Random Access Memory , What is RAM

Random Access Memory

The Random Access Memory ( RAM ) is also alternately referred to as primary memory , temporary memory , short term memory or volatile memory .The RAM memory is considered to be the main system memory where the program first gets loaded.

The main memory RAM is an essential hardware component of every computer system. The RAM is also relatively much faster as compared to other secondary memory devices such as hard disk and SSD solid state drive.

The random access memory is a critical resource that is managed by the operating system . The operating system allocates the main memory required for the program execution.

In this article , you will learn what is RAM , its functions , RAM types , RAM speed and frequency , technical features , how to select the RAM and other important information related to this topic.

Random Access Memory ( RAM )

Table Of Contents

What Is Random Access Memory ?

What Is RAM ?

The Random Access Memory ( RAM ) is a type of high speed computer memory ( temporary storage ) used by the computer system to store the program instructions and the data during the program execution.

The computer processor ( CPU ) frequently needs to access the main memory RAM to read and write the data. The operating system loads the program into the main memory RAM to initiate the program execution.

Computer Memory Hierarchy , What Is RAM , Random Access Memory

The CPU ( Central Processing Unit ) fetches the data and instructions one by one from the RAM during the program execution. And therefore , the RAM speed is an important parameter for the system performance.

The main memory RAM is present in the computer system in the form of RAM modules ( also called as DIMM modules ) . The RAM modules are installed on the system motherboard .

Why Computer System Needs RAM ?

What Is The RAM Used For ?

The computer system needs high speed memory as a temporary memory for  the storage of program and the data before the CPU initiates the program execution.

The computer system memory unit consist of different types of memories ( disk memory , RAM and Cache memory ) arranged in a hierarchical order depending upon the data access speed.

The Cache Memory is the fastest memory that is placed close to the CPU to access frequently used data . whereas , the RAM is placed next to the cache between the CPU and disk memory. The RAM is relatively much faster than disk memory.

Computer Primary And Secondary Memory
Computer Memory Hierarchy

The disk memory is the slow memory and cannot match the CPU speed. And therefore , the computer use high speed random access memory as a main system memory .

Depending upon the system architecture , the computer system  use high speed memories such as cache and RAM , placed in between the CPU and the disk memory in order to optimize the system performance .

What Is The Use Of RAM ?

How Computer Memory Works ?

Types Of RAM ?

What is the difference between Static RAM And Dynamic RAM ?

The computer system memory unit includes cache memory and the main memory RAM . And therefore , these two high speed memories makes use of both the static RAM as well as dynamic RAM .

Both these two types of random access memories have different technical features. Since both these RAM are built using different electronics technology , each of these RAM is used for different application in a memory unit of a computer system.

In simple terms, the dynamic RAM is relatively slow as compared to the static RAM in terms of data access speed . But the dynamic RAM has advantage of smaller size and inexpensive .

These two advantages ( compact and inexpensive ) makes the dynamic RAM more suitable for the main memory RAM modules.  

Dynamic RAM

What Is Dynamic RAM , Random Access Memory

Static RAM

What Is Static RAM , Random Access Memory

On the other hand , the Static RAM is relatively very fast as compared to the dynamic RAM in terms of the data access speed .

But the static RAM has some limitations in terms its large size and it is far more expensive as compared to the dynamic RAM..

These two limitations ( large size and expensive ) makes the static RAM more suitable for the cache memory due to its very high data access speed.

Static RAM VS Dynamic RAM

S RAM

D RAM

Types Of Dynamic RAM ( DRAM )

The dynamic RAM ( DRAM ) is extensively used as a main memory in computers present in the form of RAM modules installed on the motherboard. There are two common types of  SDRAM available

SDRAM - Synchronous DRAM

DDR - Double Data Rate SDRAM

SDR SDRAM

Single Data Rate SDRAM

The CPU is driven by steady stream of clock pulses. For each clock pulse , the CPU executes a part of the instruction. This is also referred as CPU speed generally measured in GHz.

During the program execution , the CPU frequently performs read and write operations on the main memory RAM with the help of machine cycle. The machine cycle is the basic operation of the CPU.

RAM And CPU Machine Cycle

What Is Machine Cycle

The SDRAM stands for Synchronous Dynamic RAM. The SDRAM are also commonly referred to as SDR SDRAM . The SDR SDRAM stands for Single Data Rate SDRAM.

In order to optimize the CPU speed , the SDRAM synchronizes the memory speed with CPU clock speed.

Clock Speed And Instruction Cycle

This helps to reduce the latency because the memory controller knows the exact clock cycle when the requested data will be ready. And therefore , the SDRAM significantly improves the system performance .

However , the SDR SDRAM  can transfer data only during  the rising edge of the single clock cycle and hence it is called single data rate SDRAM.

DDR SDRAM

Double Data Rate SDRAM

The DDR SDRAM stands for Double Data Rate Synchronous Dynamic RAM. The DDR SDRAM is a further improvement over the SDR SDRAM .

As the name suggest , the DDR SDRAM technology can transfers the data at double the rate as compared to SDR SDRAM .

The DDR SDRAM  can transfer the data during both the rising edge of the clock cycle as well as the falling edge of the single clock cycle.

And therefore, the DDR SDRAM can double the data transfer rate without even increasing the clock signal frequency that is CPU Speed.

However , the SDR SDRAM  can transfer data only during  the rising edge of the single clock cycle and hence it is called single data rate SDRAM.

DDR SDRAM Types , Random Access Memory
DDR SDRAM Types , DDR1 , DDR2 , DDR3 , DDR4

The DDR SDRAM technology has evolved over a period of time and hence we have different versions of DDR SDRAM modules available in the market.

The DDR SDRAM started with DDR ( also called DDR1 ) and subsequently followed by DDR2 , DDR3 , DDR4 and the latest entrant is DDR5. Each newer version of DDR SDRAM had a substantial improvement over the predecessor.   

DDR SDRAM Standards

RAM Standard

Voltage

Frequency MHz

SDRAM

3.3 Volts

100 - 166  MHz

DDR1

2.5 To 2.6 Volts

266 - 400  MHz

DDR2

1.8 Volts

533 - 800  MHz

DDR3

1.35 To 1.5 Volts

1066 - 1866  MHz

DDR4

1.2 Volts

2136 - 3600  MHz

RAM FSB Speed

What is the RAM Speed And Frequency ?

The RAM is used by the system as a temporary storage to store the program data and instructions. The CPU frequently performs both memory read and write operations on the RAM during the program execution .

And therefore , the RAM speed matters in terms its ability to provide the required data and program instructions for the optimal CPU performance.

The CPU processing speed is affected every time the CPU waits for the data ( memory latency ) during the read and write operation.

The RAM FSB ( Front Side Bus ) speed is measured in Megahertz ( MHz ) . This information is usually mentioned on the label pasted on the RAM module.

This label also mentions the type of the memory ( DDR , DDR2, DDR3,  DDR4 ) and the frequency either in MHz or its PC code.

It is important to ensure the RAM compatibility with the motherboard chipset FSB speed while selecting the RAM module for any computer.

RAM FSB Speed

RAM Standard

RAM FSB Speed

RAM Code

DDR

100 MHz

PC - 1600

DDR

266 MHz

PC - 2100

DDR

333 MHz

PC - 2700

DDR

400 MHz

PC - 3200

DDR2

400 MHz

PC2 - 3200

DDR2

533 MHz

PC2 - 4200

DDR2

667 MHz

PC2 - 5300

DDR2

800 MHz

PC2 - 6400

DDR2

1066 MHz

PC2 - 8500

DDR3

800 MHz

PC3 - 6400

DDR3

1066 MHz

PC3 - 8500

DDR3

1333 MHz

PC3 - 10600

DDR3

1600 MHz

PC3 - 12800

DDR3

1867 MHz

PC3 - 14900

DDR4

1867 MHz

PC4 - 14900

DDR4

2133 MHz

PC4 - 17000

DDR4

2400 MHz

PC4 - 19200

DDR4

2666 MHz

PC4 - 21300

DDR4

4000 MHz

PC4 - 32000

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