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==Speed, Bandwidth, and Latency==
==Speed, Bandwidth, and Latency==
System bandwith (theoretical maximum):
*Cell to/from 256MB XDR : 25.6 GB/s
*Cell to RSX (IOIFO): 20GB/s (practical : 15.8GB/s @ packetsize 128B)
*Cell from RSX (IOIFI) : 15GB/s (practical : 11.9GB/s @ packetsize 128B)
*RSX to/from 256MB GDDR3 : 20.8GB/s (@ 650MHz)
Because of the aforementioned layout of the communication path between the different chips, and the latency and bandwidth differences between the various components, there are different access speeds depending on the direction of the access in relation to the source and destination. The following is a chart showing the speed of reads and writes to the GDDR3 and XDR memory from the viewpoint of the Cell and RSX. Note that these are measured speeds (rather than calculated speeds) and they should be worse if RSX and GDDR3 access are involved because these figures were measured when the RSX was clocked at 550Mhz and the GDDR3 memory was clocked at 700Mhz. The shipped PS3 has the RSX clocked in at 500Mhz (front and back end, although the pixel shaders run separately inside at 550Mhz). In addition, the GDDR3 memory was also clocked lower at 650Mhz.
Because of the aforementioned layout of the communication path between the different chips, and the latency and bandwidth differences between the various components, there are different access speeds depending on the direction of the access in relation to the source and destination. The following is a chart showing the speed of reads and writes to the GDDR3 and XDR memory from the viewpoint of the Cell and RSX. Note that these are measured speeds (rather than calculated speeds) and they should be worse if RSX and GDDR3 access are involved because these figures were measured when the RSX was clocked at 550Mhz and the GDDR3 memory was clocked at 700Mhz. The shipped PS3 has the RSX clocked in at 500Mhz (front and back end, although the pixel shaders run separately inside at 550Mhz). In addition, the GDDR3 memory was also clocked lower at 650Mhz.


Line 332: Line 325:
! Processor !! 256MB XDR !! 256MB GDDR3
! Processor !! 256MB XDR !! 256MB GDDR3
|-
|-
| Cell Read || 16.8GB/s || 16MB/s (15.6MB/s @ 650MHz)
| Cell Read || 16.8GB/s || 16MB/s
|-
|-
| Cell Write || 24.9GB/s || 4GB/s
| Cell Write || 24.9GB/s || 4GB/s
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