Metal_Spirit
Regular
NOTE: Post corrected changing some parts as doubts are cleared.
Can someone help me with a doubt, please?
I'm going to place the thing as I see it, you guys fell free to correct me, if anything wrong.
Although the use of the word pool is not appropriate, I will use it regardless since it helps a lot in typing.
Xbox séries X as 4 1 GB modules, and 6 2 GB modules. That's 10 modules.
Each module is connected via a 2x16 bits channel, A total of 5 64 bits controllers.
The 4 1 GB modules have the 2x16 bits channels dedicated. They belong to the 10 GB fast RAM pool, and the 4 of them have a channel total of 128 bits, suplying up to 224 GB/s.
But the remaining 6 2 GB modules, they divide their capacity. The first 1 GB adds to the remaining 4 GB and constitute the 10 GB fast Pool. These 6 chips have eah a 2x16 bits channel, com we have a total os 293 biits. Add these withthe 128 bits from the 4 1 GB modules, and we have the 10 GB 320 bits pool, with 560 GB/s bandwidth.
Now, the second upper 1 GB from these 2 GB modules, constitutes de 6 GB slower pool. These do not add to anything, so we have a total of 192 bits channel, with 336 GB/s maximum bandwidth.
And so far so good!
Question is: The 2x16 bits channels we have on each of the 2 GB modules, cannot be used at the same time on both pools. If both are dedicated to the upper 1 GB on all modules we do have 336 GB on the 6 GB pool, but the 10 GB pool stops rceiving any data from these 2 GB modules, since it has no channels dedicated to it. So the fast RAM pooll decreases it's bandwidth to 244 GB/s.
Both pools till keep adding up to 560 GB/s, even though the bandwidth of each pool varies a lot.
But if we look at the upper 6 GB pool we see that we only have 3.5 GB free. The remaining memory is used by the OS.
Since the demand on this RAM will never be that big (CPU only), there is never a need to dedicate the 2x16 channels to the 6 GB slow pool.
So we can only dedicate one of these 16 bits channels, and access both pools at the same time.
In this case we have 392 GB/s on the fast ram pool, and 168 GB/s on the slow ram pool.
As I see it there are no other alternatives, unless we can acess the upper part of the 2 GB modules separately, and not on all chips at once. Is this possible?
Accepting it is not, that access to the upper part of the 2 GB requires acess to all the six at once, then 392 GB/s on the fast RAM pool, and 168 on the slow ram pool is what we can count on!
We can keep most access on the fast RAM, limiting acess to the slow RAM, but even if that increases the bandwidth available on the fast RAM, as soon as there is an acess to the slow ram (and they will need to exist), bandwidth will decrease.
This can lead to uncontrolable stutter in games. And if CPU is placed working on the slow memory, the bandwidth will vary a lot, and counting on having more than 392 GB/s on the fast memory can lead to sudden performance decreases.
But if not all of the 168 GB/s are used, the remaining is just lost, not added to the fast pool.
Now... will the GPU get 392 GB/s?
Well... no! Not even that! Off course this will depend on the game, but GPU/CPU memory usage can be 70/30 on a more demanding game. And this means, 3.5 GB will not be enough for the CPU, and he will need to use some memory on the fast pool, stealing extra bandwidth from the GPU.
Since Xbox séries X has 52 CUs, the ending result (492 GB/s) seems to be worse that the 448 GB/s available on the PS5.
Is there anything wrong with what I'm saying? I see lot of persons saying this like: "If we the CPU uses 50 GB on the slow RAM, we still have 510 GB on the fast RAM for the GPU ", but as I'm seeing it, this will not happen. As I see it 68 GB/s are wasted since those 3.5 GB will not output more that 100 GB/s, but we will need to reserve 168 GB due to the usage of the 6 16 bits channels. As such, if the CPU is working in the upper 6GB slow memory the global bandwidth will be 492 GB.
As I'm seing it, only with a very limited usage of those 6 GB, we can get more than 392 GB/s on the fast memory pool, and effectively aproaching the 560 GB/s.
Please fell free to correct me, giving your explanation.
Thank you!
Can someone help me with a doubt, please?
I'm going to place the thing as I see it, you guys fell free to correct me, if anything wrong.
Although the use of the word pool is not appropriate, I will use it regardless since it helps a lot in typing.
Xbox séries X as 4 1 GB modules, and 6 2 GB modules. That's 10 modules.
Each module is connected via a 2x16 bits channel, A total of 5 64 bits controllers.
The 4 1 GB modules have the 2x16 bits channels dedicated. They belong to the 10 GB fast RAM pool, and the 4 of them have a channel total of 128 bits, suplying up to 224 GB/s.
But the remaining 6 2 GB modules, they divide their capacity. The first 1 GB adds to the remaining 4 GB and constitute the 10 GB fast Pool. These 6 chips have eah a 2x16 bits channel, com we have a total os 293 biits. Add these withthe 128 bits from the 4 1 GB modules, and we have the 10 GB 320 bits pool, with 560 GB/s bandwidth.
Now, the second upper 1 GB from these 2 GB modules, constitutes de 6 GB slower pool. These do not add to anything, so we have a total of 192 bits channel, with 336 GB/s maximum bandwidth.
And so far so good!
Question is: The 2x16 bits channels we have on each of the 2 GB modules, cannot be used at the same time on both pools. If both are dedicated to the upper 1 GB on all modules we do have 336 GB on the 6 GB pool, but the 10 GB pool stops rceiving any data from these 2 GB modules, since it has no channels dedicated to it. So the fast RAM pooll decreases it's bandwidth to 244 GB/s.
Both pools till keep adding up to 560 GB/s, even though the bandwidth of each pool varies a lot.
But if we look at the upper 6 GB pool we see that we only have 3.5 GB free. The remaining memory is used by the OS.
Since the demand on this RAM will never be that big (CPU only), there is never a need to dedicate the 2x16 channels to the 6 GB slow pool.
So we can only dedicate one of these 16 bits channels, and access both pools at the same time.
In this case we have 392 GB/s on the fast ram pool, and 168 GB/s on the slow ram pool.
As I see it there are no other alternatives, unless we can acess the upper part of the 2 GB modules separately, and not on all chips at once. Is this possible?
Accepting it is not, that access to the upper part of the 2 GB requires acess to all the six at once, then 392 GB/s on the fast RAM pool, and 168 on the slow ram pool is what we can count on!
We can keep most access on the fast RAM, limiting acess to the slow RAM, but even if that increases the bandwidth available on the fast RAM, as soon as there is an acess to the slow ram (and they will need to exist), bandwidth will decrease.
This can lead to uncontrolable stutter in games. And if CPU is placed working on the slow memory, the bandwidth will vary a lot, and counting on having more than 392 GB/s on the fast memory can lead to sudden performance decreases.
But if not all of the 168 GB/s are used, the remaining is just lost, not added to the fast pool.
Now... will the GPU get 392 GB/s?
Well... no! Not even that! Off course this will depend on the game, but GPU/CPU memory usage can be 70/30 on a more demanding game. And this means, 3.5 GB will not be enough for the CPU, and he will need to use some memory on the fast pool, stealing extra bandwidth from the GPU.
Since Xbox séries X has 52 CUs, the ending result (492 GB/s) seems to be worse that the 448 GB/s available on the PS5.
Is there anything wrong with what I'm saying? I see lot of persons saying this like: "If we the CPU uses 50 GB on the slow RAM, we still have 510 GB on the fast RAM for the GPU ", but as I'm seeing it, this will not happen. As I see it 68 GB/s are wasted since those 3.5 GB will not output more that 100 GB/s, but we will need to reserve 168 GB due to the usage of the 6 16 bits channels. As such, if the CPU is working in the upper 6GB slow memory the global bandwidth will be 492 GB.
As I'm seing it, only with a very limited usage of those 6 GB, we can get more than 392 GB/s on the fast memory pool, and effectively aproaching the 560 GB/s.
Please fell free to correct me, giving your explanation.
Thank you!
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