Exactly what does "clear CMOS" do?

"what needs to be done after the CMOS is cleared? "

Depends on how the cmos is cleared and what model of PC it is, usually nothing needs to be done, sometimes you need to enter the bios and "load defaults" (maintenance section) if it has that option.

If you have added hardware to your PC and you have also made some custom changes to your bios settings to accommodate this hardware, these will need to be changed again after a bios reset.

CMOS = Complementary metal–oxide–semiconductor

CMOS is actually a chip which the bios firmware code resides on, so you are actually resetting the bios firmware settings when you clear the CMOS. "Clear" CMOS is actually an improper term, "reset" is more accurate.

http://en.wikipedia.org/wiki/BIOS

If for some reason the bios firmware is corrupted or completely cleared from the CMOS, the PC is rendered inoperable and on a Dell, you have to replace the motherboard to correct it. This usually happens during a Failed Bios "flash".

http://www.dellcommunity.com/supportforums/search?ticket=CVrPkBwhjUA3_5687135&submitted=true&q=failed+bios+flash

The best advice is   "if it ain't broke don't fix it"

Welcome to DCF.

Thanks ty_ger & mombodog,

What I'd like to achieve is to wipe any info stored in the CMOS regarding a dodgy USB to RS232 adapter I installed. I've now gotten rid of that and installed a PCI serial port card. I suspect that the USB to RS232 adapter left some rubbish in the CMOS which is still causing problems (see my post Inspiron 530 Desktop won't boot with USB devices attached). I'll give the "clear" or "reset" a try and see if it solves my problem.

Thanks again.

"still causing problems (see my post Inspiron 530 Desktop won't boot with USB devices attached)"

I just post this in another thread and it may apply to your difficulty.

Try going into BIOS  set Boot Sequence  to HDD first and continue past to USB controllers. Expand this view and you will see three choices Off, On, and No Boot. Choose No Boot then save and exit. This may correct your difficulty.

Ratz

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Dell Precision 380 WorkStation,Tower, Pentium4 630 3GHz Prescott-2M 800, XP Pro SP2
BIOS Dell A08, MOBO Dell 0G9322 Intel Glenwood i955X Chipset
3GB, 667MHz, DDR2 SDRAM, ECC, 2x1G Crucial, 2x512 Infineon
Western Digital 800JD 80GB SATA-II 7200RPM, NCQ, 8MB Non-Raid (1st drive)
Hitachi HDT722525DLA380 250GB SATA-II 7200RPM 8MB Non-Raid (2nd drive)
Western Digital WD7500AAKS-00RBA0 16MB Non-Raid (3rd drive) awesome.
PCI Express x16 256MB Nvidia Quadro FX 3400 (6.14.11.6265 - nVIDIA ForceWare 62.65)
Mitsumi 1.44MB Floppy Drive Card Reader Combo
SONY DVD RW DRU-820A Optical Drive
PHILIPS DVD+-RW DVD8801 Optical Drive
Sound Blaster Audigy 2 ZS PCI card
Broadcom NetXtreme BCM5750 Gigabit Ethernet Controller
Conexant D850 56K V92 DFVc Modem
Dell 1907FP (Digital)
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Thanks Ratz,

I have already done that. Dell sent a tech who replaced the mother board (under warranty). He tried setting the boot device sequence to HDD first, HDD second, CD third, and no others. That didn't help either. The only thing that has worked so far for me is to set the USB device speed down from High Speed to Full/Low Speed, but that reduces performance on attached USB storage devices, so it's not good enough.

I am really beginning to think there's a problem with the way Dell's BIOSes support a lot of USB devices.

I haven't had a chance yet to clear the CMOS, but before I do I'll detach all USB devices and then delete their drivers from the Windows device manager (except the keyboard and mouse), including hidden drivers. Then I'll reintroduce them one at a time and see how the boot goes after each one. One device I won't be adding back is the USB to RS232 converter I had used previously (I'll spell out the brand and model of that on this forum if it turns out to be the culprit).

KumbiaKid