Difference between 32-bit vs 64-bit JVM in Java?

Hello guys, wish you a very happy new year 2020. I hope you have set all your goals and inspired to achieve them. I have written some articles to help with your goals like The 2020 Java Developer RoadMap and 10 Things Java Programmer Should Learn in 2020. If you haven't made your goals or want to find out some useful resources to achieve your goals you can check out that article. Coming back to this article, it's short but informative one and it's also one of the most asked questions to me on Facebook and LinkedIn, what is the difference between a 32-bit and 64-bit JVM?

While most of the servers now running on 64-bit JVM and its rare to find server-side applications still running on 32-bit JVM, the question may not be relevant in 2020 but it is still something useful to learn and know.

This knowledge will help you to choose the right Java Virtual Machine for your project without compromising performance and memory.

On the same note, a good knowledge of Java virtual machine is essential for any Java developer and you should spend some time this year to learn about JVM internals. If you need a resource, I suggest you join this Java Memory Management course on Udemy, It's a good reference and you can also buy it very low, I bought in just $10.

32-bit JVM vs 64-bit JVM

Without wasting any more of your time, here is some of the key difference between 32-bit and 64-bit Java Virtual Machine

1) 64-bit JVM, you can specify more memory for heap size than 32-bit JVM, like in 32-bit JVM, the theoretical limit for maximum memory in 32-bit is 4G, but 64-bit is much higher.

2) 64-bit JVM is particularly useful for Java application with large heaps, like applications that use more than 100G for max memory.

3) The same Java application will take memory while running in 64-bit JVM then 32-bit because of the increased size of OOP (Ordinary Object pointer), from 32 to 64 bits. Though you can get away with this by using -XXCompressedOOP JVM option, which tells JVM to use 32-bit pointers.

4) Both 32-bit and 64-bit JVM has a separate installer.

5) One more thing that changed in the 64 bit JVM architecture is object header size; it is now of 12 bytes in comparison to 8 bytes headers in 32 bit JVM. Another thing that changed is the size of internal references that means it can go maximum up-to 8 bytes wherein 32 bit JVM up-to 4 bytes.

So, from these two points, you can conclude that an application running on 64 bit JVM will consume more space in comparison when the same application runs on the 32-bit version.

If you need some resources to learn about JVM, there is a three-course series on Pluralsight on JVM which is very good, particularly the Understanding the Java Virtual Machine: Memory Management part, if you are interested and if you have Pluralsight membership, you can check out that course as well.

If you don't have Pluralsight membership, I encourage you to get one this year because it allows you to access their 5000+ online courses on all the latest topics like front-end and back-end development, machine learning, etc. It also includes interactive quizzes, exercises, and the latest certification material.

It's more like Netflix for Software Developers and Since learning is an important part of our job, Pluralsight membership is a great way to stay ahead of your competition.

They also provide a 10-day free trial without any commitment, which is a great way to not just access this course for free but also to check the quality of courses before joining Pluralsight.

When to use 64-bit JVM?

If you are running on a 64-bit architecture with a 64-bit Operating system, like Windows 10, it makes a lot of sense to use 64-bit JVM to run Java applications like Minecraft, Eclipse, or Netbeans.

It will reduce garbage collection frequently and allow you to allocate more memory to your Java process, thus preventing java.lang.OutOfMemoryError: Java heap space.

7) The garbage collector will take more time to do the cleanup, so full garbage collection will have longer pause time.

8) Client JVM is only available for 32-bit JVM and not for 64-bit

9) Some features are not available for 64 bit Java on the Windows platform. Ex., Sun PKCS#11 provider is not supported on 64-bit Windows platforms due to the lack of suitable PKCS#11 libraries

10) There’s also Azul’s C4 pauseless collector, which can cope with huge heaps.

That's all about the difference between 32-bit and 64-bit JVM in Java. As you have seen, the key difference comes in how much memory you can allocate, while 32-bit JVM can just have 4G which is very less for modern, memory-intensive Java application, 64-bit JVM virtually gives you unlimited memory.

This also affects garbage collection pauses because if the heap is bigger than obviously, GC will take more time to clean it up but the idea is to avoid GC and have enough memory to sustain until the restart happens.  I have mentioned a couple of good courses in the article, in case you want to learn more and here is also a book if you like to read.

Further Learning
Java Memory Management (Udemy)
Understanding Java Virtual Machine (Pluralsight)
The Definitive Guide of Java Performance (book)

Other Java Programming Articles you may like

Thanks for reading this article so far. If you like this article then please share it with your friends and colleagues. If you have any questions or feedback then please drop a note.

P. S. S. - If you need more courses on Java Performance, I also suggest you check out  Java Multithreading, Concurrency, and Performance Optimization by Michael Pogrebinsky on Udemy, I just loved this course and I highly recommend anyone who wants to learn a high-performance Java application. 

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