Каковы более низкие преимущества уровня и недостатки 64-bit/32-bit?

The difference is exactly 32 bit ;-)

You need 64 bit hardware (processor) to run a 64 bit OS. You need a 64 bit OS to run 64 bit software. This are the dependencies.

• In a 32 bit system you are limited to addressing 4 GiByte (2^32) memory, in a 64 bit there is a theoretical limit of 2^64 byte.
• 64 Bit software needs slightly more memory, mainly for pointers are 8 Bytes instead of 4
• on x86_64, 64 Bit executables need more memory, as there is an additional opcode for many instructions, and thus may run slower
• on x86_64, 64 Bit software can use more registers and has the potential to run faster

• 64bit systems can directly address significantly more memory
• 64bit systems can process data in chunks twice as large as 32bit, which helps some operations go more quickly

For some programs, like office automation suites, 32bit vs 64bit makes little observable difference.

But for other applications, such as databases, graphics/video processing, or hosting virtual machines, being able to reach more physical memory at once and being able to process more information with each instruction can make a huge difference in performance.

Note that today, many 32bit chips have 64bit extension functions, as many FPU (math) or SSMD (vector) operations are done in 64bit mode already.

See 32-bit Vs. 64-bit Systems: What's The Difference? for more.

I think the best answer would be a comparison in x86 bit x64 assembler

When your x32 bit program registers a variable,for example an integer(5),the code is equivalent to this:

push 5

To Understand things better,'push X' is a shortcut to:

sub esp,4 //substracts esp with 4(4*8=32 bits.That's the size of a pointer in x32 executables) in order to make space for our variable
mov [esp],X //moves variable in @esp

Those registeres are 32 bit(4 bytes long),which is the size of a pointer in any 32 bit programming language.

In 64 bit code,however the size is twice bigger and so are registers.Our register ESP exists in x64 executables,but its not widely used as it is in x32 executables.

Instead all of the registeres get a "R" in front of their name(EAX becomes RAX,ESP becomes RSP,EDX becomes RDX and so on).

So our code in x64 executable won't be any different,except the shortcut for 'push X' will be

sub esp,8
mov [rsp],X

RSP has double the size of ESP - 64 bits,8 bytes.

The bottom line is that x64 bit executables use more memory than x32 bit executables.

1. CPU registers and memory addressing.

2. The system can reference (see) much more memory.

Let's go back to the basics.

99% of computer these days are based on what is referred to as the Von Neumann architecture. Essentially, the computer is in a constant cycle of:

1. Fetching a command from RAM
2. Executing the command on the CPU

_{(source: wikimedia.org)}

When referring to 32/64-bit system (or any other bit size), essentially you are talking about the architecture and implementation of the computer:

• size of memory space (RAM)
• size of CPU registers
• bus size (i.e. between CPU, RAM, I/O, etc...)

If you have a 64-bit system, you have an address space of 2^64. This is why 32-bit system cannot have more than 4GB of RAM. How can you address a memory space which is larger than 2^32?

Regarding the performance differences, there is no clear cut answer (just as there is no clear answer if CISC or RISC architecture is better). It vastly depends on the applications you are using.

To sum: a 64-bit architecture is simply a different way to build a computer. It does not mean it is better, or worse, or does things differently (on a low level, every computer is doing fetch-execute). It's simply a different way of implementing a computer.

Exactly the 64bit or 32bit references just to the width of the main bus.