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BIOS Tuning Guide

By: Asher Moses | Guides | Posted: Feb 26, 2002 5:00 am

- Advanced Chipset Features



CAS Latency Time - The CAS Latency option controls the time delay that passes before the memory carries out a command. Simply put, the lower the CAS Latency selected, the more performance you will be getting because the memory will carry out tasks quicker. However, not all memory modules will support such high speeds. Start off by setting it to 2 and if you experience instability, kick it up to 3.


Active to Precharge Delay - This determines the amount of CPU cycles that active data can accumulate before the ram is purged. For optimal performance, set this to "auto".


DRAM RAS# to CAS# Delay - This option selects the time delay between the Row Address Strobe (RAS) and Column Address Strobe (CAS) signals. Obviously, the lower the delay, the better the performance.


DRAM RAS# Precharge - This is where you can select the number of CPU clocks allocated for the RAS (Row Address Strobe) signal to accumulate its charge before the DRAM is refreshed. If insufficient charge is applied, refresh may be incomplete which could cause data loss. For optimal performance, set this to "2".


Refresh Mode Select - The "Refresh Mode" is the speed at which each of the rows in the DIMM are refreshed. With 128Mbit DIMMs, because they contain 4096 rows, can refresh each row at 15.6 µsec. This is worked out using the formula 64,000 µsec / 4096 rows = 15.6 µsec. 64,000µsec (64msec) being the speed at which memory cells need to be refreshed. From this information we can say that because a 256Mbit DIMM has 8192 rows, the refresh time is halved, because there are twice as many rows to be refreshed in the 64,000µsec time period, equaling 7.8µsec. Increasing the Refresh Mode will give higher performance because it is wasting less bandwidth. This means power consumption is reduced as well.


DRAM Read Thermal Management - This is a new Intel i845 feature that monitors DRAM temperatures and reduces the aggressiveness of the DRAM timings. This results in cooler DDR SDRAM but a slower memory performance. For optimal performance, disable this option.


Delayed Transaction - It is a well known fact that the ISA bus is significantly slower than the PCI bus. When enabled, delayed transaction frees the PCI bus from slow ISA accesses by allowing the PCI device to write to an integrated 32bit buffer while an ISA device is occupying the system bus. If you use ISA devices in your system, make sure you enable this setting.


AGP Aperture Size (MB) - This is the amount of main memory that is allocated to the AGP device. Using this function the AGP card can process data from the main memory itself, instead of onboard memory. It is important to select the AGP Aperture Size wisely because too much will cause lack of memory for other operations and too little will give low graphic performance. The AGP aperture size should be set to half, or a quarter of your system memory. So, if you have 256MB system memory you should set your AGP aperture size to either 128MB or 64MB.


Delay Prior to Thermal - This is for the Pentium 4 only and is used when the CPU overheats. Setting this option to either 4 min, 8 min or 16 min is the time elapsed before the system will allow the CPU to throttle back up to full power. Optimal setting is 16 minutes.


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