AGP, vs PCI, and throw in a little UPA was Re: [SunRescue] NetBSD v. Linux v. Solaris 2.51

[James Lockwood]

On Wed, 6 Dec 2000, Christopher Byrne wrote:

> In the PCI bus, the bandwidth is shared by up to six devices. Since the bus
> itself is 32 bit, 33 mhz (for most PC implementations, and the U5/10. The
> U60, 80, and SunBlade offers at least one 64 bit 66 mhz slot) the maximum

The Sun PCI implementations also offer multiple PCI busses.  On the Ultra
5 and 10 the second 32-bit/33MHz bus is used only for onboard devices
(thus avoiding contention with expansion cards) but all other Sun PCI
based systems offer at least 2 separate busses for cards (the AXi has 2
groups of 3, for example).

> For todays 3D games that isnt that big f a deal. Most games only use 128x128
> texels anyway, and todays video cards have anywhere from 8 to 64 megs of
> very fast video RAM (DDR in some cases), but in high end 3D modeling where
> textures can be literally gigatexels in size, it can make a huge difference.

It also causes significant memory contention issues when used in this
manner with small-cache processors.  SGI worked around this with a faster
hybrid memory bus in both the O2 and Visual Workstations.

On-card texture memory is always faster when you can have enough.  The SGI
IR2 is living proof of this (expensive) memory model.  UMA models will win
when texture cache-busting occurs, or when texture data is highly dynamic.

> Suns UPA bus (Ultra Port Architecture) is very simlar in concept to AGP, but
> is even faster with UPA bus speeds into 112 mhz speed range. This allows the
> transfer of massive amounts of data through the video subsystem. Again this
> allows for the huge textures used in high end 3d applications.

The current max is 120MHz, available for 2 years:

========================= IO Cards =========================

     Bus   Freq
Brd  Type  MHz   Slot  Name                              Model
---  ----  ----  ----  --------------------------------  ----------------------
 0   UPA   120    30   FFB, Double Buffered              SUNW,501-4788         

This is available on the U5/10/AXi with either the Sabre 360 CPU or the
Sapphire Red 480 (unreleased at this point I believe).

-James