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Advanced CMOS Setup


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Advanced CMOS Setup


May vary according to your system, BIOS version and brand. Some functions may not be present or the order and name may be different (particularly for different BIOS brand). Know EXACTLY what you are doing. Some configurations may keep your computer off from booting. If that's the case: Switch the power off. Turn your computer on WHILE keeping the DEL key pressed. This is supposed to erase the BIOS memory. If it still doesn't boot, consult your motherboard manual. Look for a 'forget CMOS RAM' jumper. Set it. Try it again. If it still doesn't boot, ask a friend or post to a computer hardware newsgroup. You are permitted to panic.

  • Typematic Rate Programming: Disabled recommended. It enables the typematic rate programming of the keyboard. Not all keyboards support this! The following two entries specify how the keyboard is programmed if enabled.
  • Typematic Rate Delay (msec): 500 ns recommended. The initial delay before key auto-repeat starts, that is how long you've got to press a key before it starts repeating.
  • Typematic Rate (Chars/Sec): 15. It is the frequency of the auto-repeat i.e. how fast a key repeats.
  • Above 1 MB Memory Test: If you want the system to check the memory above 1 MB for errors. Disabled recommended for faster boot sequence. The HIMEM.SYS driver for DOS 6.2 verifies the XMS (Extended Memory Specification), so this test is redundant. It is thus preferable to use the XMS test provided by HIMEM.SYS since it is operating in the real environment (where user wait states and other are operational).
  • Memory Test Tick Sound: Enabled recommended. It gives an audio record that the boot sequence is working properly. Plus, it is an aural confirmation of your CPU clock speed/Turbo switch setting. An experimented user can hear if something is wrong with the system just be the memory test tick sound. Since systems have now much more memory than before, this setting is not common anymore.
  • Memory Parity Error Check: Enabled recommended. Additional feature to test bit errors in the memory. All (or almost all) PCs are checking their memory during operation.Every byte in memory has another ninth bit, that with every write access is set in such way that the parity of all bytes is odd. With every read access the parity of a byte is checked for this odd parity. If a parity error occurs, the NMI (Non Maskable Interrupt), an interrupt you mostly cannot switch off, so the computer stops his work and displays a RAM failure) becomes active and forces the CPU to enter an interrupt handler, mostly writing something like this on the screen: PARITY ERROR AT 0AB5:00BE SYSTEM HALTED. On some motherboards you can disable parity checking with standard memory. Enabled to be sure data from memory are correct. Disable only if you have 8-bit RAM, which some vendors use because it is 10% cheaper. Also, this setting is no longer necessary on recent computers since the quality and reliance of memory chips has greatly been improved.

About different memory speeds: Be sure to have memory chips of the same speed installed. It is not uncommon to have system crashes simply because memory SIMMS are of different speed. Faster memory may not adapt itself to the speed of slower memory. 60 ns and 80 ns SIMMS will surely make your system crash and yourself wonder what is the problem (I know).

  • Hard Disk Type 47 RAM Area: The BIOS has to place the HD type 47 data somewhere in memory. You can choose between DOS memory or PC BIOS (or peripheral card) memory area 0:300. DOS memory is valuable, you only have 640KB of it. So you should try to use 0:300 memory area instead. There may be some peripheral card which needs this area too (sound card, network card, whatever). So if there are some fancy cards in your PC, check the manuals if they're using the 0:300 area. But in most cases this will work without checking. This is redundant if BIOS is shadowed (maybe not in very old BIOSes). The RAM area can be verified by checking address of int41h and int46h. These are fixed disk parameters blocks. If they point to the BIOS area, BIOS made modification of parameters before mapping RAM there.
  • Wait for <F1> If Any Error: When the boot sequence encounter an error it asks you to press F1. Only at 'non-fatal' errors. If disabled, the system prints a warning and continues to boot without waiting for you to press any keys. Enabled recommended. Disabled if you want the system to operate as a server without a keyboard.
  • System Boot Up Num Lock: Specify if you want the Num Lock key to be activated at boot up. Some like it, some do not. MS-DOS (starting with 6.0, maybe earlier) allows a 'NUMLOCK=' directive in config.sys, too; if someone turns the BIOS flag off but has NUMLOCK=ON in their configuration file, they may be a bit perturbed.
  • Numeric Processor Test: Enabled if you have a math coprocessor (built in for the 486DX, 486DX2, 486DX3 and Pentium - 586 - family). Disabled if you don't (386SX, 386DX, 486SX, 486SLC and 486DLC). If disabled, your FPU (Floating Point Unit, if present) isn't recognized as present by the system and will therefore significantly decrease the performance of your system.
  • Weitek Coprocessor: If you have Weitek FPU, enable. If you have not, disable. This high performance FPU has 2-3 times the performance of the Intel FPU. Weitek uses some RAM address space, so memory from this region must be remapped somewhere else. This setting is normally found on 386 motherboards.
  • Floppy Drive Seek at Boot: Power up your A: floppy drive at boot. Disabled recommended for faster boot sequence and for reduced damage to heads. Disabling the floppy drive, changing the system boot sequence and setting a BIOS password are good techniques for adding some security to a PC.
  • System Boot Sequence: What drive the system checks first for an operating system. C:, A: recommended for faster boot sequence, or to not allow any user to enter your system by booting from the FDD if your autoexec.bat starts with a login procedure. A C: if the person who uses the computer is someone who don't knows how to setup CMOS. Because if something fails and a boot floppy won't work, many users won't know what to do next. However, be careful. You had better know this setting is turned on and be prepared to turn it off if your hard disk boot track becomes corrupted, but not obviously absent, since you otherwise won't be able to boot from floppy. Also, it's easy to fool yourself into thinking you booted from a known virus-free floppy when it actually booted from the (virus-infested) hard drive.
  • System Boot Up CPU speed: Specify at what processor speed the system will boot from. Usual settings are HIGH and LOW. HIGH recommended. If you encounter booting problems, you may try LOW. You may also change the CPU speed with Ctrl-Alt +.
  • External Cache Memory: Enabled if you have external cache memory (better known as L2 cache memory). This is a frequent error in CMOS setup as if Disabled when you have cache memory, the system performance decreases significantly. Most systems have from 64K to 512K of external cache. It is a cache between the CPU and the system bus. Different operating systems may address different levels of cache memory. For instance, DOS and Windows can address up to 64K at one time while Windows 95, OS/2 and Windows NT can address larger memory spaces. So, don't buy 256K of cache is you are using a DOS environment with less than 8MB of memory. It will not improve much the performance of your system. If Enabled when the system does not have cache memory, the system will freeze most of the time.
  • Internal Cache Memory: Enable or disable the internal cache memory of the CPU (better known as L1 cache memory). Disabled for 386 and Enabled for 486 (1 to 8KB of internal CPU cache). If the CPU does not have internal cache, the system may freeze if enabled.

In many AMI and AWARD BIOSes, the two previous options are implemented either as separate Internal and External Enable/Disable options, or as a single option (Cache Memory : Disabled/Internal/Both).

  • CPU Internal Cache: same as above.
  • Fast Gate A20 Option: Enabled recommended. A20 refers to the first 64KB of extended memory (A0 to A19) known as the 'high memory area'. This option uses the fast gate A20 line, supported in some chipsets, to access memory above 1 MB. Normally all RAM access above 1 MB is handled through the keyboard controller chip (8042 or 8742). Using this option will make the access faster than the normal method. This option is very useful in networking and multitasking operating systems.
  • Turbo Switch Function: Enables or disables the turbo switch. Disabled recommended. This setting is now removed since there are no need to switch from normal to turbo modes.
  • Shadow Memory Cacheable: You increase speed by copying ROM to RAM. Do you want to increase it by cacheing it? Yes or no - see Video BIOS Area cacheable. Yes recommended for MS-DOS and OS/2. Linux and other Unix-like operating systems will not use the cached ROMs and will benefit from the additional available memory if they are not cached.
  • Password Checking Option: Setup password to have access to the system and / or to the setup menu. Good if the computer is to be shared with several persons and you don't want anyone (friends, sister, etc.) to mess up with the BIOS. Default password: AMI (if you have AMI BIOS). Award: BIOSTAR or AWARD_SW for newer versions (Note: I even know a computer store that kept standard AWARD BIOS configuration with their systems because they didn't know what the default password was!).
  • Video ROM Shadow C000, 32K: Memory hidden under the 'I/O hole' from 0x0A0000 to 0x0FFFFF may be used to 'shadow' ROM (Read-Only Memory). Doing so, the contents of the ROM are copied into the RAM and the RAM is used instead, which is obviously faster. Video BIOS is stored in slow EPROM (Erasable Programmable Read-Only Memory) chips (120 to 150ns of access time). Also, ROM is 8 or 16 bit while RAM 32 bit wide access. With Shadow on, the EPROM content is copied to RAM (60 to 80ns of access time with 32 bit wide access). Therefore performance increases significantly. Only sensible on EGA/VGA systems. Enabled recommended. If you have flash BIOS (EEPROM), you can disable it. Flash BIOS enables access at speeds similar to memory access so you can use the memory elsewhere. However, flash BIOS is still only accessing it at the speed of the bus (ISA, EISA or VLB). On systems where the BIOS automatically steals 384K of RAM anyway, it shouldn't hurt to enable shadowing even on flash ROM. One side effect is that you will not be able to modify the contents of flash ROM when the chip is shadowed. If you reconfigure an adapter which you think might have flash ROM, and your changes are ignored, or of course if it gives you an error message when you try to change them, you'll need to temporarily disable shadowing that adapter. On (S)VGA you should enable both video shadows. Some video cards maybe using different addresses than C000 and C400. If it is the case, you should use supplied utilities that will shadow the video BIOS, in which case you should disable this setting in the CMOS. Video BIOS shadowing can cause software like XFree86 (the free X Window System) to hang. They should be probably be disabled if you run any of the 386 unixes.

Some cards map BIOS or other memory not only in the usual a0000-fffff address range, but also just below the 16MB border or at other places. The BIOS (for PCI buses only?) now allows to create a hole in the address range where the card sits. The hole may be enabled by giving an address, then a size is requested in power of 2, 64k - 1MB.

  • Adaptor ROM Shadow C800,16K: Disabled. Those addresses (C800 to EC00) are for special cards, e.g. network and controllers. Enable only if you've got an adapter card with ROM in one of these areas. It is a BAD idea to use shadow RAM for memory areas that aren't really ROM, e.g. network card buffers and other memory-mapped devices. This may interfere with the card's operation. To intelligently set these options you need to know what cards use what addresses. Most secondary display cards (like MDA and Hercules) use the ROM C800 address. Since they are slow, shadowing this address would improve their performance. An advanced tip: in some setups it is possible to enable shadow RAM without write-protecting it; with a small driver (UMM) it is then possible to use this 'shadow RAM' as UMB (Upper Memory Block) space. This has speed advantages over UMB space provided by EMM386. Some BIOSes have three options per 16KB/32KB/64KB block; e.g. disable - shadow ROM - shadow RAM or disable - shadow/WP - shadow (WP = write protect) the third option is for upper memory.
  • Adaptor ROM Shadow CC00,16K: Disabled. Some hard drive adapters use that address.
  • Adaptor ROM Shadow D000,16K: Disabled. D000 is the default Address for most Network Interface Cards.
  • Adaptor ROM Shadow D400,16K: Disabled. Some special controllers for four floppy drives have a BIOS ROM at D400 D7FF.
  • Adaptor ROM Shadow D800,16K: Disabled
  • Adaptor ROM Shadow DC00,16K: Disabled
  • Adaptor ROM Shadow E000,16K: Disabled. E000 is a good 'out of the way' place to put the EMS page frame. If necessary.
  • Adaptor ROM Shadow E400,16K: Disabled
  • Adaptor ROM Shadow E800,16K: Disabled
  • Adaptor ROM Shadow EC00,16K: Disabled. SCSI controller cards with their own BIOS could be accelerated by using Shadow RAM. Some SCSI controllers do have some RAM areas too, so it depends on the brand.

Some SCSI adapters do not use I/O-Addresses. The BIOS address range contains writable addresses, which in fact are the I/O-ports. This means this address must not be shadowed and even not be cached.

  • System ROM Shadow F000, 64K: Same thing as Video shadow, but according to the system BIOS (main computer BIOS). Enabled recommended for improved performance. System BIOS shadowing and caching should be disabled to run anything but DOS (Windows).

On older BIOS versions the shadow choices are in 400(hex)-byte increments. For instance, instead of one Video ROM Shadow segment of 32K, you will have two 16K segments (C400 and C800). Same thing for Adaptor ROM Shadow segments.

  • BootSector Virus Protection: It is not exactly a virus protection. All it does is whenever your boot sector is accessed for writing, it gives a warning to the screen allowing you to disable the access or to continue. Extremely annoying if you use something like OS/2 Boot Manager that needs to write to it. It is completely useless for SCSI or ESDI (Enhanced Small Device Interface) drives as they use their own BIOS on the controller. Disabled recommended. If you want virus protection, use a TSR (Terminate and Stay Resident) virus detection (Norton, Central Point, etc). Viruscan by Macfee is also a good idea since it is a shareware.


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