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On 3/28/2011 12:21, Alain wrote:
> Another problem with that, is that the CPU always have to wait for the GPU.
The Amiga (as well as some other machines of that era) and some old
mainframes would clock the memory at a multiple of the CPU speed and
time-slice the DMA that way. Now that memory is the slowest non-moving part
of the system, one can't really do that any more.
--
Darren New, San Diego CA, USA (PST)
"Coding without comments is like
driving without turn signals."
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>> requirement of 1GB for years.) What is worse, the RAM is shared by the
>> CPU
>> and the GPU, in other words, the GPU doesn't have its own RAM (as is
>> customary in a PC). This means that graphics and other game data have to
>> share the 512 MB (unlike on a PC, where graphics can be done mostly on
>> the
>> GPU's RAM and whatever the game needs on the main RAM).
It has advantages though, like not needing to transfer any data between
the CPU RAM and the GPU RAM (which is a major bottle-neck in a PC,
causing many complex algorithms to be developed). On the xbox the CPU
can update textures and meshes directly without needing to either write
a complex vertex/pixel shader or transfer over large amounts of data
per-frame.
The lack of CPU RAM isn't as large a problem as you might expect. A
well written PC game engine tries to minimise transfer between CPU RAM
and GPU RAM each frame, spreading out large data transfers (eg due to
the player entering a new part of the level) over many frames. On a
console you load the new data from disc directly to the shared RAM
rather than from CPU RAM.
Of course some things need a lot of CPU RAM which are not possible on
the xbox (or need some clever programming), but I guess they decided the
unified RAM between CPU and GPU gave the best bang-for-buck for most games.
> Another problem with that, is that the CPU always have to wait for the
> GPU. Whenever the GPU, and other display hardware, is accessing your
> RAM, NOTHING else can access it.
The difference between the xbox and normal PCs with shared memory is
that the xbox has a memory bandwidth of 22.4 GB/s. Cheap PC
motherboards today with onboard GPU have something like 8 GB/s memory
bandwidth, laptops probably lower. Even today the latest DDR3-2133 RAM
has "only" 17 GB/s.
> If it was the other way around, you'd
> get corrupted display with shearing, horizontal and vertical rolling,
> and lot of flicker.
Well you can still write to the RAM (obviously not at *exactly* the same
time as the GPU is reading it), you just make sure what you are writing
to is not needed by the GPU that frame (usually you write to a shadow
copy which then gets used the next frame).
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>> I found the graphics to be fairly tame on the PC versions of AS1 and
>> AS2.
>
> Depending on how powerful your PC is, you might be simply comparing it
> to other PC games, rather than to other Xbox 360 games.
I haven't seen any Xbox games. I'm just comparing AS1 and AS2 on the PC
to, say, Team Fortress 2 on the PC. (I could compare it to Crysis, but
surely nothing else is *that* insane...)
Don't get me wrong, the graphics weren't *bad*. They just weren't
especially great, as PC games go.
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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>>> requirement of 1GB for years.) What is worse, the RAM is shared by the
>>> CPU
>>> and the GPU, in other words, the GPU doesn't have its own RAM (as is
>>> customary in a PC). This means that graphics and other game data have to
>>> share the 512 MB (unlike on a PC, where graphics can be done mostly on
>>> the
>>> GPU's RAM and whatever the game needs on the main RAM).
>
> It has advantages though, like not needing to transfer any data between
> the CPU RAM and the GPU RAM (which is a major bottle-neck in a PC,
> causing many complex algorithms to be developed). On the xbox the CPU
> can update textures and meshes directly without needing to either write
> a complex vertex/pixel shader or transfer over large amounts of data
> per-frame.
Not at all in the case of the PCs. The GPU don't see the memory used by
the CPU, and the CPU don't see the memory used by the GPU. For the CPU,
the RAM allocated to the video just don't exist. The boundary is set on
the BIOS level and can't change at run time.
The data need to be moved between the main part of the RAM to the video
part. It passes through a simulated PCI/AGP/PCIe interface.
>
> The lack of CPU RAM isn't as large a problem as you might expect. A well
> written PC game engine tries to minimise transfer between CPU RAM and
> GPU RAM each frame, spreading out large data transfers (eg due to the
> player entering a new part of the level) over many frames. On a console
> you load the new data from disc directly to the shared RAM rather than
> from CPU RAM.
On a PC, there is NO shared RAM. On a game console, you may have it.
On a PC, the video RAM looks just like that of a dedicated video card.
>
> Of course some things need a lot of CPU RAM which are not possible on
> the xbox (or need some clever programming), but I guess they decided the
> unified RAM between CPU and GPU gave the best bang-for-buck for most games.
>
>> Another problem with that, is that the CPU always have to wait for the
>> GPU. Whenever the GPU, and other display hardware, is accessing your
>> RAM, NOTHING else can access it.
>
> The difference between the xbox and normal PCs with shared memory is
> that the xbox has a memory bandwidth of 22.4 GB/s. Cheap PC motherboards
> today with onboard GPU have something like 8 GB/s memory bandwidth,
> laptops probably lower. Even today the latest DDR3-2133 RAM has "only"
> 17 GB/s.
I'd gues that is dual ported DDR, possibly dual channel.
>
>> If it was the other way around, you'd
>> get corrupted display with shearing, horizontal and vertical rolling,
>> and lot of flicker.
>
> Well you can still write to the RAM (obviously not at *exactly* the same
> time as the GPU is reading it), you just make sure what you are writing
> to is not needed by the GPU that frame (usually you write to a shadow
> copy which then gets used the next frame).
There is an hardware, BIOS controled, mutex with absolute priority to
the GPU. There is only ONE data bus.
To do what you mention, you'd need dual ported RAM (that's totaly
different from dual channel). Dual port enable you to have 2 concurent
data exchanges, 2 reads, 2 writes, or a read and a write, at the same
time from 2 sources or destinations. Some video RAM IS dual ported and
maybe some consoles do use that kind of memory. It's not new, the Matrox
video cards used that in the 90's for consumer level dards. I have one,
a Matrox Mystic.
As warp was able to test it, a distinct video card on a PC can mean a
tenfold performance boost.
I orinaly mentioned a 50% hit, looks like it's more like an 80 to 90% hit...
Alain
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>>>> requirement of 1GB for years.) What is worse, the RAM is shared by the
>>>> CPU
>>>> and the GPU, in other words, the GPU doesn't have its own RAM (as is
>>>> customary in a PC). This means that graphics and other game data
>>>> have to
>>>> share the 512 MB
>> It has advantages though, like not needing to transfer any data between
>> the CPU RAM and the GPU RAM (which is a major bottle-neck in a PC,
>> causing many complex algorithms to be developed). On the xbox the CPU
>> can update textures and meshes directly without needing to either write
>> a complex vertex/pixel shader or transfer over large amounts of data
>> per-frame.
>
> Not at all in the case of the PCs. The GPU don't see the memory used by
> the CPU, and the CPU don't see the memory used by the GPU.
I don't know about PCs with shared memory (I can imagine they are not
designed for gaming speed!), I was talking about the xbox360, which is
specifically designed for gaming speed (with compromises that wouldn't
work for a normal PC).
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>>>>> requirement of 1GB for years.) What is worse, the RAM is shared by the
>>>>> CPU
>>>>> and the GPU, in other words, the GPU doesn't have its own RAM (as is
>>>>> customary in a PC). This means that graphics and other game data
>>>>> have to
>>>>> share the 512 MB
>
>>> It has advantages though, like not needing to transfer any data between
>>> the CPU RAM and the GPU RAM (which is a major bottle-neck in a PC,
>>> causing many complex algorithms to be developed). On the xbox the CPU
>>> can update textures and meshes directly without needing to either write
>>> a complex vertex/pixel shader or transfer over large amounts of data
>>> per-frame.
>>
>> Not at all in the case of the PCs. The GPU don't see the memory used by
>> the CPU, and the CPU don't see the memory used by the GPU.
>
> I don't know about PCs with shared memory (I can imagine they are not
> designed for gaming speed!), I was talking about the xbox360, which is
> specifically designed for gaming speed (with compromises that wouldn't
> work for a normal PC).
True.
Alain
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scott <sco### [at] scott com> wrote:
> It has advantages though, like not needing to transfer any data between
> the CPU RAM and the GPU RAM (which is a major bottle-neck in a PC,
> causing many complex algorithms to be developed). On the xbox the CPU
> can update textures and meshes directly without needing to either write
> a complex vertex/pixel shader or transfer over large amounts of data
> per-frame.
The major problem is not the speed, but the amount, as I mentioned.
The architecture would be fine, the problem is that the amount of RAM
is puny compared to modern game requirements. If the Xbox360 had, for
example, 2GB of RAM (or more), then it would really be a killer gaming
platform.
--
- Warp
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On 3/31/2011 8:58, Warp wrote:
> example, 2GB of RAM (or more), then it would really be a killer gaming
> platform.
I have noticed that games on the xbox seem to have more prettiness than the
same games on the PS3. Even looking at youtube videos of gameplay you can
tell whether it was recorded off an xbox or a ps3.
Is that just because the games I happened to look at were more polished on
the xbox, or does the xbox have actual noticably better support for
sophisticated shaders and such?
(I also noticed that the PS3 games seem to have huge wide-open spaces that I
don't see on any xbox games, but I suspect that's just my selection of
games. Altho it would make sense, having a bluray drive and probably more RAM.)
--
Darren New, San Diego CA, USA (PST)
"Coding without comments is like
driving without turn signals."
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Darren New <dne### [at] sanrrcom> wrote:
> I have noticed that games on the xbox seem to have more prettiness than the
> same games on the PS3. Even looking at youtube videos of gameplay you can
> tell whether it was recorded off an xbox or a ps3.
> Is that just because the games I happened to look at were more polished on
> the xbox, or does the xbox have actual noticably better support for
> sophisticated shaders and such?
Looking at the hardware specifications of both consoles, they seem pretty
similar: Same amount of total RAM and similar GPUs (both based on the same
generation competing GPUs of ATI and NVidia respectively). The Xbox 360 GPU
might have a slight edge in that it seems to have some 10MB specialized
internal fast framebuffer that offers 4-sample antialiasing, alpha compositing
and Z/stencil buffering practically for free.
On the PS3 the RAM is divided half-and-half between the GPU and the CPU,
with the GPU having 256 MB of dedicated RAM plus access to up to 224 MB of
the main RAM (whatever that means). I suppose that means that the CPU has
only up to 256 MB of RAM to play with (unlike the Xbox 360 where the CPU
can use all of the 512 MB). I don't know if this makes a difference, but
it might.
The CPU architectures are completely different, with the one on the PS3
being extremely exotic. The PS3 suffered a lot in its initial years because
of that (no existing game engines could be easily ported to it so that they
would take full advantage of the CPU design). In fact, AFAIK it's still
suffering from it to some extent to this day. I don't know how much of an
impact this has on game visual quality and performance.
> (I also noticed that the PS3 games seem to have huge wide-open spaces that I
> don't see on any xbox games, but I suspect that's just my selection of
> games. Altho it would make sense, having a bluray drive and probably more RAM.)
There are many Xbox 360 games that have huge sceneries, such as the
Assassin's Creed series, Red Dead Redemption, Oblivion, etc.
--
- Warp
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On 3/31/2011 10:15, Warp wrote:
> Looking at the hardware specifications of both consoles, they seem pretty
I just noticed that things on the PS3 seem less ... shiney. :-) Like,
there's much more detail in batman's cape on the xbox than the ps3, from
what I can notice without having them physically side-by-side. Maybe the
dev tools for that sort of thing are easier on the xbox, so more work goes
into making it prettier. Or it might just be my imagination. :-)
> There are many Xbox 360 games that have huge sceneries, such as the
> Assassin's Creed series, Red Dead Redemption, Oblivion, etc.
Yeah, that's the kind of thing I was thinking about. I've only personally
seen it in Uncharted and inFamous, which are PS3-specific.
Thanks for the info! :-)
--
Darren New, San Diego CA, USA (PST)
"Coding without comments is like
driving without turn signals."
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