5 ms·

This isn't my area but won't it be quite expensive to use that GDDR? The PHY and the controller are complicated and you've got max 2GB devices, so if you want m

by nsteel 3y ago

This isn't my area but won't it be quite expensive to use that GDDR? The PHY and the controller are complicated and you've got max 2GB devices, so if you want more memory you need a wider bus. That requires more beachfront and therefore a bigger die. That must make it expensive once you go beyond what you can fit on your small, cheap chip. Do their 24GB+ cards really use GDDR?* And you need to ensure you don't shoot yourself in the foot by making anything (relatively) cheap that could be useful for AI... *Edit: wow yeh, they do! A 384-bit interface on some! Sounds hot.

Dylan16807 3y ago
The upgrade is actually remarkably similar. RX7600 and RX7600XT have 8GB or 16GB attached to a 128-bit bus. RX7900XT and W7900 have 24GB or 48GB attached to a 384-bit bus. Neither upgrade changes the bus width, only the memory chips. The two upgraded models even use the same memory chips, as far as I can tell! GDDR6, 18000MT/s, 2GB per 16 pins. I couldn't confirm chip count on the W7900 but it's the same density.
- nsteel 3y ago
  Perhaps I should have been clearer and said "if you want more memory than the 16GB model you need a wider bus" but this confirms what I described above. - cheap gfx die with a 128-bit memory interface. - vastly more expensive gfx die with a 384-bit memory interface. Essentially there's a cheap upgrade option available for each die, swapping the 1GB memory chips for 2GB memory chips (GDDR doesn't support a mix). If you have the 16GB model and you want more memory, there are no bigger memory chips available, and so you need a wider bus and that's going to cost significantly more to produce and hence they charge more. As a side note, I would expect the the GDDR chips to be x32, rather than 16.
  - Dylan16807 3y ago
    > Essentially there's a cheap upgrade option available for each die Hmm, I think you missed what my actual point was. You can buy a card with the cheap die for $270. You can buy a card with the expensive die for $1000. So far, so good. The cost of just the memory upgrade for the cheap die is $60. The cost of just the memory upgrade for the expensive die is $3000. None of that $3000 is going toward upgrading the bus width. Maybe one percent of it goes toward upgrading the circuit board. It's a huge market segmentation fee. > As a side note, I would expect the the GDDR chips to be x32, rather than 16. The pictures I've found show the 7600 using 4 ram chips and the 7600 XT using 8 ram chips.
    - nsteel 3y ago
      I did miss your point, I misunderstood the hefty price tag was just for the memory. Thank you for not biting my head off! That is pretty mad. I'm struggling to think of any explanation other than yours. Even a few supporting upgrades maybe required for the extra memory (power supplies etc) wouldn't be anywhere near that cost. I couldn't find much to actually see how many chips used but on https://www.techpowerup.com/review/sapphire-radeon-rx-7600-xt-pulse/4.html https://www.techpowerup.com/review/sapphire-radeon-rx-7600-x... it says H56G42AS8DX-014 which is a x32 (https://product.skhynix.com/products/dram/gddr/gddr6.go?appTypCd=APX06&treeNo=1052 https://product.skhynix.com/products/dram/gddr/gddr6.go?appT...). But either way it can't explain that pricing!
      - Dylan16807 3y ago
        The first two pictures on that page show 4 RAM chips on each side of the board. https://media-www.micron.com/-/media/client/global/documents/products/technical-note/dram/tn-ed-04_gddr6_design_guide.pdf https://media-www.micron.com/-/media/client/global/documents... This document directly talks about splitting a 32 data bit connection across two GDDR6 chips, on page 7. "Allows for a doubling of density. Two 8Gb devices appear to the controller as a single, logical 16Gb device with two 16-bite wide channels." Do that with 16Gb chips and you match the GPUs we're talking about.
        nsteel 3y ago
        Of course - clamshell mode! They don't connect half the data bus from each chip. Also explains how they fit it on the card so easily without (and cheeply).
        Dylan16807 3y ago
        Yeah, though a way to connect fewer data pins to each chip doesn't particularly have to be clamshell, it just requires a little bit of flexibility in the design.

by nsteel 3y ago

Dylan16807 3y ago

The upgrade is actually remarkably similar. RX7600 and RX7600XT have 8GB or 16GB attached to a 128-bit bus. RX7900XT and W7900 have 24GB or 48GB attached to a 384-bit bus. Neither upgrade changes the bus width, only the memory chips. The two upgraded models even use the same memory chips, as far as I can tell! GDDR6, 18000MT/s, 2GB per 16 pins. I couldn't confirm chip count on the W7900 but it's the same density.

nsteel 3y ago
Perhaps I should have been clearer and said "if you want more memory than the 16GB model you need a wider bus" but this confirms what I described above. - cheap gfx die with a 128-bit memory interface. - vastly more expensive gfx die with a 384-bit memory interface. Essentially there's a cheap upgrade option available for each die, swapping the 1GB memory chips for 2GB memory chips (GDDR doesn't support a mix). If you have the 16GB model and you want more memory, there are no bigger memory chips available, and so you need a wider bus and that's going to cost significantly more to produce and hence they charge more. As a side note, I would expect the the GDDR chips to be x32, rather than 16.
- Dylan16807 3y ago
  > Essentially there's a cheap upgrade option available for each die Hmm, I think you missed what my actual point was. You can buy a card with the cheap die for $270. You can buy a card with the expensive die for $1000. So far, so good. The cost of just the memory upgrade for the cheap die is $60. The cost of just the memory upgrade for the expensive die is $3000. None of that $3000 is going toward upgrading the bus width. Maybe one percent of it goes toward upgrading the circuit board. It's a huge market segmentation fee. > As a side note, I would expect the the GDDR chips to be x32, rather than 16. The pictures I've found show the 7600 using 4 ram chips and the 7600 XT using 8 ram chips.
  - nsteel 3y ago
    I did miss your point, I misunderstood the hefty price tag was just for the memory. Thank you for not biting my head off! That is pretty mad. I'm struggling to think of any explanation other than yours. Even a few supporting upgrades maybe required for the extra memory (power supplies etc) wouldn't be anywhere near that cost. I couldn't find much to actually see how many chips used but on https://www.techpowerup.com/review/sapphire-radeon-rx-7600-xt-pulse/4.html https://www.techpowerup.com/review/sapphire-radeon-rx-7600-x... it says H56G42AS8DX-014 which is a x32 (https://product.skhynix.com/products/dram/gddr/gddr6.go?appTypCd=APX06&treeNo=1052 https://product.skhynix.com/products/dram/gddr/gddr6.go?appT...). But either way it can't explain that pricing!
    - Dylan16807 3y ago
      The first two pictures on that page show 4 RAM chips on each side of the board. https://media-www.micron.com/-/media/client/global/documents/products/technical-note/dram/tn-ed-04_gddr6_design_guide.pdf https://media-www.micron.com/-/media/client/global/documents... This document directly talks about splitting a 32 data bit connection across two GDDR6 chips, on page 7. "Allows for a doubling of density. Two 8Gb devices appear to the controller as a single, logical 16Gb device with two 16-bite wide channels." Do that with 16Gb chips and you match the GPUs we're talking about.
      - nsteel 3y ago
        Of course - clamshell mode! They don't connect half the data bus from each chip. Also explains how they fit it on the card so easily without (and cheeply).
        Dylan16807 3y ago
        Yeah, though a way to connect fewer data pins to each chip doesn't particularly have to be clamshell, it just requires a little bit of flexibility in the design.