CMOS

CMOS functions is to store information your computer needs when it boots up, such as hard disk types, keyboard and display type, chip set, and even the time and date. If the battery that powers your CMOS RAM dies, all this information is lost, and your PC will boot with the default information that shipped with the motherboard. In most cases, it mean you’ll have no access to your hard disks until you supply CMOS with the necessary information. Without access to your hard disks, it won’t be able to boot your operating system. Today’s CMOS RAM is protected by nickel cadmium batteries, which the computer’s power supply recharges. Its and extremely good idea to keep a copy of all the information stored in CMOS, in case disaster strikes.
The CMOS memory is a 64 or 128 bytes of RAM that is part of the system clock chip or one of the chipset chips. The information stored in CMOS is required by your computer basic Input/Output System, or BIOS. BIOS is stored in a 64k by 8 bit wide ROM on the System Board. If the System BIOS was to be accessed from this ROM during normal operation the PC’s speed would be greatly reduced. This is overcome by copying the contents of the BIOS ROM into some RAM where it is accessed from 32 or 64 bits at a time, by far at a greater speed.
How has CMOS memory change over the years?
CMOS hasn’t changed much over the years based of the information given on the internet. What I did find is that speeds have increased and the noise has been reduced it changed from analog to dialog. The IBM PC only used a small portion of CMOS memory and the balance ot the 64 bytes were left undefined. Once manufacturers cloned the AT form factor it wasn’t long that other areas of the CMOS was used by various BIOS manufacturers for such user-selectable options as memory wait states, memory type, initial boot drive selection, boot-up clock speed, hard drive interface type, green options, shadow RAM options, cache options, and password protection of the CMOS contents. It still uses a small battery in case there is a power outage and still uses volatile RAM.
Has the size of the CMOS memory increased, decreased, or stayed the same?
The size of the CMOS memory has also pretty much stayed the same because there is no need to increase the size. There was never any need to store more than 512 bytes in the memory as it holds the absolute basic boot settings for the system. The typical size is still 512 bytes. It does its job which is to get the computer started and make sure everything is in place and then hands it all over to the computer OS.
CMOS runs on about a millionth of an amp of electrical current. This efficiency allows it to store configuration data for a long time, powered only from either low-voltage dry cell or lithium batteries. On newer PCs, the CMOS battery is located on the motherboard. On older systems, like the Amstrad 1512, a pair of AA batteries mounted on top of the system powered the CMOS.