64 Bit Computing


The Itanium can load instructions and data onto the CPU before they're actually needed or even if they prove not to be needed, effectively using the processor itself as a cache. Presumably, this early loading is done when the processor is otherwise idle. The advantage gained by speculation limits the effects of memory latency by allowing loading of data before it is needed, thus making it ready to go the moment the processor can use it.        


What is 64-bit computing?

The labels "16-bit," "32-bit" or "64-bit," when applied to a microprocessor, characterize the processor's data stream. Although you may have heard the term "64-bit code," this designates code that operates on 64-bit data.

AMD's 64-bit platform

To access an area in the computer's physical memory (RAM) to store or retrieve data, the processor needs the address of that location, which is an integer number representing one byte of memory storage. Suddenly, having 64-bit registers makes sense as, while a 32-bit processor can access up to 4.3 billion memory addresses (232) for a total of about 4GB of physical memory, a 64-bit processor could conceivably access over 18 petabytes of physical memory. This is the one area that clearly shows why 64-bit processors are the future of computing, as demanding applications such as databases have long been scraping on the 4GB memory ceiling.

Dynamic range

The main thing that a wider integer gives you is increased dynamic range. In the base-10 number system to which we're all accustomed, you can represent a maximum of ten integers (0 to 9) with a single digit. This is because base-10 has ten different symbols with which to represent numbers. To represent more than ten integers you need to add another digit, using a combination of two symbols chosen from among the set of ten to represent any one of 100 integers (00 to 99). The general formula that you can use to compute the number of integers (dynamic range, or DR) that you can represent with an n-digit base-ten number .


With this article and the previous one, that mention the 64-bit architectures by Intel and AMD, we finished to talk about the processors for the beginning of the millennium. In addition, it is important to mention that there already are computers running 64-bit versions of Windows and Linux. Now, more than performance, our biggest concern is the compatibility with our present programs. We really have to verify how much those 64-bit architectures are compatible with our 32- or 16-bit programs. We hope that in less than a year we already have the answer to this question.