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During the POST, the BIOS must integrate multiple competing, changing, and even mutually exclusive standards and initiatives for the matrix of hardware and operating systems the PC is expected to support, although at most only simple memory tests and the setup screen are displayed.
When the battery fails, BIOS settings are reset to their defaults. The battery can also be used to power a real time clock (RTC) and the RTC, NVRAM and battery may be integrated into a single component. The name CMOS memory comes from the technology used to make the memory, which is easier to say than NVRAM. [3]
This is often called the CMOS battery or BIOS battery. The original IBM AT through to the PS/2 range, used a relatively large primary lithium battery, compared to later models, to retain the clock and configuration memory. [2] These early machines required the backup battery to be replaced periodically due to the relatively large power consumption.
Later computers, including most IBM-compatibles with 80286 CPUs, had a battery-backed nonvolatile BIOS memory (CMOS RAM chip) that held BIOS settings. [48] These settings, such as video-adapter type, memory size, and hard-disk parameters, could only be configured by running a configuration program from a disk, not built into the ROM.
Later the decreased cost of the CMOS technology allowed the same devices to be fabricated using it, adding the letter "C" to the device numbers (27xx(x) are n-MOS and 27Cxx(x) are CMOS). While parts of the same size from different manufacturers are compatible in read mode, different manufacturers added different and sometimes multiple ...
A diagnostic program (also known as a test mode) is an automatic computer program sequence that determines the operational status within the software, hardware, or any combination thereof in a component, a system, or a network of systems. Diagnostic programs ideally provide the user with guidance regarding any issues or problems found during ...
Lithium battery inside the real-time clock IC RTCs often have an alternate source of power, so they can continue to keep time while the primary source of power is off or unavailable. This alternate source of power is normally a lithium battery in older systems, but some newer systems use a supercapacitor , [ 4 ] [ 5 ] because they are ...
For both the 1525 and 1526, a low CMOS battery can prevent the computer from operating properly. [18] [19] Replacement when done the "right" way requires removal of the main board, as the CMOS is located on its underside. However, there is a method that involves shimming the case open and using an angled pick to remove and replace the battery ...