UPA Bus in an Ultra 1 Creator.
The Ultra Port Architecture (UPA) bus was developed by Sun Microsystems as a high-speed connection system between the CPU and the graphics card. It provides a speed of 15,360 Mbit / second (1,920 Megabytes / second), which puts it almost at the level of PCI-Express 1.0 x8 and AGP 8x, being clearly superior to AGP 4x. It first appeared with the Sun Ultra 1 workstation in 1995.
The UPA bus uses different bandwidth depending on which component it should communicate with. So with the RAM it uses 256 bits, with the UltraSPARC CPUs it uses 128 bits (UPA128), with the 64 bit GPU (UPA64S) and with other slower buses like the PCI bus or the SBus operates at 32 bits. Its cross-over design allows independent simultaneous connections on the bus without the need to use packet switching, much like the systems used on many high-end servers and supercomputers. This design allows you to support high-definition uncompressed video streaming (HDTV, 1920 x 1080 at 24 frames per second).
Its design became scalable, which allowed it to support the 67 MHz of the initial models of the Sun Ultra 1 (1995), which the next year passed to 83 MHz (a change of 1.07 Gigabytes / second to 1.32 GB / s with the CPU), the 100 MHz of the Sun Ultra 2 (1.6 GB / s) and the 120 MHz of the Sun Ultra 60. In the latter case it is communicated at 1.92 GB / s with the CPU already 960 MB / s with the GPU. This is possible because the UPA architecture separates the address, data and control signals, which run at the maximum speed on the bus. It also supports the possibility of using two UPA graphics cards simultaneously.
The bus has a slave-only design, not allowing a device to initiate data transfers as the PCI bus or AGP does. This is so to avoid competition from different devices (hard disks, network, etc.) can reduce bus efficiency. Thus, a graphics application that requires displaying an image of 1 million pixels with a 32-bit color depth requires 180 MB / s, less than a quarter of the bandwidth of the UPA64S bus.
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