Asus PCI-DA2100 User Manual - Page 307

ASUS GUI RAID Manager: Array Management assigned as the default value for host channels, and 7 for drive channels. ♦ Default Sync Clock (MHz), Default Xfer Width. These parameters set the data transfer clock rate for synchronous communication over the SCSI bus, and enable or disable wide transfer, respectively. For a detailed description of these parameters, see the discussion below. Data that is transferred across the SCSI bus in synchronous transfer mode is clocked using a synchronous transfer clock signal. The frequency of this signal determines the rate at which data is transferred. If, for example, the synchronous transfer clock is 10 MHz, data transfer rate will be 10 million bytes per second (assuming narrow transfer). Data transfer across the SCSI bus can be either 8 bits or 16 bits at a time. The former is referred to as narrow" transfer, while the latter is referred to as wide" transfer. At the same synchronous transfer clock rate , data transfer rate using wide transfer will be double that using narrow. With synchronous transfer clock of 10 MHz, data transfer rate will be 10 Mbytes/second under narrow transfer, and 20Mbytes/second for wide. Occasionally, under conditions in which SCSI signal quality is poor, such as long cables, poor connections, or bad termination, it may be necessary to reduce the synchronous transfer clock to allow the SCSI channel to function normally. Under worst conditions, it may be necessary to switch to asynchronous communication mode. Furthermore, certain older SCSI devices may only support narrow transfer and behave abnormally when an attempt to negotiate wide transfer is made. Under such conditions, 4.6 Setting Channel Configuration 4-15