By Katie Marsal

Published: 11:00 AM EST

Versions of Apple's $999 Intel-based Developer Transition Kit began arriving on the doorsteps of several Mac OS X developers earlier this week, offering the first material evidence that the company will adopt the two-way serial interface known as PCI-Express in future Macs.

According to reports, the systems identify themselves as Apple Development Platform (ADP 2,1) and sport a 3.6 GHz Intel Pentium 4 with 2 MB L2 Cache, 800MHz front-side bus, and 4 DIMM slots -- two of which are occupied by 512MB 533MHz DDR2 Dual Channel SDRAM modules for a total of 1GB of SDRAM.

Sources said the system's graphics card identifies itself as an Intel Graphics Media Accelerator 900 (GMA 900). Some other reports have placed an Intel Graphics Media Accelerator 800 (GMA 800) inside the units. It's unclear if those reports are inaccurate, or if Apple is shipping the systems with slightly varying specs.

Perhaps the most interesting aspect of the development systems is their PCI layout, which implies that Apple will likely adopt the PCI-Express interface by the time it ships its first Intel Macs. In addition to two vacant 33 MHz, 32-bit PCI slots, the systems pack a single 1X PCI-Express slot and a single 16X PCI-Express slot -- the latter of which comes occupied by a Silicon Image Orion ADD2 card offering DVI-D compatibility.

For its drive interface, sources say the development systems include a total of 4 Serial ATA (SATA) connectors. Two of the connectors are free, one is wired to a 160GB/7200rpm SATA hard disk drive and the other dangling. A 16x DVD+R DL/DVD±RW/CD-RW optical drive is connected to an ATA chain.

These development-based Intel Macs appear to be shipping in a slightly modified aluminum Power Mac G5 enclosure that sports an altered cooling system consisting of a different fan configuration. Located at the rear of the unit are two USB 2.0 ports, a Gigabit Ethernet connector, and one FireWire 400 port. On the front of the unit developers have access to a headphone jack, one USB 2.0 port, one FireWire 400 Port and a micro switch that comes mounted next to the power switch and can be activated by a paperclip. However, its function is unknown.

Also shipping inside the development kit packages is a keyboard, mouse, power cable, keyboard cable, and Mac OS X 10.4.1 for Intel DVD. Sources so far have reported absolutely no luck in their attempts to boot the included copy of Mac OS X for Intel on other PC systems. In their attempts to do so, they have reportedly been met by error messages stating that the PC hardware configurations are not supported by Darwin -- the underlying UNIX-based foundation to Mac OS X.

Developers who signed up to receive Developer Transition systems are actually renting the $999 hardware from Apple for a period of approximately 18 months. Apple requires that the developers make plans to return the systems to Apple within a week of December 31, 2006.