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BIOS
The K7S5A BIOS is made by AMI with all known shortfalls and advantages. With regard to the advantages, the major plus is the faster POST speed of the board. Disadvantages include incorrect labels, even at POST, e.g. the memory is described as NVRAM (non-volatile RAM) which would be true for the BIOS chip but certainly not for the SD (or DDR) SDRAM. For the greatest part, the BIOS GUI follows the standard layout with yellow lettering on blue screen and offers a few tweaks.
Settings that are accessible include CAS latency (SPD, 2, 2.5, 3T), tRAS, and tRP (3, 4T). Interestingly, the BIOS does not discriminate between SDRAM and DDR, so it is possible to set CAS to 2.5 with SDRAM and to 3 with DDR, keep in mind though, that these settings are not workable and will enable the higher latency for both memory types.
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The mystery settings are in the form of Timing Setting Mode for DRAM, that is Safe, Normal, Fast and Ultra, however, without datasheet it is impossible to tell what these settings enable. The settings are, however, workable and do have an impact on performance as well as on stability, depending on the memory type and overall density used.
Briefly, Nanya, IBM and Micron based DIMMs worked at 128 MB density even in dual (2 DIMMs) configuration at 133 MHz and Ultra settings. Using 256 MB Crucial DIMMs, the system would hang at POST when the Ultra setting was enabled but worked without problems at the Fast setting. The same pattern occurred using 128 / 256 MB Corsair PC2400 DIMMs (Micron chip-based). Interestingly, 512 MB Infineon-based unbuffered DIMMs had no problems at the Ultra setting. On a sidenote, Registered ECC Modules were not recognized at all by the system and only resulted in the known sequence of beeps for memory failure.
In addition, the BIOS main screen shows the options Load Optimal Settings and Load Best Performance Settings, which are even more obscure than the Timing Setting Mode in that no visible changes within the accessible BIOS parameters could be determined.
CPU PnP Setup
More adequate would be the title CPU monitor since the only parameter that can be changed is the FSB. Interestingly, the BIOS settings allow running the memory in +PCI-frequency mode for selected settings (100/133, 133/166) which can be taken as a look ahead statement of SIS towards their committment to the upcoming DDR333 standards Unfortunately, the system would not boot with any of the DIMMs at the 133/166 MHz setting, even when the slowest timing parameters were enabled. I cannot blame it on the memory since the same DIMMs (Crucial Corsair, Nanya and Mushkin) run without problems up to 175 MHz and beyond. All other settings for multipler and voltages are read-only. Some of the readout is duplicated in the Hardware Monitor section of the BIOS.
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