The long wait for 64-bit PC software continues

By Michael Lasky - Windows Secrets

Even though 64-bit PCs have been available for seven years, the promise of 64-bit computing has been delayed by a dearth of 64-bit software.

The situation is improving — slowly — but many major PC applications remain 32-bit affairs.

Microsoft likes to boast about the extra performance delivered by the 64-bit versions of Windows. Likewise, PC vendors continue to pitch the benefits of 64-bit PCs over their 32-bit brethren.

That's all well and good — and theoretically true — but without software optimized for 64-bit machines, using those more-advanced processors for everyday tasks is like running a Formula One race car on regular gas.

The primary difference between 32-bit applications and their 64-bit counterparts is the size of memory the programs can address. Computers use only two digits (ones and zeros), so a 32-bit program can track 2^32 (2 to the 32nd power) memory addresses — about 4GB. This is the basis of the "4GB memory limit" for 32-bit hardware and software.

A 64-bit PC can track 2^64 addresses, yielding a theoretical memory ceiling of about 16 exabytes — 16 billion gigabytes. Of course, no PC can hold that much physical memory — but the point is, they could. Similarly, 64-bit software is capable of managing truly huge data sets.

The 64-bit flavor of Windows takes advantage of this. For example, the 64-bit version of Windows 7 Ultimate can address up to 192GB of RAM. More prosaically, 64-bit Windows can routinely allocate up to 4GB (and sometimes more) to each software process running on the PC. In contrast, 32-bit Windows XP maxes out at 2GB per process.