From mboxrd@z Thu Jan 1 00:00:00 1970 From: hmthalib Subject: Re: 32 bit processors / 64 bit processors Date: Sat, 07 Nov 2009 16:19:42 +0530 Message-ID: <4AF550C6.8050206@gmail.com> References: <7783925d0910202002ubcd5328nd8c82bb11e5f84ea@mail.gmail.com> <9b0a5b990910202239u7423e88du4786700f79a4bda9@mail.gmail.com> <49FAB6BD-25CD-484D-AC5D-4731D083E075@gmail.com> <4AF54788.6080508@gmail.com> <4AF54C3B.5060606@gmail.com> Reply-To: hmthalib@gmail.com Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:reply-to :user-agent:mime-version:to:cc:subject:references:in-reply-to :content-type:content-transfer-encoding; bh=YgDQE2ibMW2Meyq/BWGCT+IZyPOwVZnm/9PovYxrtZA=; b=Owu5xoGqz5NCcnxI6ujeAFV6vItcvTpFNuApR0QxOV8nssgDtzaFOSYCYOfVlkaxcr YNpbZxYXmxibcH1DICj9RQl/Tqe/wYaLdjvP3FWlv40L52mB2+nh6mI4+TAFHiWRmwxw 8ApWRZZ61KpiElcYmUr7nfywoErg9KBgEEEy4= In-Reply-To: <4AF54C3B.5060606@gmail.com> Sender: linux-newbie-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: viral.vkm@gmail.com Cc: nidhi mittal hada , microbit@virginbroadband.com.au, C , simonyanix@gmail.com, Siddu , Rick Brown , kernelnewbies , linux-newbie@vger.kernel.org vkm wrote: > > > hmthalib wrote: >> nidhi mittal hada wrote: >>> Can someone come and please clarify -- it finally >>> 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 --- >>> >> >> A processor is called 32 bit or 64 bit depending on the width of the >> data bus. not on the register size or data it can process at one instance >> >> for example a 8 bit micro controller can have 16 bit registers. >> similarly all modern processor has architecture to process more data >> to increase the throughput. > > What would you call pentium pro.... Its address bus is 36 bits wide, and > the external data bus is 64 bits wide Oh, you mean I am saying pentium pro as processor, I didn't meant that. so to make clear i will use term SoC today what we get from the semiconductor vendor is SoC may be you have ARM, PowerPC, x86, ia64, AMD , etc... what ever you buy from market is a SoC. your actual processor will site in one corner or your SoC, where there will be other peripherals along the actual processor, because of Multi core core era we call it as core , did you got it now. A processor is just has ALU, Register, control unit, PC , etc.. it is where the actual processing takes palace. there will be data/addr bus connecting all the needed modules which also connects the main memory directly or though cache. when data is move to any registers form memory at a time a 32bit processor will move 32bit to a register. even the register is 64bit or 128bit wide the data will be done in multiple processor cycles. To know more about memory management which done in modern CPU though MMU check the below link http://duartes.org/gustavo/blog/post/anatomy-of-a-program-in-memory >> >> >>> >>> 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 ?? >>> >>> >> >> dont confuse with virtual addr space with physical addr space . MMU >> will assist the OS in this issue. >> >> the moment the bit to enable the 64 bit mode is enabled the MMU and >> other thing are extend to address 64 bit physical addr space. >> >>> >>> >>> 3)extra ques -- why in case of 32 bit arch -- physical memory RAM >>> limitation comes of 4GB ? >>> >>> >> because the 32 bit can only address 2^32 address location which is 4GB >> of RAM max. where 2^64 = 16 EB (exa bytes) >> >> finally download some data sheet of different processor and read to >> get how thing work >> >>> >>> On Fri, Oct 23, 2009 at 4:54 PM, >> > wrote: >>> >>> Hi, >>> >>> On Thu, 22 Oct 2009 23:58:20 -0700, C >> > 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 >>> > >>> > wrote: >>> >> >>> >> Hi, >>> >> >>> >> ----Original Message---- >>> >> From: C [mailto:a.la.kaarta@gmail.com >>> ] >>> >> Sent: Friday, October 23, 2009 10:51 AM >>> >> To: Rajat Jain >>> >> Cc: simonyanix@gmail.com ; Siddu; >>> Rick Brown; kernelnewbies; >>> >> linux-newbie@vger.kernel.org >>> >>> >> 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 >>> >>> > >>> 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 >>> >> >>> > >>> > -- >>> > To unsubscribe from this list: send an email with >>> > "unsubscribe kernelnewbies" to ecartis@nl.linux.org >>> >>> > Please read the FAQ at http://kernelnewbies.org/FAQ >>> >>> >>> >>> >> 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 >>> >>> No it doesn't... the previous poster is right. (unless we >>> excessively get >>> 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 >>> >>> >>> -- >>> To unsubscribe from this list: send an email with >>> "unsubscribe kernelnewbies" to ecartis@nl.linux.org >>> >>> Please read the FAQ at http://kernelnewbies.org/FAQ >>> >>> >>> >>> >>> -- >>> Thanks & Regards >>> Nidhi Mittal Hada >> >> >> -- >> To unsubscribe from this list: send an email with >> "unsubscribe kernelnewbies" to ecartis@nl.linux.org >> Please read the FAQ at http://kernelnewbies.org/FAQ >> >> >> >> Email Scanned for Virus & Dangerous Content by : www.CleanMailGateway.com >> >> > -- Regards, Mohamed Thalib H -- To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs