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Layout
The A7M266 uses a very spacious PCB for a 1/5/1 (AGP/PCI/AMR) configuration. The AMD761 system controller (Nort Bridge) is complemented by the VIA VT82C686B South Bridge featuring ATA/100 support in addition to the additional USB and integrated AC97 integrated sound. In the present form, the A7M266 has only two 184 pin DDR DIMM slots, however, this appears sufficient for the simple reason that hardly any 64 MB DDR DIMMs are in circulation at all and 256 MB system memory should suffice even for Windows2000.
The minimalist AC97 sound is too profane for a high end board and while the C-Media CMI8738 sound chip is an acceptable upgrade it won't qualify as hi-fi solution either. An upgraded version of the A7M2666 also features an integrated 3Com fast Ethernet chip with the RJ45 port added on top of the back panel USB ports, however, the version tested did not have this optional feature. The most negative aspect of the board is the choice to include an AMR, the another minor nuisance is the placement of the core voltage selector jumpers at the left end of the 5th PCI slot making it difficult to reach them, in case manual Vre manipulation is chosen. Very well accessible, though, are the jumpers for V I/O and V I/O1.
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V I/O and V I/O1
V I/O usually refers to the 3.3V supplied to the DIMM slots, here it is referring to the chipset (North Bridge) which, for simplicity reasons, was originally designed to run at the same voltage as the DIMMs (some other chipsets are running at 1.4 or 1.7 V). With the move to DDR and its lower operating voltage of 2.5 V (VDDQ), the voltage regulators needed to be redesigned to provide both a 3.3V (adjustable) and a 2.5 V (adjustable). Therefore, the new nomenclature calls V I/O the chipset voltage and V I/O1 the memory voltage. The jumpers for each setting are in the path of the AGP slot (V I/O) and above the IDE interface (V I/O1). Interestingly, while ASUS adheres to the guidelines for the V I/O voltage of 3.3 (scalable to3.56) V, V I/O1 is set slightly out of specs, that is, the base setting is 2.8V instead of 2.5V with the option increasing it to 2.9V or decreasing it to 2.7V. Most current DDR chips are based on a 0.17µm die process, thus, the internal DIMM voltage is regulated to some 1.8V and only the wave form of the output signal is sharpened. This can speed up the DIMMs but also cause unwanted effects like signal ringing, particularly at low load, that is lower total system memory. On the other hand, some DIMMs still require slightly higher voltage than others.
By factory default, the A7M266 is jumpered over pins 1-2, resulting in a DIMM voltage of 2.8V which causes performance deterioration in most high performance DIMMs. The standard DDR operating voltage can easily be restored by simply removing the jumper.
The drawback is that any excessive voltage can cause thermal runaway or local heat buildup in the memory chips causing their performance to deteriorate quite dramatically. Undocumented in the manual is the option of completely removing the jumper from the V I/O1 header which will bring down the voltage to 2.5V and thus DDR specification. This point will later become extremely important as I will show below.
Back to the layout
Overall there is enough space around the CPU Socket462 to mount even large heatsinks. The only concern are a few smaller capacitors that just clear e.g. the Thermaltake SuperOrb but can make the mounting a bit difficult. As seen on other recent ASUS mainboards, the A7M266 is equipped with a standby power LED to indicate charging of the battery of capacitors as a potential hazardous condition when manipulating or exchanging hardware. Another typical ASUS feature is the integrated ASUS ASIC for hardware monitoring and IRQ management.
Jumpers and dip switches
In general, the A7M can be operated in completely jumperless mode, should the user select to revert to hard jumper configuration of the board, these or the dip switches need to be activated by means of the jumper enable (JEN) jumper, located directly above the ASIC chip. Some of the jumpers were already mentioned above as, e.g., the Vre (VID1-4) and V I/O and V I/O1 jumpers for the different voltage requirements. Other jumpers are used for hard connection of the integrated ethernet and sound chip.
In addition, a four-position dip switch (DSCKF), located to the right of the second PCI slot can be used to select the FSB in steps from 95 MHz (undocumented) to 133 MHz. Again, for most users, there is no point of going this way since the BIOS allows reprogramming of the ICS 94225 linear programmable clock generator in 1 MHz steps.
Since ASUS is using the Award Medaillion BIOS with the safe boot option (default values) in case the board hangs on boot up, the clear CMOS jumper pins are not really necessary and have been omitted. If worst comes to worst, there is always the possibility to remove the battery and to clear the CMOS this way. Keep in mind, though that it is mandatory to disconnect the board from power and discharge the capacitors by pressing the power button until the standby power LED goes off. To make the list complete, two jumper headers (USBPWR1 & 2) are used to specify which USB ports can be used for Power-On.
Connectors
Aside from the dedicated chipset heatsink fan, the A7M266 features three additional fan headers for CPU, power supply and additional case fans. In addition there is the full range of additional conncctors, from the extra USB headers over temperature sensor inputs and SMBus monitoring as well as the sound-in, infrared, Wake-On-LAN and Wake-On-Ring. A proprietary ASUS feature is the ASUS iPanel header for external display of hardware monitor read-out.
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