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64 Bit CPU's - Better or Just Bigger?

Now that AMD is coming out with a 64-bit CPU (the Athlon 64) for the desktop, and their 64-bit Opteron chip is already in use on servers along with Intel’s 64-bit Itanium and Itanium II, our technical support people are starting to hear questions about 64-bit processors. Most of these questions fall into one of two camps, and we’ll take the easier one first.

1. Will Microscope identify and test the 64-bit processors from AMD and Intel? The answer to this is a qualified Yes, and we’ll have more to say about it later in the tip.

2. Would it be worth it to upgrade to a 64-bit CPU? The short response to this one is: probably not just yet, but like most short responses it really deserves more information.

This 64-bit architecture promises a tremendous increase in computing power and speed, but to put it in proper perspective we should take a look at the similar jump in technology that occurred in 1985, going from the 16-bit 286 to the 32-bit architecture used since then. And to fully understand that, we should look at what it means when we say a processor has a certain number of ‘bits’.

Every CPU from the 386 to the latest Pentium and Athlon processors has used a 32-bit architecture, which means that the internal registers of the CPU are 32 bits wide. In other words, 32 bits of data are the most the CPU can handle on a single instruction cycle, and a block of data that size is considered to be one ‘word’ of data for that CPU. A ‘word’ not only determines the size of a program instruction, but also the maximum size of a RAM location that the CPU can address. This turns out to be 4,294,967,295, which means that a 32-bit architecture can use a maximum of 4 GB of RAM. By comparison, a 64-bit architecture can address 16 exabytes (16 billion GB) of RAM.

Now, many of us are still deciding whether to upgrade our desktop systems to 512 MB or 1 GB of RAM, which is only a fraction of their current capacity, so the opportunity to multiply that a few billion times may not hold much appeal. However, doubling the size of the CPU’s instructions also provides a quantum leap in processing, especially for mathematics and in rendering 3-D graphics. Anyone in the scientific or gaming communities will immediately understand the advantages.

There is a catch, however. In order to get the most from this additional power, the motherboard, operating system and applications must all be designed for it. Windows 95 was the first OS that provided 32-bit power for desktop PCs, and it showed up a full decade after the 86 chip. The delay won’t be so great this time because Windows XP 64 is already in development, but you won’t see gains in your desktop computing until the OS and your computing-intensive applications are available in 64-bit versions.

In fact, in a 32-bit system the Itanium chips actually come in slower on some benchmarks than the Pentium IV, because they are not running in their native mode. The new Athlon chip was designed to be backwards compatible, so there won’t be any penalty there, except of course the higher cost. In a server things are different, because you can get the entire platform built around an Itanium or Opteron chip, and servers are one area that can really benefit from the extra power.

So, let’s take another look at our questions. When I used the word ‘qualified’ in the Microscope question, that’s because no diagnostic, including Microscope, comes yet in a 64-bit version, and until it does it will not really test the full capabilities of a 64-bit processor. That’s also true of our competitors, regardless of their advertising claims.

On the next question, should you run out and buy a 64-bit CPU? For your server, maybe. For your desktop, if you are into games, video editing, weather modeling or huge spreadsheets, you’ll probably want to jump on this bandwagon just as soon as the hardware and software are available at a reasonable price. For those of us who use our systems for word processing and e-mail, there’s no rush at all. At some point anything 32-bit will be considered legacy technology and it will be easier to upgrade than to fight the trend, but that’s a few years away.

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