Understanding RAM, CMOS, and BIOS Memory in Computers
Understanding Computer Memory: RAM, CMOS, and BIOS
RAM (Random Access Memory)
RAM is a type of temporary or volatile memory where a computer stores data it is currently working on. When the computer is turned off, the contents of RAM are erased, and any unsaved information is lost. It is generally used as the main memory of a computer.
Dynamic RAM (DRAM)
DRAM requires constant refreshing to retain data in its cells. Memory cells consist of a capacitor and an electronic circuit. The circuit generates two basic signals called CAS (Column Address Strobe) and RAS (Row Address Strobe) that handle the refresh or recharge of the memory cells. Read/write signals must be synchronized with the RAS and CAS signals.
Static RAM (SRAM)
SRAM cells are composed of electronic circuits consisting of transistors. Unlike DRAM, SRAM does not need refresh circuits. This makes it faster than DRAM, but it has higher power consumption and a lower level of integration. SRAM is typically used for caches.
Cache Memory
Cache memory is a special kind of high-speed memory designed to expedite the processing of memory instructions in the CPU. The CPU can obtain instructions and data stored in the cache memory much faster than instructions and data stored in main memory. For example, on a typical system board running at 100 MHz, the CPU needs 180 nanoseconds to get information from main memory, while it can get information from the cache in only 45 nanoseconds. Therefore, the more CPU instructions and data that can be obtained directly from the cache, the faster the PC will operate.
CMOS (Complementary Metal Oxide Semiconductor) Memory
CMOS memory is used for the setup or configuration of the PC. It is characterized by very low power consumption, so the configuration data is maintained by a battery, usually 3VDC. The system can operate even if the CMOS memory is empty, although this is not recommended. It is generally recommended to use memory from a single manufacturer to avoid compatibility problems. While memory errors are serious, mismanagement of the operating system may result in memory errors that are not actually generated by damaged hardware.
BIOS (Basic Input/Output System)
BIOS is a program contained in ROM, EPROM, or FLASH-ROM memory. It consists of lower-level routines that enable the PC to boot and control the keyboard, disk, floppy drive, and other computer components, allowing it to pass control to the operating system. When originally introduced in the PC, the BIOS contained all the drivers to handle the entire system and was burned into ROM. These drivers were preloaded into memory and accessed when you start your PC. All motherboards have a ROM BIOS chip containing a collection of embedded programs, with most having at least four core functions.
BIOS and CMOS Relationship
The BIOS is related to CMOS memory, which stores all the data that the user can modify in the BIOS-Setup, such as installed hard drives, number of heads, cylinders, the number and type of drives, the date, time, and other parameters necessary for the proper functioning of the PC.
CMOS Battery
The CMOS is constantly powered by a battery, so that once the PC is turned off, it will not lose all the data and parameters previously set by the user that the computer needs to operate and initiate. Today, all motherboards usually come with a 3V Lithium [CR2032] coin-cell battery, which lasts about 3 or 4 years. Remember that all motherboards have a way to erase all data in CMOS. In general, you must relocate a jumper or short one pair of legs and turn on the computer to reset the CMOS memory to “factory” settings.