Lesson 3. Porting code to 64-bit systems. The pros and cons

• Application life-cycle
• Application performance requirements
• Using third-party libraries in a project
• Dependence of third-party developers upon your libraries
• 16-bit applications
• Assembler code
• Toolkit

You should begin studying 64-bit systems with the question "How much rational it will be to recompile a project for a 64-bit system?". You must answer this question but take your time and think it over. On the one hand, you might lag behind your rivals failing to offer 64-bit solutions on market. On the other hand, you might waste your time developing a 64-bit application that will have no competitive advantages.

Here are some factors that will help you make a choice.

Application life-cycle

You should not create a 64-bit version of an application with a short life-cycle. The WoW64 subsystem allows obsolete 32-bit applications to work rather well on 64-bit Windows systems. It is unreasonable to make a program 64-bit if you stop maintaining it in 2 years. The practice shows that the move to 64-bit Windows versions will be very slow and smooth. Perhaps most of your users will use only the 32-bit version of your program solution in the nearest future. You should keep in mind that this course was written in 2009 when most users were working with 32-bit versions of operating systems. But in time 32-bit programs will look more and more unnatural and outdated.

If you plan a prolonged development and maintenance of your program product, you should start working on its 64-bit version. Of course you should take your time but keep in mind that the later you have a full 64-bit version, the more problems you are to encounter while maintaining such an application installed on 64-bit Windows versions.

Application performance requirements

After being recompiled for a 64-bit system a program can use huge amounts of memory and its speed will increase in 5-15%. 5-10% of speed gain is achieved due to architectural features of the 64-bit processor, for example, a larger number of registers. And another 1-5% performance gain is determined by the absence of the WoW64 layer that translates calls between 32-bit applications and the 64-bit operating system.

For example, Adobe company says that a new 64-bit "Photoshop CS4" is 12% faster than its 32-bit version".

Applications involving large memory amounts can expect a great performance gain. These are graphical editors, CAD-systems, GSI CAD, databases and packages for modeling various processes. The capability to store all the data in memory and therefore avoid additionally loading them from the hard disk may increase the speed of such applications not in some per cent but in several times.

For example, take Alfa-Bank that integrated an Itanium 2 based platform into their IT-infrastructure. The growth of their investment business had caused the system to fail to manage the increasing load on the current configuration any more: the number of customer support delays sometimes got very critical. The analysis of the situation showed that the bottleneck of the system had nothing to do with processors' performance but it was the limitation of the 32-bit architecture regarding the memory subsystem that allowed using not more than 4 Gbytes of the server address space. The database size was more than 9 Gbytes. It had been used very intensively and that caused a critical loading of the input-output subsystem. Alfa-Bank decided to buy a cluster of two four-processor servers based on Itanium 2 with 12 Gbytes of memory. This decision allowed them to get the necessary performance and fault-tolerance level. As the company representatives say, introduction of Itanium 2 based servers allowed them to eliminate serious issues and manage to save much money.

Using third-party libraries in a project

Before planning the work on developing the 64-bit version of your product, make it out if there are 64-bit versions of libraries and components it employs. You should also find out the pricing policy regarding the 64-bit versions of the libraries. All this you may learn on the site of library developers. If there is no support for the libraries, search for alternative means supporting 64-bit systems beforehand.

Dependence of third-party developers upon your libraries

If you are developing libraries, components or other items intended for third-party developers to create software with, you must be quick in creating the 64-bit version of your product. Otherwise, your customers interested in 64-bit versions will have to search for other solutions. For example, some soft- and hardware security developers appeared to be very late in creating 64-bit programs and it made some of their clients choose other tools to protect their software products.

There is one more benefit of releasing a 64-bit version of a library: you may sell it as a separate product. Thus, your customers who wish to create both 32-bit and 64-bit applications will have to buy 2 different licenses. For example, Spatial Corporation company sticks to such a policy when selling their library Spatial ACIS.

16-bit applications

If your solutions still have 16-bit modules, you must get rid of them. 64-bit Windows versions do not support 16-bit applications.

I should explain one thing here related to using 16-bit installers. They are still used to install some 32-bit applications. There exists a special mechanism that replaces some of the most popular 16-bit installers with their more contemporary versions on the fly. It might make you think that 16-bit programs still work in the 64-bit environment, but it is a mistake, please, keep it in mind.

Assembler code

Do not forget that presence of large assembler code fragments make it much more expensive to create the 64-bit version of an application.

Toolkit

If you have decided to create the 64-bit version of your product relying on the factors mentioned above and are ready to spend time on it, the success is not guaranteed yet. You should have all the necessary tools for that and here you might encounter some very unpleasant things.

The most obvious yet most serious problem is absence of a 64-bit compiler. When we were writing this text (2009) there was no 64-bit C++ Builder compiler by Embarcadero yet. Its release was expected by the end of 2009. You cannot evade this problem unless you rewrite the whole project employing, for example, Microsoft Visual Studio. But while everything is clear in case of compiler absence, other similar issues might be not so obvious and occur only at the step of porting the project to a new architecture. You should make a research beforehand to find out if you can get all the necessary components to implement the 64-bit version of your product. You might face unpleasant surprises.

While making a decision, please keep in mind the last very important factor we have not mentioned here: the price of modifying your program code to compile it in the 64-bit mode. We will tell you how to estimate this price in one of the following lessons. It may be very high and must be considered in planning and scheduling.

The course authors: Andrey Karpov (karpov@viva64.com), Evgeniy Ryzhkov (evg@viva64.com).

The rightholder of the course "Lessons on development of 64-bit C/C++ applications" is OOO "Program Verification Systems". The company develops software in the sphere of source program code analysis. The company's site: http://www.viva64.com.