The marriage between RAM memory and processors is one of those that are inseparable, without RAM any type of processor cannot function and without a processor RAM is completely useless, but to communicate they need a series of communication channels, which they are memory channels.
The other day we talked to you about the way in which a processor accesses memory to get data and instructions, while what you are reading right now is about memory channels, which are the ways in which the processor is used. connects to RAM to transmit data and vice versa.
What are memory channels?
If we simplify the definition, the memory channels are the links between the RAM and a processor , that is, it is where the data moves between the two parts to communicate.
Historically, the first memories were single channel , but this had an added problem, since during the time when the video adapter needed to access the information to generate the screen then the CPU did not have access to the RAM , and no only the video adapter but also all the peripherals.
This led to the appearance of Video RAM , the first type of dual-channel memory, in which each memory chip had two access interfaces, which means that the addressing and data pins , as well as the interfaces that are necessary for access to data in memory access are doubled .
To communicate the processor with a memory we need a symmetric physical interface on both sides , both in memory and in RAM.
Multi-channel memory-processor configurations
We have taken three different configurations so that you can understand the way in which a processor, which can be a CPU, a GPU or any other type of xPU, communicates with the RAM.
In all the examples , although we are talking about two-channel configurations, the operation is the same for configurations with interfaces with a greater number of channels.
Case 1: Multiple channels from processor, single channel from memory
The first case is the one used today for the RAM memory in the PC , where the processor has a multi-channel interface and communicates with RAM memories that have one channel each , this allows you to place two DIMM modules of memory connected to the same processor and combine their bandwidth , since access to each of the memory modules is done simultaneously from the processor.
Case 2: Multiple channels from processor and RAM
The second case is the one that occurs when a multi-channel interface communicates with another multi-channel interface , currently this is the case of GDDR6 memory that has two 16-bit memory channels, unlike other GDDR memories that came out previously, and is also the case for future DDR5 memory .
As a curiosity, HBM memories have up to 8 different channels , being able to assign one or two channels per memory chip in the HBM stack,
Case 3; Multiple processors with one channel, multi-channel RAM
The third case is when we have a memory with multiple channels connected to several processors , this is typical in SoCs that have heterogeneous configurations of different types of processor .
For example, one memory channel can be used as video RAM and the other channel as system RAM, but it is also used in homogeneous cores where all processors are symmetrical so that the greatest number of cores have access to RAM simultaneously. .