Michael Muchmore reports for PC Magazine:

In brief, here are the major changes—known for sure—in Apple’s next OS X:
• Built-in support for Microsoft Exchange servers
• A 64-bit kernel and drivers
• Reduced system requirements—that is, a smaller memory and disk footprint
• A new lightweight version of QuickTime that supports more video formats, called QuickTime X
• Grand Central, a technology that offers better support of multicore processors by all parts of the OS and by third-party developers’ apps
• OpenCL, which lets the OS and apps take advantage of ATI and Nvidia graphics cards’ processors to take some of the burden off the CPU
• Support for Sun’s ZFS open-source file system

Here’s what’s guessed at but not confirmed by Apple or the developer releases:
• No more support for PowerPC processors
• A new “marble” UI theme

Muchmore reports, “The emphasis is largely under the covers, with performance improvements and trimming down the disk and memory footprint.”

“More of the system, including the kernel and drivers, will be native 64-bit. Additionally, usage of multicore processors will be enhanced. A 64-bit system means that Macs will be able to use up to 16TB of memory, though the OS already used techniques to address more than the 4GB limit of 32-bit systems. It also means that all drivers need to be 64-bit. Since Apple itself makes the only PCs that run the OS, that won’t present the difficulties experienced with Microsoft’s move to Vista, which also required all-new drivers from dozens of hardware partners,” Muchmore reports.

“Multicore support uses the new Grand Central technology, which allows every process in the OS, as well as externally developed software, to efficiently divvy out processing to multiple cores, such as those of Intel Core 2 and Quad-Core Intel Xeon processors,” Muchmore reports. “Of interest mostly to IT folk, the new OS X will fully support Sun’s ZFS file system, which allows things like storage pools, snapshots, dynamic striping, and ‘Adaptive Endian-ness’ (meaning it can support mixed platforms that use opposite byte orders).”

Muchmore reports, “The last known major under-the-hood performance improvement is that the new OS will be able to harness the power latent in most computers’ graphics processors, using OpenCL, or ‘open computing language.’ The technology was proposed by Apple to AMD, Nvidia, and Intel… The technology won’t affect everyday apps like word processing, but it should speed up video and image manipulation. Of course, you need a graphics card with an OpenCL driver for it to work. Apple will surely supply this on new machines.”

There is, naturally, much more in Muchmore’s full article here.