1.1.3: RAM & ROM

RAM – Random Access Memory.

RAM is a type of primary storage and is the main place for storing instructions while a program is being run. Data must be copied to the primary storage (RAM) from the secondary storage (Hard drive) before being executed by the CPU. For example, your OS and any programs open are stored in the RAM. However, it is volatile so once it loses power, such as when you turn your computer off, it gets wiped. To store data permanently, it needs to be written to a storage drive. RAM is much faster than a hard drive which is why data is loaded to it before being executed.

How it works:

Each block or address inside memory is numbered starting from 0 and going up in fixed values. For example, a 1 GB memory chip contains approx 270,000,000 addresses. To access the data you need to know the address of where it is stored.

A capacitor and a transistor work together to make a memory cell which represents a single bit of data. The capacitor stores the binary data (1 or 0) and the transistor acts as a switch which lets the system read the capacitor or change its state.

A capacitor is like a bucket that stores electrons. To store a 1, it is filled with electrons. To store a 0 it is emptied. However, these buckets are constantly being leaked. In a matter of a few milliseconds a bucket is emptied. Therefore, for dynamic memory (DRAM) to work, the CPU or memory controller recharges all the capacitors holding a 1 thousands of times per second to stop them from all emptying.

ROM – Read Only Memory

ROM stores essential software that enables the system to run. It stores information that enables the computer to start up. It does not store the OS. It instructs the CPU how to start up the hardware. ROM is non-volatile so it is not wiped when the computer is turned off.