The differences between DDR5 and DDR4

DDR5 RAM is coming. So if you’ve been thinking about building a new PC anytime soon, you’re going to have to make a decision. Should you wait and hold out for DDR5 or just go with DDR4? And you will have to decide because they are not backwards compatible. So in this topic , I’m going to try and give you all the information you possibly need about making the decision, including what’s the differences between DDR5 and DDR4, of course, and when you can expect DDR5 to come out. So let’s get into all the major differences between DDR5 and DDR4.

Memory Bandwidth

The first difference is memory bandwidth. This is basically how fast data can be retrieved from or put on to the memory stick. It’s kind of a big deal. Now with the maximum standard specifications, DDR4 has a maximum bandwidth of up to 3.2 gigabits per second, per pin. With DDR5, though, the maximum spec has up to 6.4 gigabits per second per pin, although at first it’ll probably be around 4.8 gigabits per second.

So it’s still a 50% increase, much better. But eventually as RAM improves, it’ll get up to 6.4, double this bandwidth. Now I mentioned the bandwidth per-pin. DDR4 and DDR5 have the same number of data pins, so that’s not going to make a difference here. However, the frequency of the memory is going to make a major difference, that’s the reason for the difference in memory bandwidth between the two.

The standard DDR4 spec has a frequency range of between 1600 megahertz and 3,200 megahertz, whereas the DDR5 spec is double that, between 3,200 megahertz and 6,400 megahertz. But the eventual maximum number will probably be even higher than that. I mean, even with DDR4, the maximum spec is just up to 3,200 megahertz. But you may see if you go on Newegg or something like that, you can see RAM up to about 5,000 megahertz right now, that’s probably down to overclocking.

So technically 3.2 gigahertz is the max standard spec for DDR4, but of course it is higher. So we’ll probably see much higher than the 6.4 per pin on DDR5. In fact, I’ve seen talk of about up to 8,400 megahertz for DDR5. But the main takeaway from all this is DDR5 will be capable of higher frequencies, and therefore higher memory bandwidth overall.

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Power Management

All right, the next difference between DDR4 and DDR5 is the power management structure. So with DDR4, all the power management of the RAM slot is going to be done on the motherboard itself. Whereas on DDR5, it’s going to have an actual chip called a PMIC, “power management integrated circuit”, on the chip itself. Each individual chip will be able to manage its own individual power.

So theoretically, this should mean that the RAM is going to be more power efficient, because for example, I guess if a individual RAM DIMM module requires more power at a certain moment, it will be able to get that power without having to increase the power to all the RAM at once, at least that is my understanding of it. And also I’m not 100% sure how this will affect overclocking RAM. You can do that right now through your BIOS on your motherboard. Not sure if you’ll won’t be able to do that or you will, we’ll have to see.

Channel Architecture

The next major difference between the two generations is the channel architecture. Now you may know that you can get dual channel RAM, quad channel RAM with different slots in the motherboard. This basically just makes it so the CPU can go out and access different pieces of data within each channel, whereas if there’s just one channel, the CPU can basically only get one piece of data at a time. It’s kind of like having multiple cores in the CPU.

You can do multiple stuff at once, as opposed to just one at a time. Now each DDR4 module has just one channel per stick, and it’s made up of 72 bits total, that’s 64 data bits, and then 8 bits for error correcting. With DDR5, however, each RAM modular stick has two channels. Each of those channels is a 40 bit bus, meaning it’s going to have 32 bits of data pins and then 8 for error correcting pins.

So effectively it’s the same amount of data pins between DDR4 and DDR5 on each stick. It’s 64 for both. However, with DDR5, you’re going to have two channels instead of just one. Now, like I said, DDR4 already does support multiple channels.

However, with DDR5, you can have two channels on each individual stick, which means if there’s two different pieces of data, one in each channel that the CPU wants to access in different parts, it can do both of those without having to wait for one or the other. So each individual RAM stick should be a lot more efficient, and I assume this means we’re going to be able to get a lot more potential channels in DDR5.

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Burst Length

Alright now the next big difference between DDR5 and 4 is the so-called burst length. This one is going to be a little bit technical, but I will try and explain it as best I can, as simply as I can, because it is pretty important. So DDR4 has a burst length of 8, whereas DDR5 has a burst length of 16. What does that mean? This did take a little bit of research on my part. I’m not a super expert on this obviously. I could be a little bit off in some parts, but this is my understanding. Hopefully it should be helpful.

So if you were to zoom all the way into the stick of RAM, you would see that the data is stored in arrays, which are just groups of rows and columns with each combination of the two having a bit. When a certain piece of data in the form of a bit needs to be retrieved from the RAM, the RAM will first activate a row, which basically prepares it to be read. After a certain row is activated or opened, then one bit from each row can be read from all the arrays simultaneously.

And then all of that data gets put into the output buffer to be sent to the CPU or whatever. However, this process of opening and activating a row is actually relatively slow. So if you’ve ever looked at RAM timings, the T_RCD is actually how long it takes to open a row. You’ve seen that number before. And if there’s a different row already open, it’s going to take even longer because that row must be closed first, and that amount of time is the T_RP.

So instead of doing this every single time you have to read one single bit, what the RAM can do is, because that row is already activated for a short amount of time, it can actually go ahead and read multiple columns within that row back to back. So if there’s more data in that row that needs to be read, it’s going to be way faster, way more efficient.

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And the maximum number of bits the RAM can read from a row while it’s open before needing to reopen it is called the “burst length”, because it takes a burst of data at once instead of just getting each bit one at a time.

So basically, while DDR5 is going to likely have very similar timings and latency numbers as DDR4, because it’s going to have a longer burst length in this case, it means that in more situations, it will be able to read more data without having to have those delays happen as frequently, meaning that overall it’s just going to be able to access faster speed.

Memory Capacity

All right. Now the final, big difference between DDR4 and 5 is the maximum capacity. This is a pretty fun one, because DDR5 has up to four times the maximum density of data as DDR4. Specifically, DDR4 has up to 16 gigabits of data per die, which is each individual little memory chip. However, RAM manufacturers can actually put multiple of these dies on each side of the RAM stick.

So this is called stacking. Typically they can put about eight of these on each side and then they can do it on both sides. This is called “dual rank”. When you multiply all these together, you get a grand total of 256 gigabits, which is 32 gigabytes as the maximum amount of RAM you’re going to be able to fit on one stick of RAM for DDR4. And that is probably consistent with what you’d see if you tried to go out and buy a big stick of RAM.

However, with DDR5, you can have up to 64 gigabits of data per die. So again, when you multiply all that out, 64 gigabits times eight on each side, times two sides, and then you convert to gigabytes, you get 128 gigabytes maximum per stick. However, keep in mind, it’s going to take time for the manufacturing process to build up to that maximum density. So at first, when DDR5 first comes out, you’re probably going to still see a maximum individual stick at about 32 gigabytes and then it’ll grow over time.

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