Ram memory - everything you need to know [technical information]

RAM is one of the main components of our PC along with the CPU and the motherboard, both very well explained by us in their corresponding articles. This time we will do the same with the RAM memory modules, it is not only about the GB we want, but also what speed the board supports, which are more compatible or which are the main characteristics that we should know. We will see all this in the article that follows, so let's get started!

At the end, we will leave you a guide with the most recommended RAM memories in the current scenario so as not to make the article too long.

Index of contents

What is the function of RAM in a PC?

The RAM (Random Access Memory) is the storage where all the instructions and tasks that make up the programs and which will be used by the processor are loaded. It is a random access storage because it is possible to read or write a data in any memory location that is available, in an order prefixed by the system. RAM takes information directly from main storage, hard drives, which are much slower than it, thus avoiding bottlenecks in data transfer to the CPU.

The current RAM memory is of type DRAM or Dynamic RAM because it needs a voltage signal so that the data stored in it does not go away. When we turn off the PC and there is no power, everything stored in it will be erased. These memories are the cheapest to make by storing one bit of information for each transistor and capacitor (cell).

There is another type of memory, SRAM or Static RAM that does not need refresh, since the information bit remains stored even without power. It is more expensive to manufacture and requires more space, so they are smaller, for example, the CPU cache. Another static variant is the SSD memories, although they use NAND gates, cheaper but much slower than the cache SRAMs.

Brief overview of history

We will give a very brief overview of the evolution of RAM memory until we reach the current generation of DDR or Double Data Rate.

Magnetic Core RAM Memory

It all starts around 1949, with memories that used a magnetic core to store each bit. This core was no more than a few millimeter toroid, but huge compared to integrated circuits, so they were of very little capacity. In 1969, when silicon-based semiconductors (transistors) began to be used, Intel created a 1024- byte RAM that was the first to be marketed. Starting in 1973, technology advanced and thus the capacity of the memories, making it necessary to use expansion slots for the modular installation of SIPP and later SIMM memories .

The next memories were the FPM-RAM (Fast Page Mode RAM) in 1990 and for the first Intel 486 with speeds of 66 MHz at about 60 ns. Its design consisted of being able to send a single address and in exchange receive several of these consecutive ones.

BEDO RAM

After them, EDO-RAM (Extended Data Output RAM) and BEDO-RAM (Burst Extended…) appeared. The former were capable of receiving and sending data data, thus reaching 320 MB / s being used by the Pentium MMX and AMD K6. The latter were able to access various memory locations to send data bursts (Burt) in each clock cycle to the processor, although they were never commercialized.

Thus we reached the era of SDRAM (Synchronous Dynamic RAM) memories being memories synchronized with an internal clock to read and write data. They reached 1200 MHz with the famous Rambus (RD-RAM). After them, appeared the SDR-SDRAM (Single Data Rate-SDRAM) being the predecessors of the current DDR. These memories were directly connected to the system clock so that, in each clock cycle, they were able to read and write one data at a time.

Evolution to DDR

DDR or Double Data Rate is the current technology of RAM memory, happening in 4 generations depending on its speed and encapsulation. With them, the DIMM encapsulation began to be used, having not one, but two simultaneous data operations in the same clock cycle, thus doubling performance.

DDR

The first DDR versions came to give transfer speeds from 200 MHz to 400 MHz. They used DIMM encapsulation of 182 contacts at 2.5 V. It is important to differentiate well between bus frequency and transfer frequency (I / O), since when working with two data at the same time, the transfer frequency is twice that of the bus frequency. For example: a DDR-400 has a 200 MHz bus and 400 MHz transfer.

DDR2, DDR3 and DDR4

With DDR2, the bits transferred in each operation were doubled from 2 to 4 simultaneously, so the transfer frequency also doubled. In DIMM encapsulation it had 240 contacts at 1.8V. The DDR-1200s were the fastest, with a clock frequency of 300 MHz, a bus frequency of 600 MHz, and a transfer speed of 1200 MHz.

The 3rd and 4th generation have simply been improvements over the previous one, with less voltage and higher frequency as the size of the transistors decreases. By increasing the frequency, the latency is also increased, although it has been faster memories. DDR3s maintained a DIMM of 240 pins at 1.5 V, although not compatible with DDR2, while DDR4 rose to 288 pins at 1.35V, currently reaching 4800 or 5000 MHz transfer.

In the following sections we will focus much better on DDR4, which are currently using home consumer equipment and servers.

Commonly used interface types and where to find them

We already have a good idea of ​​the RAM memories that have circulated through computers throughout history, so let's focus on the current memories and see what types of encapsulation we can find in the different equipment.

The DIMM (Dual In-Line Memory Module) type encapsulation is currently used, consisting of a double line of copper contact pins directly glued to the double-sided edge of the memory PCB.

RAM DIMM (desktop computers)

This type of encapsulation is always used on desktop-oriented motherboards. The package has 288 contacts for DDR4 and 240 for DDR3. In the central area, heeled to one side, we have a die to ensure the correct placement of the memory in the vertical slot available on the board. The operating voltages range from 1.2 V to 1.45 V at maximum frequencies.

SO-DIMM RAM (portable equipment)

This is the compact version of the previous dual contact. In the current versions of DDR4 we find 260 contacts in slots that are placed horizontally instead of vertically. For this reason, this type of slot is used above all on laptops and also on servers, with DDR4L and DDR4U memories. These memories usually work at 1.2V to improve consumption compared to desktop computers.

Board-soldered RAM memory

Directindustry

On the other hand, we have the memory chips that are directly soldered on board, a method similar to the BGA sockets of laptop processors. This method is used in especially small equipment such as HTPC or Smartphones with LPDDR4 type memories with consumptions of only 1.1 V and frequencies of 2133 MHz

This also occurs in the case of RAM, which currently uses GDDR5 and GDDR6 chips, superior in speed to DDR4 and that are directly soldered to the PCB.

Types of RAM memory and encapsulations that currently exist

Technical characteristics that we should know about RAM memory

After seeing how and where it is connected, let's see the main characteristics to take into account of RAM. All these factors will come in the technical sheet of the module that we buy and will influence its performance.

Architecture

The architecture we can say that it is the way in which the memories communicate with the different elements to which they are connected, obviously the CPU. We currently have the DDR architecture in version 4, which is capable of writing and reading four cells of information in two simultaneous operations in each clock cycle.

Having smaller transistors and capacitors makes it easier to work at lower voltages and higher speeds, with energy savings of up to 40% compared to DDR3. Bandwidth has also been improved by 50%, reaching speeds of up to 5000 MHz. In this sense we will not have doubts, the memory to buy will always be DDR4.

Capacity

This is the pint that has 1 TB of RAM

These DDR4 memories have smaller transistors inside the memory banks, and consequently, higher cell density. In the same module we will be able to have up to 32 GB currently. The greater the capacity, the more programs can be loaded into memory, having less access to the hard disk.

Both current AMD and Intel processors support a maximum of 128GB limited by the capacity of the motherboard and its slots. In fact manufacturers like G-Skill are starting to market 256GB kits connected to 8 expansion slots for the next generation server boards and enthusiastic range. In any case, 16 or 32 GB is the trend today for home computers and gaming.

Speed

When we speak of speed in current memories we must differentiate three different measures.

• Clock frequency: which will be at the refresh rate of the memory banks. Bus frequency: Currently it is four times the clock frequency, since DDR4s work with 4 bits in each clock cycle. This speed is reflected in programs like CPU-Z in "DRAM Frequency". Transfer speed: it is the effective speed reached by data and transactions, which in DDR will be double for having a double bus. This measurement gives the name to the modules, for example PC4-2400 or PC4600.

And here is an example: a PC4-3600 memory has a clock speed of 450 MHz, while its bus works at 1800 MHz resulting in a speed of 3600 MHz.

When talking about speed in the benefits of a motherboard or RAM, we always refer to the transfer speed.

Latency

Latency is the time it takes for RAM to serve a request made by the CPU. The more frequency, the more latency there will be, although the speed will always make them modules faster despite having higher latency. Values are measured in clock cycles or clocks.

Latencies are represented in the form XXX-XX. Let's see what each number means with a typical example, a 3600 MHz DDR4 with CL 17-17-17-36:

Field	Description
CAS Latency (CL)	They are the clock cycles since a column address is sent to memory and the start of the data that is stored in it. It is the time it takes to read the first memory bit of a RAM with the correct row already open.
RAS to CAS Delay (tRCD)	The number of clock cycles required since a memory row is opened and the columns within it are accessed. The time to read the first bit of a memory without an active row is CL + TRCD.
RAS Precharge Time (tRP)	The number of clock cycles required since sending a preload command and opening the next row. The time to read the first bit of a memory if a different row is open is CL + TRCD + TRP
Row Active Time (tRAS)	The number of clock cycles required between a row trigger command and the sending of the preload command. This is the time it takes to internally refresh a row, overlapping with TRCD. In SDRAM modules (Syncronous Dynamic RAM, the usual) this value is simply CL + TRCD. Otherwise, it is approximately equal to (2 * CL) + TRCD.

These registers can be touched in the BIOS, although it is not advisable to modify the factory settings because the integrity of the module and the chips will be affected. In the case of Ryzen, there is a quite useful program called RAM Calculator that tells us the best configuration depending on the module we have.

Voltage

Voltage is simply the voltage value at which the RAM module works. As with other electronic components, the higher the speed, the more voltage will be needed to reach the frequency.

A base frequency DDR4 module (2133 MHz) works at 1.2V, but if we overclock with JEDEC profiles, we will have to raise this voltage to approximately 1.35-1.36 V.

ECC and Non-ECC

These terms appear frequently in the specifications of the memory RAM and also in the motherboard. ECC (Error Correcting Code) is a system by which RAM has an extra bit of information in transfers to detect errors between data transferred from memory and processor.

The higher the speed, the more susceptible a system will be to errors, and for this there are ECC and Non-ECC memories. However, we will always use Non-ECC type ones in our home PCs, that is, without error correction. The others are intended for computers such as servers and professional environments where altered bits can be corrected without losing data in operation. Only Intel and AMD Pro series processors and server processors support ECC memory.

Data bus: Dual and Quad Channel

For this characteristic we better make an independent section, since it is a very important function in current memories and that greatly influences the performance of a memory. First of all, let's see what are the different buses that a RAM has to communicate with the CPU.

• Data bus: line through which the content of the instructions to be processed in the CPU circulates. It is 64 bit today. Address bus: the request for a data is made through a memory address. There is a specific bus to make these requests and identify where the data is stored. Control bus: specific bus used by RAM read, write, clock and reset signals.

Dual Channel or Dual Channel technology allows simultaneous access to two different memory modules. Instead of having a 64-bit data bus, it is duplicated to 128 bits so that more instructions arrive at the CPU. The memory controllers integrated in the CPU (north bridge) have this capacity as long as the modules are connected to the DIMM of the same color on the board. Otherwise they will work independently.

On boards with AMD's X399 chipset and Intel's X299, it is possible to work with up to four modules in parallel, that is, Quad Channel, generating a 256-bit bus. For this, these memories must have in their specifications this capacity.

The performance is so superior that, if we choose to have 16 GB of RAM in our PC, it is better to do it with two 8 GB modules than to have a single 16 GB module.

Overclocking and JEDEC profiles

RAM, like any other electronic component, is liable to be overclocked. This means increasing its frequency above the a priori limits established by the manufacturer itself. Although it is true that this practice is much more controlled and limited for the user than for example graphics cards or processors.

In fact, the overclocking of the RAM memory is carried out in a controlled way since its creation directly by the manufacturer through frequency profiles that we can select from the BIOS of our computer. This is called custom JEDEC profiles. JEDEC is an organization that established the basic specifications that RAM memory manufacturers must meet, both in terms of frequencies and latencies.

So at the user level what we have is a functionality implemented in the BIOS of the motherboard that allows us to select the maximum operating profile that the board and memories support. The greater the frequency of the profile, the higher the latencies and all this is stored in the profile so that when we select it, it will give us a perfect operation without the need to manually touch frequency or times. In the event that a board does not support these profiles, it will configure the basic frequency of the RAM, that is, 2133 MHz in DDR4 or 1600 MHz in DDR3.

On Intel's part we have the technology called XMP (Extreme Memory Profiles), which is the system that we have mentioned to always take the highest performance profile of the RAM that we have installed. AMD's is called DOCP, and its function is exactly the same.

Know which, how much and what type of RAM I need

After seeing the most relevant characteristics and concepts of RAM, it could be very useful to know how to identify how much RAM our supports and at what speed it can reach. In addition, it will be useful to buy to know what RAM we currently have installed on our computer.

If we have an HTPC, the task will not bear much fruit, since they are generally computers that allow little updating of the modules because they are soldered on the board. This we would have to look at in the specifications of the equipment in question or directly open it and make an eye inspection, which we do not recommend because we will lose the warranty.

In the case of laptops, there is a constant in almost all computers: we have two SO-DIMM slots that will support a maximum of 32 or 64 GB of RAM at 2666 MHz. The question will be to know if we have one or two modules installed in it. On the part of desktop computers, it will be somewhat more variable, although almost always we will have 4 DIMMs that depending on the board will support more or less speed. The key to knowing what our PC supports will be to see the specifications of the board, while knowing the characteristics of the RAM that we have installed is reduced to installing the free CPU-Z software.

Here are the articles that interest you in every detail:

Compatibility: always an important factor in RAM memory

Sometimes it becomes a real headache to find the RAM with the best compatibility for our computer. This rather happened in previous generations of processors, and more specifically in the 1st generation AMD Ryzen, which had quite a few incompatibilities.

Currently, there are still more suitable memories than others for certain CPUs, and this is due to the type of chip used. For example, if we talk about Quad Channel for Ryzen, ECC memories for Pro range processors, etc. In the case of Intel processors, they will practically eat the memory that we put on it, which is a very good thing since brands such as Corsair, HyperX, T-Force or G.Skill will ensure optimal compatibility.

In the case of the 2nd and 3rd generation AMD Ryzen we are not going to have major problems either, although it is true that the Corsair or G.Skill modules are usually the biggest bet for them, especially with the Samsung chips. Specifically, the Dominator Series of the first and the Trident range of the second. It is always good to look at the specs on the official website to know this information beforehand.

We have a complete article where we teach step by step how to identify the compatibility between all the components of a PC.

Conclusion and guide to the best RAM memory on the market

Finally we leave you with our guide to RAM memories, where we collect the most interesting models on the market for Intel and AMD with their specifications and more. If you want to buy a memory, this is the best we have so that you don't complicate your life too much.

What RAM do you use and at what speed? If you miss any important information about RAM, leave us a comment to update the article.