Abit KR7A, User Manual

Page: 43 / 104

Introducing the BIOS
User’s Manual
3-15
What’s SPD?
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.
Without SPD, the BIOS (or user) must make assumptions about the DIMM’s parameters. Many users
have found that their system will not boot if they are using non-SPD SDRAM DIMMs. As SDRAM
and DDR SDRAM DIMM’s is running at very fast clock speed and there is less room for error. An
incorrect BIOS assumption about an SDRAM and DDR SDRAM DIMM’s parameters can have
serious consequences (e.g. failure to boot or fatal exception errors).
DRAM Timing:
Two options are available: Manual or Auto. The default setting is Manual . When set to “Auto”, the BIOS
will read the DRAM module SPD data and automatically set to the values stored in it. If you set to
“Manual”, the following five items will be available to let you make adjustments.
"
DRAM CAS Latency:
Two options are available: 2 and 2.5. The default setting is 2.5 . You can select SDRAM CAS
( C olumn A ddress S trobe) latency time according your SDRAM specification.
"
Bank Interleave:
Three options are available: Disabled
)
2-Way
)
4-Way. The default setting is Disabled .
Depending on your SDRAM module structure, the 4-Way setting can offer the best performance. If
you choose the wrong setting, the computer system will not run in a stable manner. For detailed
information on your SDRAM module, please ask your SDRAM module manufacturer.
"
Precharge to Active (Trp):
Two options are available: 2T or 3T. The default setting is 3T .
Trp timing value (Precharge time – time from precharge command to when back can be activated).
"
Active to Precharge (Tras):
Two options are available: 5T or 6T. The default setting is 6T .
Tras timing value = Minimum bank active time from activate to precharge of same bank.
"
Active to CMD (Trcd):
Two options are available: 2T or 3T. The default setting is 3T .
Trcd timing value = RAS to CAS latency
+
rd/wr command delay
DDR DQS Input Delay:
Two options are available: Auto or Manual. The default setting is Auto . If you set to “Manual”, then the
next item will be available.