System Speed Control

With some motherboards, all of the CPU and Voltage settings are controlled via the CMOS rather than via a series of jumpers on the motherboard. In fact, most boards on the market today do it this way. Only the older boards still have you set the processor settings via jumpers. the placement of these options varies from BIOS to BIOS. Sometimes they are spread out all around the setup utility. Sometimes they are all grouped together in their own menu. However it is laid out in your BIOS, let’s go over some of these settings:

• System Performance
  Some boards have an overall option to change the settings in a global fashion to increase speed. Normal would be the default setting, with FAST and TURBO being additional options.
  
• CPU Frequency Select
  This is where you set the front side bus speed for your system. The available options depend on the speeds supported by your motherboard, but 100MHz and 133 MHz are pretty standard options today.
  
• Frequency Stepping
  Most better motherboards allow you to increase the front side bus speed in increments. Commonly, you can increase the speed in 1 MHz increments. So, if you set the above setting to 100 MHz, then you can use this setting to increase it to 101, 102, 103, and so on. This is great for overclockers who require a fine-tuned control over the FSB speed in order to max out their available speed.
  
• DRAM Clock
  This allows you to control the speed at which the DRAM operates. The default setting is typically BY SPD. The SPD is the serial presence detect mechanism of the DIMM. This feature became standard on DIMMs after the advent of PC100. It is an EEPROM on the corner of the DIMM that holds all of the specs necessary to run the module. By having the BIOS determine memory settings BY SPD, it uses this EEPROM as the reference and automatically fine tunes settings to work to the specs demanded by the module. There are reasons why you might not want to just fall back on the SPD setting, including the fact that the manufacturers don’t always get it accurate when they program the EEPROM. So, many people override the setting with the manual options, and set the speed manually according to the bus speed.
  
• CPU Ratio Select
  This is where you select the multipler at which your processor operates. Most boards support a variety of multipliers.
  
• CPU Voltage Select
  Allows the user to control the voltage delievered to the CPU core. Most users will not fool with this, but overclockers very well may as they fine tune the voltage to aid in speed and stability of an overclocked processor.
  
• DDR Vcore Select
  Adjusts the voltage delivered to the DDR memory.
  
• AGP Voltage Adjust
  Adjusts the voltage sent across the AGP port to the video card.
  
• C.I.H. 4-Way Protection
  The actual defintion of this varies from board to board, but basically it is a protection machanism to protect your BIOS for being written by a virus or some other nasty program that is trying to corrupt your BIOS. If this is enabled, only a BIOS specific update utility will be permitted to write to the BIOS. This utility would be used to flash the BIOS.

DRAM Control

If the DRAM clock is set manually, you will have a few other options to take note of and define:

• CAS Latency
  CAS Latency is a measure of latency of a memory chip. CAS stands for Column Access Select. Basically, it is a measure of how long it takes from when an initial READ command is sent to memory to when the first piece of the resulting data is output. The measurement is done in clock cycles, so a CAS Latency of x means that a READ command sent to memory at clock cycle c will result in data output starting at clock cycle c + x. In short, CAS3 is the standard latency for memory modules, because it is cheaper to manufacture. If the CAS spec is not mentioned or defined, it is probably CAS3. CAS2, though, is a faster memory module. The latency is less, and this leads to faster application speeds. As you might expect, such memory is typically more expensive. If you are using CAS2 memory and it is enabled as such in the BIOS, you might notice a bit of a speed increase. Even with CAS2 memory, though, it could be necessary to choose CAS3 in your CMOS in order to make the memory stable in a higher bus-speed compter. Some BIOS versions default to CAS 2.5.
  
• Bank Interleave
  This feature enables you to set the interleave mode of the SDRAM interface. Interleaving allows banks of SDRAM to alternate their refresh and access cycles. One bank will undergo its refresh cycle while another is being accessed. This improves performance of the SDRAM by masking the refresh time of each bank. A closer examination of interleaving will reveal that since the refresh cycles of all the SDRAM banks are staggered, this produces a kind of pipelining effect. Whether you set this option to 2-bank or 4-bank is determined by the type of DRAM you have and how many banks are on your DIMMs. Most DRAM in use today (sticks 64 MB of higher) are 4-bank, so setting this option to 4-bank is usually right. If you are unsure, you can look up the specs of your DRAM. Otherwise, just disable the option.
  
• DRAM PreChrg to Act CMD: Setup the minimum row precharge time.
  The Choice: 2T, 3T.
  
• DRAM Act to PreChrg CMD: Setup the minimum RAS pulsewidth.
  The Choice: 5T, 6T.
  
• DRAM Active to CMD: Setup the minimum CAS to RAS delay.
  The Choice: 2T, 3T.
  
• DRAM Queue Depth:
  The Choice: 4 level, 2 level, 3 level.
  
• DRAM Drive Strength: Setup the DRAM’s driving current strength.
  The Choice: Auto, Manual.
  
• DRAM Command Rate: Setup the timing at each cycle.
  The Choice: 1T Command, 2T Command.