Inside Atom Architecture

Chipset

Depending on the model, Atom can be paired either with an Intel 945-class chipset (Atom 2xx and N2xx) or with the new Intel US15W (Atom Z5xx), also known as “Intel System Controller Hub” or simply SCH. It is interesting to note that Intel has granted a license to SiS to design chipsets targeted to Atom CPUs, so you may see in the future Atom CPUs using chipsets from this manufacturer.

Since Intel 945 chipsets use two relatively big chips, CPUs using these chipsets are targeted to laptops only, as they can’t fit the small footprint required for smaller applications. In theory any Intel 945 chipset can be used, but Intel recommends the mobile version and you will probably see products with Intel 945GSE, which is the chipset recommended for the “NetBook’08” platform. All memory and I/O features for a small laptop based on Atom CPU will depend on the chipset used.

The new US15W chipset, on the other hand, is a very small single-chip solution, allowing Atom CPUs to be used on handheld devices with internet access. It uses a completely new design and some of its main features are:

• Graphics engine with full hardware-based HD video decoder (supporting H.264, MPEG2, MPEG4, VC1 and WMV9 decoding) and 3D graphics capability, running at 200 MHz (Intel Graphics Media Accelerator 500, which is a DirectX 9.0c/Shader 3.0 engine)
• Support for two displays, one internal to the device and one external. They can work as two independent displays or showing the same image at the same time (cloning). The connection between the chipset and the internal LCD display is done through an LVDS (Low-Voltage Signaling Interface) supporting 18- or 24-bit colors, while the connection between the chipset and the external video monitor is done through a SDVO (Serial Digital Video Out) link; this link can be easily converted to any standard output (VGA, S-Video, DVI, HDMI, etc) through an external chip.
• Supports DDR2-400 or DDR2-533 memories up to 1 GB, single-channel (the foil in Figure 3 shows a wrong maximum memory capacity)
• HD Audio controller with 32-bit resolution and up to 192 kHz sampling rate. The actual audio quality will depend on the audio codec used
• Eight USB 2.0 ports
• Two x1 PCI Express lanes
• One ATA-100 port
• Three SDIO ports

Figure 3: Intel US15W chipset main features.

Figure 4: Intel US15W block diagram.

One very interesting thing to notice is that this chipset does not support SATA ports. This was done on purpose, because according to Intel when they were developing this chipset 1.8” hard disk drives were available only with parallel ATA (PATA) interface, not SATA. They also think that mobile internet devices will use SSD (Solid-State Drives) in the near future, not hard disk drives.