VME PIO Bandwidth

VME PIO Bandwidth

On a Challenge L or Onyx system, the maximum rate of PIO output is approximately 750K writes per second. The maximum rate of PIO input is approximately 250K reads per second. The corresponding data rate depends on the number of bytes transferred on each operation, as summarized in Table 4-1.

VME Bus PIO Bandwidth
Data Unit Size Read Write
D8 0.25 MB/second 0.75 MB/second
D16 0.5 MB/second 1.5 MB/second
D32 1 MB/second 3 MB/second

VME Bus PIO Bandwidth
Data Unit Size	Read	Write
D8	0.25 MB/second	0.75 MB/second
D16	0.5 MB/second	1.5 MB/second
D32	1 MB/second	3 MB/second

Note: The numbers in Table 4-1 were obtained by doing continuous reads, or continuous writes, to a device in the Challenge chassis. When reads and writes alternate, add approximately 1 microsecond for each change of direction. The use of a repeater to extend to an external card cage would add 200 nanoseconds or more to each transfer.