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36 Intel Server Board S845WD1-E Product Guide
Table 10. PCI Bus Configuration IDs (continued)
IDSEL Value Device
30 ATA-100 controller Promise Technology PDC20267
31 ATI Rage XL Video Controller
PCI Arbitration
The PCI bus supports six PCI masters (ATI Rage XL, two Intel 82550s, Promise ATA-100
Controller, PCI connector 1 and an arbiter (PCI connector 2 and PCI connector 3). All PCI masters
must arbitrate for PCI access, using resources supplied by the ICH2. The host bridge PCI interface
(ICH2) arbitration lines REQx and GNTx are a special case in that they are internal to the host
bridge.
ATA-100
The S845WD1-E server board provides an embedded dual channel ATA-100 bus through the use
of the Promise Technology PDC20267 ASIC. The PDC20267 ATA-100 controller contains two
independent ATA-100 channels that share a single 32-bit, 33-MHz PCI bus master interface as a
multifunction device, packaged in a 128-pin PQFP.
The ATA-100 controller supports the following features:
• The scatter / gather mechanism supports both Direct Memory Access (DMA) and
Programmable I/O (PIO) IDE drives and ATAPI devices.
• Support for ATA and ATAPI proposal PIO Mode 0, 1, 2, 3, 4, DMA Mode 0, 1, 2, and
Ultra DMA Mode 0, 1, 2, 3, 4, 5.
• The IDE drive transfer rate is capable of up to 100 MB/sec per channel.
• The host interface complies with PCI Local Bus Specification Revision 2.2.
• 32-bit, 33-MHz bus speed and 132 MB/sec sustained transfer rate.
The Promise PDC20267 supports IDE RAID through dual ATA-100 Channels. In a RAID
configuration, multiple IDE hard drives are placed into one or more arrays of disks. Each array is
seen as an independent disk, though the array may include upwards of two, three, or four drives.
The IDE RAID can be configured as follows:
• RAID 0: Striping one to four drives.
• RAID 1: Mirroring two drives.
• RAID 1 +: Spare drive (three drives).
• RAID 0 +: One to four drives are required.
RAID 0 configurations are used for high-performance applications, as it doubles the sustained
transfer rate of its drives. RAID 1 configurations primarily used for data protection. It creates an
identical drive backup to a secondary drive. Whenever a disk write is performed, the controller
sends data simultaneously to a second drive located on a different data channel. With four drives
attached to dual ATA-100 channels, two striped drive pairs can mirror each other (RAID 0+1) for
storage capacity and data redundancy.