RAM (random access memory)

What is RAM (random access memory)?

Random access memory (RAM) is the hardware in a computing device that provides temporary storage for the operating system (OS), software programs and any other data in current use so they're quickly available to the device's processor. RAM is often referred to as a computer's main memory, as opposed to the processor cache or other memory types.

Random access memory is considered part of a computer's primary memory. It is much faster to read from and write to than secondary storage, such as hard disk drives (HDDs), solid-state drives (SSDs) or optical drives. However, RAM is volatile; it retains data only as long as the computer is on. If power is lost, so is the data. When the computer is rebooted, the OS and other files must be reloaded into RAM, usually from an HDD or SSD.

                                                                           

                      

What is RAM (random access memory)?

Random access memory (RAM) is the hardware in a computing device that provides temporary storage for the operating system (OS), software programs and any other data in current use so they're quickly available to the device's processor. RAM is often referred to as a computer's main memory, as opposed to the processor cache or other memory types.

Random access memory is considered part of a computer's primary memory. It is much faster to read from and write to than secondary storage, such as hard disk drives (HDDs), solid-state drives (SSDs) or optical drives. However, RAM is volatile; it retains data only as long as the computer is on. If power is lost, so is the data. When the computer is rebooted, the OS and other files must be reloaded into RAM, usually from an HDD or SSD.

Random Access Memory (RAM) modules photo

Random Access Memory (RAM) modules

How does RAM work?

The term random access, or direct access, as it applies to RAM is based on the facts that any storage location can be accessed directly via its memory address and that the access can be random. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to and from specific locations. Other types of storage -- such as an HDD or CD-ROM -- can also be accessed directly and randomly, but the term random access isn't used to describe them.

Originally, the term random access memory was used to distinguish regular core memory from offline memory. Offline memory typically referred to magnetic tape from which a specific piece of data could be accessed only by locating the address sequentially, starting at the beginning of the tape.

RAM is similar in concept to a set of boxes organized into columns and rows, with each box holding either a 0 or a 1 (binary). Each box has a unique address that is determined by counting across the columns and down the rows. A set of RAM boxes is called an array, and each box is known as a cell.

To find a specific cell, the RAM controller sends the column and row address down a thin electrical line etched into the chip. Each row and column in a RAM array has its own address line. Any data that's read from the array is returned on a separate data line.

RAM is physically small and stored in microchips. The microchips are gathered into memory modules, which plug into slots in a computer's motherboard. A bus, or a set of electrical paths, is used to connect the motherboard slots to the processor.

RAM is also small in terms of the amount of data it can hold. A typical laptop computer might come with 8 GB or 16 GB of RAM, while a hard disk might hold 10 TB of data. A hard drive stores data on a magnetized surface that looks like a vinyl record. Alternatively, an SSD stores data in memory chips that, unlike RAM, are non-volatile. They don't require constant power and won't lose data if the power is turned off.

Types of RAM

RAM comes in two primary forms:

Dynamic random access memory (DRAM). DRAM is typically used for a computer's main memory. As was previously noted, it needs continuous power to retain stored data. DRAM is cheaper than SRAM and offers a higher density, but it produces more heat, consumes more power and is not as fast as SRAM.

Each DRAM cell stores a positive or negative charge held in an electrical capacitor. This data must be constantly refreshed with an electronic charge every few milliseconds to compensate for leaks from the capacitor. A transistor serves as a gate, determining whether a capacitor's value can be read or written.

Static random access memory (SRAM). This type of RAM is typically used for the system's high speed cache, such as L1 or L2. Like DRAM, SRAM also needs constant power to hold on to data, but it doesn't need to be continually refreshed the way DRAM does. SRAM is more expensive than DRAM and has a lower density, but it produces less heat, consumes less power and offers better performance.

In SRAM, instead of a capacitor holding the charge, the transistor acts as a switch, with one position serving as 1 and the other position as 0. Static RAM requires several transistors to retain one bit of data compared to dynamic RAM, which needs only one transistor per bit. This is why SRAM chips are much larger and more expensive than an equivalent amount of DRAM.

Because of the differences between SRAM and DRAM, SRAM is mainly used in small amounts, most notably as cache memory inside a computer's processor.

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