I am creating a quite simple application which reads and display text files and search through them.
I am asking myself if there is any interest for me to propose 32 and 64 bits version to the user.
Is the difference only in having access to more memory heap size with the 64 bit version or is there any other interest ?
Will a 32 bit compiled program work on a 64 bits JVM (I assume yes)
The only differences between 32-bit and 64-bit builds of any program are the sizes of machine words, the amount of addressable memory, and the Operating System ABI in use. With Java, the language specification means that the differences in machine word size and OS ABI should not matter at all unless you're using native code as well. (Native code must be built to be the same as the word-size of the JVM that will load it; you can't mix 32-bit and 64-bit builds in the same process without very exotic coding indeed, and you shouldn't be doing that with Java about.)
The only times that have swung it for me is when there have been native libraries involved that have pushed it one way or the other. If you're just in Java land then realistically, unless you need >4GB of heap size, there's very little difference.
EDIT: The differences include things like it uses slightly more memory than 32 bit, significantly more if you're using a version before 6u23 and aren't using -XX:+UseCompressedOops. There may also be a slight performance difference between the two, but again nothing huge.
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Actually I want to link 64 bit library to my 32 bit application.
I want to use a library which works faster under 64 bits under some circumstances. But i have to link that library to my 32 bit application . Is it possible or not ??
In a word, no. The only way to get compiled 64bit code talking to compiled 32bit code is via some form of IPC (e.g. pipe, named pipe, or network connection). That may well introduce performance bottlenecks of its own, so probably isn't worth the bother.
It is not easy as #robthebloke mentioned. But NVIDIA RTX Remix Runtime does it somehow, making older 32bit games running on 64-bit vulkan driver (bypassing 2-4GB virtual memory limit).
Have anyone tried to compile glibc with -march=corei7 to see if there's any performance improvement over the version that comes by default with any Linux x68_64 distribution? GCC is compiled with -march=i686. I think (not sure) that the mathematical library is also compiled the same way. Can anybody confirm this?
Most Linux distributions for x86 compile using only i686 instructions, but asking for scheduling them for later processors. I haven't really followed later developments.
A long while back different versions of system libraries according to processor lines were common, but the performance differences were soon deemed too small for the cost. And machines got more uniform in performance meanwhile.
One thing that has to be remembered always is that today's machines are memory bound. I.e., today a memory access takes a few hundred times longer than an instruction, and the gap is growing. Not to mention that this machine (an oldish laptop, was top-of-the-line some 2 years back) has 4 cores (8 threads), all battling to get data/instructions from memory. Making the code run a tiny bit faster, so the CPU can wait longer for RAM, isn't very productive.
I'm a beginner programmer in my first year of Computer Science.
I'm curious about the 32 bit and 64 bit systems, and how it affects developing software.
When I download software I need to choose between the two, while other software only has a 32 bit version.
Are there different ways of programming for a 64 bit system?
Is it compiled in the same way?
What are the main benefits of a separate 64 bit app?
Cheers
Are there different ways of programming for a 64 bit system?
Yes and no. No, in the sense that most of the time you should be able to write platform-independent code, even if you are coding in a language like C. Yes, in the sense that having knowledge of the underlying architecture (not just the word size!) helps to speed up critical parts of your program. For instance, you may be able to use special instructions available.
Is it compiled in the same way?
Again, yes and no. Compilers for systems languages work in similar ways for all architectures, but of course, the details differ a bit. For instance, the compiler will use knowledge about your architecture to generate as efficient code as possible for it, but also has to take care of differences between architectures and other details, like calling conventions.
What are the main benefits of a separate 64 bit app?
I assume you are asking about the usual desktop CPUs, i.e. x86 architecture, but note that there are other architectures with word sizes ranging from 8-bit to 128-bit. Typically, people would compile a program targeting a single architecture (i.e. for a given machine), and that's about it.
However, x86 is a bit special, in that the CPU can operate in different modes, each with a different word size: 16-bit, 32-bit and 64-bit (among other differences). Effectively, they implement several ISAs (Instruction Set Architectures) in a single CPU.
This was done to preserve backwards compatibility, and it is key to their commercial success. Consider that, when people bought the first 64-bit capable CPUs, it was most likely that they were still using 32-bit operating systems and software, so they really needed the compatibility. The other options are emulating it (poor performance) or making sure all the popular customer software has been ported (hard to achieve in ecosystems like Windows with many independent, proprietary vendors).
There are several benefits of 64-bit x86 over 32-bit x86: more addressable memory, more integer registers, twice the XMM registers, a better calling convention, guaranteed SSE2... The only downside is using 64-bit pointers, which implies more memory and cache usage. In practice, many programs can expect to be slightly faster in x64 (e.g. 10%), but pointer-heavy programs may even see a decrease in performance.
Generally speaking the main benefit of 64 bit application is that it has access to more memory. Having 32 bit pointer you can access only 4GB of memory.
Most modern compilers have option to compile either 32 bit or 64 bit code.
32/64 coding is the same unless you are dealing with huge in-memory objects, where you would need to use 64 bit specifically.
An interesting fact/example is that Unix time is stored as a single number. It is calculated as a number of seconds passed from January 1st 1970. This number will soon reach 32-bit size, so eventually we will have to upgrade all of our systems to 64-bit so they can hold such a large number.
I am running 32bit ubuntu on 64bit x86 processor (intel). I know that the word size is 64bits in this case but I am little confused about the 32bit OS.
So while I calculate the memory bandwidth, shall I assume that the data bus width of 64 lines will be used and it will exhibit the same performance as the 64bit OS? IOW, I want to better understand the relation between OS width on the architecture width.
For instance, a 64bit operand can be read in single shot with a 64bit wide memory bus. Does this need the support of 64bit OS? With a 32bit OS, will it make two reads (32bits each time) to read the 64bit operand?
Thanks!
You shouldn't worry about this.
OS 32-bit vs. 64 bit is deffer only on memory addressing. IN 64-bit you may addres more.
Data loading from memory is independent from OS - it depends on processor architecture.
Better processor may load 128, 256 bits at one memory load.
It is shortest explanation and should be true in 99,9% of programs running on this OS.
0,1% if reserved for programs, that doesn't care about memory aligment when accessing data. But this problem may be addressed in next 99,9% by processor cache.
Summarizing - you shouldn't worry if your OS has enough memory to run all programs.
Applications compiled for a 32 bit OS don't even know that the bus is 64bits large, they will always use the first 32bits only.
Because the processor is NOT running in 64bits mode, your 64bits data will be stored in two distinct registers (say EAX:EDX), reading two distinct parts of the same number, using the first 32bits of the bus.
Can I use the assembly routines for Serpent encryption in the link below written for 32-bit x86 from a 64-bit program on an x86-64 machine? That is, without launching a separate 32-bit process for it? If not, does anyone have a pointer to an optimized implementation of Serpent that works in both 32 and 64 bit (LGPL is OK but cannot use GPL since it's a commercial project)?
http://gladman.plushost.co.uk/oldsite/cryptography_technology/serpent/serpent.asm
You will need to convert the portions of the code that transfer the results and data to/from memory to use 64-bit address registers. Also, stack manipulation code will need to use the 64-bit stack registers. Other than that, it's likely to work without major changes.
This code seems compatible, at least for me (generally, IA32 assembly is pretty backward-compatible, as sizes of registers do not change, there are just new ones added on x86-64). Also, best way is to check it by yourself.