The 64-Bit Question

Continued from page 2

By Simson Garfinkel

June 2, 2004

It wasn't until the 32-bit machines in the field vastly outnumbered the 16-bit ones that Microsoft starting shipping its first real 32-bit operating system-Windows 95. By that time Intel had brought out two more generations of x86-based machines-the 80486, and the Pentium.  Yes, Microsoft could have delivered a 32-bit operating system years before Windows 95 shipped. But doing so would probably have been a mistake: why sell an operating system that won't run on the majority of PCs out in the marketplace?

All of this history is suddenly relevant once again as we consider the next big jump in PC architecture-the shift from 32-bit to 64-bit computing. But while the payoff moving from a 16-bit address space (or 20-bits, if you consider the 8088's segmented architecture) to 32 bits was huge, the move from 32 bits to 64 bits will barely be noticed by most computer users. The reason is that 32 bits is actually large enough to solve the vast majority of computing tasks-not just today's, but also tomorrow's.

The move from 32 bits to 64 is unlikely to bring the same sort of quantum jump in speed or capabilities that we got moving from 16 bits to 32. Yes, 64 bits of address is truly humungous, but 32 bits is nothing to sneeze at.

Today there are few applications that really need more than 4 gigabytes of memory. If what you are doing is word processing, spreadsheets, e-mail, and Web browsing, 32 bits is going to provide enough address space for the conceivable future. My Windows desktop computer is a memory hog-its copy of Internet Explorer routinely bloats up to 64 megabytes. But that's still one sixty-fourth the size of the machine's 4 gigabyte memory map. I can't imagine that I could run a Web browser that would require a 4 gigabyte memory map: it would take nearly 10 hours just to download that much information over my DSL line!

You might think that multitasking with other, similarly oversized applications would cause ever-increasing memory pressure, to the point where one does become concerned about address space usage. But that's not the case. Windows, Unix, and other modern operating systems use a technique called virtual memory to give each program its own isolated memory map. On a 32-bit computer this means that every running program  gets its own 4 gigabytes of virtual memory to play around with. So while a single instance of a running program can't access more than 4 gigabytes, a 32-bit machine running Windows XP with 10 or 20 gigabytes of memory would have no trouble sharing that memory between a bloated browser, a bloated copy of Word 2003, and a bloated copy of Access.

Where that 64-bit address space makes the big difference is when a single program needs to access more than 4 gigabytes of memory at once. For example, if you are running a data warehouse for a multinational corporation with 10 terabytes of online storage, your database server might seriously benefit by having 10 or 20 gigabytes of index files stored in memory. A large-scale simulation could similarly benefit by having lots of RAM at the disposal for doing things like modeling the weather for the day after tomorrow.

With companies like Dell shipping home computers with 512 megabytes of RAM, and Windows XP computers routinely using 1.5 gigabytes of memory to hold all of their programs, the marketers pushing 64-bit computing are going to be saying that you need a 64-bit machine to break through the quickly approaching 4-gigabyte limit. Don't believe it. In fact, Dell already sells 32-bit computers with 8, 16, and 32 gigabytes of RAM. The marketers want you to buy 64-bit machines because these systems cost more.