Abit AT7 User Manual page 45

Introducing the BIOS
DRAM Clock/Drive Control:
This item can let you set several items concerning the DRAM parameters. If you do not understand what
each item does, please keep the default settings. Wrong settings may cause system unstablity, data loss or
even prevent boot up!
Current FSB Frequency:
This item will show you the current system front side bus speed.
Current DRAM Frequency:
This item will show you the current DRAM bus speed.
DRAM Clock:
Four options are available: 100 MHz ( 133 MHz ( 166 MHz ( By SPD. The default setting is By
SPD. You can set the DRAM running speed, but if your DRAM module does not support the set speed,
the system may be unstable or un able to boot up! If you set to "By SPD", the BIOS will read the DRAM
module SPD data and automatically set the DRAM running speed to the value stored in it.
SPD (Serial Presence Detect) is a feature available on a number of SDRAM/DDR SDRAM DIMM
modules that solves industry-wide compatibility problems by making it easier for the BIOS to
properly configure the system to fit SDRAM performance profiles.
The SPD device is a small serial EEPROM chip that stores various information about the DIMM
module's size, speed, voltage, drive strength, latency timing and the number of row and column
addresses. When the BIOS reads these parameters during POST, it automatically adjusts the values in
the CMOS Advanced Chipset Features screen for maximum reliability and performance.
Figure 3-5B. DRAM Clock/Drive Control Screen
What's SPD?
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User's Manual