Theoretically: 16.8 million terabytes. In practice: your computer case is a little too small to fit all that RAM.
http://en.wikipedia.org/wiki/64-bit#Limitations_of_practical_processors
Я читаю книгу о своей компьютерной архитектуре и вижу, что в 32-битном процессоре x86 счетчик программ 32-битный.
Таким образом, число байтов, которые он может адресовать, составляет 2 ^ 32 байта или 4 ГБ. Поэтому для меня имеет смысл, что большинство 32-битных машин ограничивают объем оперативной памяти до 4 Гб (игнорируя PAE).
Прав ли я, предполагая, что 64-битная машина теоретически может адресовать 2 ^ 64 байта или 16 эксабайт оперативной памяти ?!
Theoretically: 16.8 million terabytes. In practice: your computer case is a little too small to fit all that RAM.
http://en.wikipedia.org/wiki/64-bit#Limitations_of_practical_processors
To supplement Matt Ball's answer, the current largest stick of RAM I can find on one particular online retailer is 32GB. It would take 32 of these to reach 1 terabyte. At about a half inch per stick this brings us to a devoted 16 inches of space on your motherboard for a terabyte of commercial ram. To reach 16.8 million terabytes would require a motherboard 4,242.42 miles. The distance from LA to NYC is about 2141 miles, so the motherboard would stretch across the country and back to accomodate that much RAM.
Clearly this is impractical.
How about we didn't put our RAM all in one row like on most motherboards, but instead placed them side-by-side. I want to say the average stick of ram is about six inches long, so if we allow a half an inch for width, you can have a square unit of 12 sticks of ram in a 6 inch square. Let's call this square a RAM-tile. A RAM-tile then holds 384GB of RAM. To reach the required 16.8 million terabytes in 384GB tiles would take 44.8 million tiles. Let's be messy, and use square root of that to conclude that this will fit in a square of 6693 by 6694 tiles, or 13,386 by 13,388 feet, which is close enough to 2.5 miles squared, enough to cover downtown Seattle in shadow, as if they didn't already have enough to complain about.
Effectively, yes - processes could, in theory, address 2^64 bytes of memory. But as you pointed out, there are ways around this limit.
There is no particular fixed relationship between the bit size of a processor and the amount of addressable memory. Most 8-bit machines of the late 1970s could easily access 65,536 bytes directly, the 16-bit 8088 and 8086 could access 1,048,576 bytes directly. Additionally, it's possible to add hardware to allow machines to access any quantity of RAM indirectly; many machines with 8-bit processors had 128K or more, and memory-expansion units for 8088-based PCs could access over 16 megs. Although Microsoft only enabled such feature in "server" versions of Windows, it was possible for 32-bit code to access memory beyond the 4GiB mark using similar approaches.
You would be correct. You can address up to 16 exabytes of RAM. Now.. whether the operating system can handle it would be another question....
Would be also good to note that the operating system has its own limitation about memory in a 64-bit architecture.
For example, see what wikipedia sais about Windows Vista 64:
All 64-bit versions of Microsoft operating systems currently impose a 16 TB limit on address space. Processes created on the 64-bit editions of Windows Vista can have 8 TB in virtual memory for user processes and 8 TB for kernel processes to create a virtual memory of 16 TB.[29] In terms of physical memory Windows Vista 64-Bit Basic supports up to 8 GB of RAM, Windows Vista 64-Bit Home Premium supports up to 16 GB of RAM, and Windows Vista 64-Bit Business/Enterprise/Ultimate supports up to 128 GB of RAM.[8]
The biggest advantage to 64 bits is not the RAM it can address, but everything else. You can define an address for every byte on a disk, for example, and increasing disk capacities will not invalidate this for decades.
Most of today's current processors have some sort of artificial limit on their address size. For example, the AMD64 architecture has a 52-bit limit on physical memory and currently only supports a 48-bit virtual address space. (Via Wikipedia). However yes, physically ~16.4 million terabytes is possible.
for a realistic physical answer 1536gb with 48 ram cards runing 32gb single sticks and 4x lga2011 xeons
this is for the esayist pc someone can buy without breaching hidden hardcore severs think theres 64gb single stics brings to.... 3072gb 128gb be 6144gb 256gb be 12288gb
just to throw out there that theres ways to get around os limitations with ram if ur os can only see 4gb ram turn the leftover into a ram drive and use the ram drive as page file XD XD XD XD just a matter of making a preboot os system some such simular thing was done back in early days of dos/windows 3.11 etc
and there can be other little hacks for getting around cpu limitations
gear we can see isnt wats out there theres way more potent stuff i had a pc from 98 runing 8 proccessors and somethink like 32gb ram but this is expensive hi end servers
im looking into servers as desktops because im sick of the computers for the public XD