Text 8

CMOS Memory

 

Read and translate the text, using the dictionary:

 

CMOS is used in PCs to store information such as the amount of installed memory, disk types, boot up diagnostics and the real-time clock data. Here’s how to access it.

To most of us, the CMOS configuration screen is no stranger. We enter all sorts of useful system information into this screen, but we can’t seem to get this information from CMOS later. CMOS also contains a wonderful clock with a built-in-alarm, which we don’t get to use. It contains boot diagnostic results that we aren’t allowed to see.

CMOS stands for complementary metal-oxide semiconductor – a type of transistor logic used as memory. Unlike the standard dynamic RAM (DRAM) used for main memory in PC-compatible system, CMOS RAM is static. DRAM, which is generally composed of two NMOS (negative metal-oxide semiconductor) transistors and one capacitor for each bit of data, will lose its memory after a short time. To avoid this, the PC continually reads and rewrites your system’s memory, doing what’s called a memory refresh. CMOS RAM is a combination of two NMOS transistors and two PMOS (positive metal-oxide semiconductor) transistors connected in such a way that no capacitor is needed. CMOS will hold onto its memory identifinitely as long as it’s connected to a small power source (usually a battery). CMOS memory takes up a lot of silicon real estate, and is much more expensive than DRAM.

CMOS memory is used on IBM-compatible machines to store system information that needs to be preserved even when the computer is turned off.

CMOS memory is accessed by manipulating two I/O ports. The first port 70h – is a byte port used to set the address into CMOS memory. Port 70h is write only, so you can’t use it to read the current address in the CMOS memory. The second – port 71h – is used to read and write to the addressed data byte. If not handled correctly, memory access using ports 70h and 71h can create some messy problems.