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Windows Forum / Windows Me / General Topics / January 2007a Tech Question
Hi, I was reading up on the difference between BIOS & CMOS, and think I now how a grip on it, but I am wondering why the cmos/config program uses ram instead of rom? Wouldnt this do away with the necessity of the cmos battery? thanks for any enlightenment. Sorry, let me rephrase, I know the battery would be needed. What I meant was, why is ram the choice of memory for the cmos instead of rom? Hope this makes sense. > Hi, > [quoted text clipped - 4 lines] > > thanks for any enlightenment. > Sorry, let me rephrase, I know the battery would be needed. > What I meant was, why is ram the choice of memory for the cmos [quoted text clipped - 9 lines] >> >> thanks for any enlightenment. Hi, I'm no expert on this subject but if the memory was ROM (Read Only Memory) you wouldn't be able to make changes to the BIOS settings. You'd need a ROM burner to do that - hardly practical. That's my take on it anyway. HTH > Hi, > I'm no expert on this subject but if the memory was ROM (Read Only Memory) > you wouldn't be able to make changes to the BIOS settings. You'd need a > ROM burner to do that - hardly practical. That's my take on it anyway. > > HTH My thoughts exactly. You need to be able to adjust settings in BIOS to take account of the particular hardware connected, like what size/type of hard disks connected, what cards in which PCI slots, the date and time, amount of RAM installed etc. If it was ROM, then what was made in the factory would be all you could ever have, and no clock! Good Luck BarryG The BIOS chips (since 1990) use PROM or EPROM and not 'just plain old ROM' and are consequently able to be re-programmed (or at least partially re-programmed) by the user when adjusting (permitted) BIOS setting For a slightly more in-depth (but not too technical) explanation see the section "BIOS as firmware" at :- http://en.wikipedia.org/wiki/BIOS HTH Mart >> Hi, >> I'm no expert on this subject but if the memory was ROM (Read Only [quoted text clipped - 14 lines] > Good Luck > BarryG CMOS is used to store your computer's configuration data because it can change. If you add more memory, a new drive, a new video card, etc. CMOS would need to be updated. Since it must change it must be stored in RAM memory.  SignatureRichard G. Harper [MVP Shell/User] rgharper@gmail.com * NEW! Catch my blog ... http://msmvps.com/blogs/rgharper/ * PLEASE post all messages and replies in the newsgroups * The Website - http://rgharper.mvps.org/ * HELP us help YOU ... http://www.dts-l.org/goodpost.htm > Hi, > [quoted text clipped - 4 lines] > > thanks for any enlightenment. Thanks to all repliers. I still have a couple of things that are bugging me, will post back when I can word my concern correctly. > Hi, > [quoted text clipped - 4 lines] > > thanks for any enlightenment. "shep" <shep@heard.com> wrote in news:#58NBrkMHHA.4384 @TK2MSFTNGP03.phx.gbl: > Thanks to all repliers. > [quoted text clipped - 9 lines] >> >> thanks for any enlightenment. This scheme was developed at a time when nonvoltaile memory was either: EEPROM - handy but expensive at the time UV eraseable EPROM - expensive, and requires UV light to erase. PROM of various types - handy for the BIOS, but not reprogrammable RAM with battery backup - relatively inexpensive others - expensive or required too much room or carried too much overhead A battery was required anyway to keep the calendar/clock running, so RAM with battery backup made good economic sense. Nowadays, the RAM, calendar/clock and other items are integrated together in one chip. Putting flash memory into the chip would drive up the cost. Putting external serial flash memory external to the chip would be handy but would also drive up the cost a little. [Personally, I would prefer to have these parameters in flash so that they are not lost in the case of a battery failure, but cost seems to have pushed the vendors in the other direction.] SignatureIan Shef 805/F6 * These are my personal opinions Raytheon Company * and not those of my employer. PO Box 11337 * Tucson, AZ 85734-1337 * Interesting (personal) insight Ian - thanks for your follow-up which makes sound technical (but not seemingly, commercial <g>) sense. Mart > "shep" <shep@heard.com> wrote in news:#58NBrkMHHA.4384 > @TK2MSFTNGP03.phx.gbl: [quoted text clipped - 31 lines] > are not lost in the case of a battery failure, but cost seems to have > pushed the vendors in the other direction.] and again.... thanks to all, has been interesting, will copy and keep posts for reference. (if you dont ask, you dont get) > Interesting (personal) insight Ian - thanks for your follow-up which makes > sound technical (but not seemingly, commercial <g>) sense. [quoted text clipped - 42 lines] > > PO Box 11337 * > > Tucson, AZ 85734-1337 * So, bottom line is.... The Rom(bios) has within itself some Ram (called cmos) of which is able to be fiddled with by the user..... yeah? > Interesting (personal) insight Ian - thanks for your follow-up which makes > sound technical (but not seemingly, commercial <g>) sense. [quoted text clipped - 42 lines] > > PO Box 11337 * > > Tucson, AZ 85734-1337 * > So, bottom line is.... > The Rom(bios) has within itself some Ram (called cmos) of which is able to > be fiddled with by the user..... yeah? Conceptually, yes. In reality, no. The BIOS is software that is stored in nonvolatile memory (nowadays, Flash memory). It is executed by the CPU, which has access to various pieces of hardware. One of these pieces of hardware acts as an interface to some CMOS RAM (with battery backup). The hardware piece that acts as an interface to the CMOS RAM often also contains the real time calendar/clock that must keep running (by battery backup) when the PC is off. A user can use the Setup feature of the BIOS to "fiddle with" the CMOS RAM (because the Setup feature is really just a program running on the CPU). If permitted by the OS, the user can even access the hardware to more directly "fiddle with" the CMOS RAM, but this is dangerous. Why did I say dangerous? Losing settings is one obvious danger of fiddling with the settings. Other dangers include (on some machines) setting CPU voltages or clock speeds too high and causing permanent damage. SignatureIan Shef 805/F6 * These are my personal opinions Raytheon Company * and not those of my employer. PO Box 11337 * Tucson, AZ 85734-1337 * |
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