi,
>>>>
>>>>> 1. The size of the processor's internal address bus (virtual address
>>>>> space) is what qualifies it as a 32-bit / 64-bit processor.
>>>>
>>>> Well, in that sense, isn't Pentium a "36-bit" processor (since it
>>>> gives the option of PAE to use 64 GB of memory - it must be having
>>>> atleast 36 address lines)?
>>>>
>>>> On this topic and in this thread, we have had following responses to
>>>> the question on what is called a 32-bit or 64-bit processor:
>>>>
>>>> 1) Addressable Physical memory (=sizeof(void*))
>>>> 2) Register Size (=instruction size)
>>>>
>>>> Are the above two independent of each other? If yes, then how do we
>>>> deine a processor as 32-bit / 64-bit?
>>>>
>>>> Thanks,
>>>>
>>>> Rajat
>>
>
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>> Well, IMHO the processor does not decide or even know the size of
>> virtual address space.
> Ofcourse it does. How else do you think it translates a virtual
into semantics....)
That is up to the MMU, it has absolutely nothing to do with the CPU.
And FWIW, x86 is hardly a reference... x86, along with 8051 would have to
be the biggest abonimation
to the concept of elegant processing......
-- Kris
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Thanks & Regards
Nidhi Mittal Hada
