CODEWITHSUNDEEP
32bit-64bit
Norsk
Norsk

Reputation: 633

From a programming point of view, what does it mean when a program is 32 or 64 bit?

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.

Cheers

Upvotes: 3

Views: 679

Answers (3)

Acorn
Acorn

Reputation: 26066

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.

Upvotes: 3

Dropout
Dropout

Reputation: 13866

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.

Upvotes: 0

Anton Krouglov
Anton Krouglov

Reputation: 3399

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.

Upvotes: 2

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