4 ms·

Since it was mentioned in the Macho Nacho video, this was quite a hurdle. But it does bring up the question, what is the theoretical maximum possible? I know th

by Cieric 2y ago

Since it was mentioned in the Macho Nacho video, this was quite a hurdle. But it does bring up the question, what is the theoretical maximum possible? I know the CPU was 32-bit, so 4GiB is the upper limit in that regard. I don't know if the CPU has limited address lanes or any other physical limitation though. The max I've seen discussed is 1.5GB for a similar cpu on a normal desktop and 640MB for the test design of the xbox (the literal pc version, not the dev kit).

toast0 2y ago
I can't figure out if the xbox processor supports PAE or not. But references say most Intel processors after pentium pro, including Pentium III support PAE. Probably with 36 bits of physical addressing. But it's a mobile socket; no idea if they put all the address pins out on those.
- wk_end 2y ago
  OT: Like you mentioned PAE was introduced with the Pentium Pro in '95. That was the same year my family got its first PC, with a whopping 8MB of RAM. It's wild to think that Intel was looking at 4GB and saying, "This probably isn't going to be enough."
  - Rinzler89 2y ago
    >It's wild to think that Intel was looking at 4GB and saying, "This probably isn't going to be enough." Not really. While consumers at home had 8MB, Intel was already looking to compete with PowerPC, DEC Alpha, MIPS systems where 4GB wasn't really out of the ordinary, so they knew where things were going.
    - LukeShu 2y ago
      As far as I know, there were only 5 PPro computers that could take >4GB: Axil Northbridge NX801, Data General AV8600, HP NetServer LXr Pro8, NCR Worldmark 4380, or Unisys XR/6 Interestingly, while the Intel 450GX chipset was designed to daisy-chain DRAM controllers (1 controller chip per 4GB of RAM), none of the boards that actually could take >4GB used that, instead building their own solutions. Presumably that meant that there was a bug in the chipset. Anyway, each of those 5 computers would have run you at least $500k in 1998. (I've been on-and-off trying to acquire one of those boxes for a few years now.)
      - trentnelson 2y ago
        Had fun googling those system names. NX801: https://www.tpc.org/results/individual_results/axil/axil.nx801.es.pdf https://www.tpc.org/results/individual_results/axil/axil.nx8... 200 9.1GB SCSI disks for 1.8TB! And still only 4GB RAM on that SQL Server 6.5 box they used for TPC-C. Wild. And yeah, $770k for that server. Edit: I guess whilst I'm at it... Data General AV8600: https://www.tpc.org/results/individual_results/dg/dg.8600.es.pdf https://www.tpc.org/results/individual_results/dg/dg.8600.es... HP NetServer LXr Pro8: https://www.1000bit.it/ad/bro/hp/netserverlxrpor8.pdf https://www.1000bit.it/ad/bro/hp/netserverlxrpor8.pdf
  - walrus01 2y ago
    at the time the original xbox was designed and its same generation of intel CPUs, the absolute practical maximum you would be able to put into a single socket desktop motherboard would be 768MB of PC100 or PC133 SDRAM (3 x 256MB DIMMs). If you actually saw a system with 768MB of RAM in it, that would be some very high-end CAD workstation. There was no practical way to get anywhere near 4GB of RAM within the dollar cost that a person purchasing a $200 CPU on a $150 motherboard would be able to bear.
  - LeFantome 2y ago
    Where I worked back in 1995, we had DEC Alpha workstations running Windows NT processing what were then huge images. We had DEC workstations running 4 GB of RAM. I think some Alpha systems had 8 GB installed even back then. The Alpha was 64 bit native but Windows NT was still 32 bit so I think you needed VMS if you wanted more than 4 GB. A 64 bit version of Windows 2000 for Alpha was created but never released ( this was the first 64 bit Windows ). It was not totally impossible to see beyond 4 GB of RAM.
- deleted 2y ago
  [deleted]
boricj 2y ago
> I know the CPU was 32-bit, so 4GiB is the upper limit in that regard. Not necessarily. Just because a CPU has a 32-bit virtual address space doesn't mean it has a 32-bit physical address space. PAE (Physical Address Extension) is a paging mode for x86 CPUs that offers a 36-bit physical address space on 32-bit CPUs.
kimixa 2y ago
As the pentium 3 used the chipset for the memory controller, it's likely limited by that, though you'll likely struggle to find specs at that sort of level publicly available. Though assuming it's the same as contemporary consumer nForce chipsets may be a good assumption [0], which may be where the 1.5gb limit discussed came from. And the p3 also supported PAE [1], so technically could address more than 4gb of ram. Though software support may be lacking - I think on the original xbox the app ran in ring0 so did things like page table management itself, rather than the "OS", so would likely require significant per-game modifications. [0] https://en.wikipedia.org/wiki/Comparison_of_Nvidia_nForce_chipsets https://en.wikipedia.org/wiki/Comparison_of_Nvidia_nForce_ch... [1] https://en.wikipedia.org/wiki/Physical_Address_Extension https://en.wikipedia.org/wiki/Physical_Address_Extension
- Cieric 2y ago
  True, I didn't know PAE was a thing till now. I figured something like that was possible, I just didn't know we had it around the time of the xbox. I guess that raises the current theoretical limit to around 64GiB? And yeah even the chip presented in the video was also noted that even 256mb wouldn't provide any benefits to games, only to homebrew or game mods and even that was overkill for anything that currently exists. Thanks for the info, I'm going to look more into it later and see if I can come up with anything more concrete.
- userbinator 2y ago
  you'll likely struggle to find specs at that sort of level publicly available Intel was far more open at that time (up through the Pentium IV era); here's the datasheet for the PIII: https://download.intel.com/design/PentiumIII/datashts/24526408.pdf https://download.intel.com/design/PentiumIII/datashts/245264... ...and yes, it does expose all 36 address bits on the FSB. The FSB protocol is actually the same as the one first used by the P6.
WhiteDawn 2y ago
In theory the chipset max is 2GB, but the physical motherboard does not have enough address lines traced to support more than 256MB. Adding more memory would require a PCB redesign
- happycube 2y ago
  ... or one crazy rework.

by Cieric 2y ago

toast0 2y ago

I can't figure out if the xbox processor supports PAE or not. But references say most Intel processors after pentium pro, including Pentium III support PAE. Probably with 36 bits of physical addressing. But it's a mobile socket; no idea if they put all the address pins out on those.

wk_end 2y ago
OT: Like you mentioned PAE was introduced with the Pentium Pro in '95. That was the same year my family got its first PC, with a whopping 8MB of RAM. It's wild to think that Intel was looking at 4GB and saying, "This probably isn't going to be enough."
- Rinzler89 2y ago
  >It's wild to think that Intel was looking at 4GB and saying, "This probably isn't going to be enough." Not really. While consumers at home had 8MB, Intel was already looking to compete with PowerPC, DEC Alpha, MIPS systems where 4GB wasn't really out of the ordinary, so they knew where things were going.
  - LukeShu 2y ago
    As far as I know, there were only 5 PPro computers that could take >4GB: Axil Northbridge NX801, Data General AV8600, HP NetServer LXr Pro8, NCR Worldmark 4380, or Unisys XR/6 Interestingly, while the Intel 450GX chipset was designed to daisy-chain DRAM controllers (1 controller chip per 4GB of RAM), none of the boards that actually could take >4GB used that, instead building their own solutions. Presumably that meant that there was a bug in the chipset. Anyway, each of those 5 computers would have run you at least $500k in 1998. (I've been on-and-off trying to acquire one of those boxes for a few years now.)
    - trentnelson 2y ago
      Had fun googling those system names. NX801: https://www.tpc.org/results/individual_results/axil/axil.nx801.es.pdf https://www.tpc.org/results/individual_results/axil/axil.nx8... 200 9.1GB SCSI disks for 1.8TB! And still only 4GB RAM on that SQL Server 6.5 box they used for TPC-C. Wild. And yeah, $770k for that server. Edit: I guess whilst I'm at it... Data General AV8600: https://www.tpc.org/results/individual_results/dg/dg.8600.es.pdf https://www.tpc.org/results/individual_results/dg/dg.8600.es... HP NetServer LXr Pro8: https://www.1000bit.it/ad/bro/hp/netserverlxrpor8.pdf https://www.1000bit.it/ad/bro/hp/netserverlxrpor8.pdf
- walrus01 2y ago
  at the time the original xbox was designed and its same generation of intel CPUs, the absolute practical maximum you would be able to put into a single socket desktop motherboard would be 768MB of PC100 or PC133 SDRAM (3 x 256MB DIMMs). If you actually saw a system with 768MB of RAM in it, that would be some very high-end CAD workstation. There was no practical way to get anywhere near 4GB of RAM within the dollar cost that a person purchasing a $200 CPU on a $150 motherboard would be able to bear.
- LeFantome 2y ago
  Where I worked back in 1995, we had DEC Alpha workstations running Windows NT processing what were then huge images. We had DEC workstations running 4 GB of RAM. I think some Alpha systems had 8 GB installed even back then. The Alpha was 64 bit native but Windows NT was still 32 bit so I think you needed VMS if you wanted more than 4 GB. A 64 bit version of Windows 2000 for Alpha was created but never released ( this was the first 64 bit Windows ). It was not totally impossible to see beyond 4 GB of RAM.
deleted 2y ago
[deleted]

boricj 2y ago

> I know the CPU was 32-bit, so 4GiB is the upper limit in that regard. Not necessarily. Just because a CPU has a 32-bit virtual address space doesn't mean it has a 32-bit physical address space. PAE (Physical Address Extension) is a paging mode for x86 CPUs that offers a 36-bit physical address space on 32-bit CPUs.

kimixa 2y ago

As the pentium 3 used the chipset for the memory controller, it's likely limited by that, though you'll likely struggle to find specs at that sort of level publicly available. Though assuming it's the same as contemporary consumer nForce chipsets may be a good assumption [0], which may be where the 1.5gb limit discussed came from. And the p3 also supported PAE [1], so technically could address more than 4gb of ram. Though software support may be lacking - I think on the original xbox the app ran in ring0 so did things like page table management itself, rather than the "OS", so would likely require significant per-game modifications. [0] https://en.wikipedia.org/wiki/Comparison_of_Nvidia_nForce_chipsets https://en.wikipedia.org/wiki/Comparison_of_Nvidia_nForce_ch... [1] https://en.wikipedia.org/wiki/Physical_Address_Extension https://en.wikipedia.org/wiki/Physical_Address_Extension

Cieric 2y ago
True, I didn't know PAE was a thing till now. I figured something like that was possible, I just didn't know we had it around the time of the xbox. I guess that raises the current theoretical limit to around 64GiB? And yeah even the chip presented in the video was also noted that even 256mb wouldn't provide any benefits to games, only to homebrew or game mods and even that was overkill for anything that currently exists. Thanks for the info, I'm going to look more into it later and see if I can come up with anything more concrete.
userbinator 2y ago
you'll likely struggle to find specs at that sort of level publicly available Intel was far more open at that time (up through the Pentium IV era); here's the datasheet for the PIII: https://download.intel.com/design/PentiumIII/datashts/24526408.pdf https://download.intel.com/design/PentiumIII/datashts/245264... ...and yes, it does expose all 36 address bits on the FSB. The FSB protocol is actually the same as the one first used by the P6.

WhiteDawn 2y ago

In theory the chipset max is 2GB, but the physical motherboard does not have enough address lines traced to support more than 256MB. Adding more memory would require a PCB redesign

happycube 2y ago
... or one crazy rework.