Interface speeds and Bit counters as defined by Proviso

Answer

Bit Counters
Proviso checks whether the 64 bit counters are supported for both octet and packet counters. If they are, Proviso will use these counters, providing for the increased size necessary to track higher speed interfaces.

You can see this in the discovery formula for interfaces, where it sets the CounterSupport variable to values such as 64:32 (supports 64 bit octet counters, but only 32 bit packet counters), 64:64 (supports 64 bit octet and packet counters) or 32:32 (only supports 32 bit octet and packet counters).

If you look at the rules, you'll see that the rule for ~Sub-Element Collect~Interfaces~Traffic In~Octet Support~High Capacity, for example, is %(CounterSupport) LIKE '64:%' - so if the interface supports 64 bit octet counters, they will be used to collect the traffic information.

Interface Speeds
The IF-MIB defined a new variable for speed. Since the existing ifSpeed variable was 32 bits, and represented interface speed in bits per second, it could only handle interfaces up to about 4.3Gbps.

The new variable, ifHighSpeed, is still only 32 bits, but it represents interface speed in Mbps - so it can handle speeds higher than any currently available. It is less precise, however - being an integer variable, it can only represent speeds that are whole Mbps.

So Proviso uses a variable called UsesHighSpeed to mark which value (ifSpeed or ifHighSpeed) should be used in utilization calculations. This is independent of 64 bit counter support - an interface could support 64 bit counters, but still use ifSpeed to report it's capacity.

You can see this in the rule for ~Sub-Element Collect~Interfaces~Traffic In~Octet Support~High Capacity Utilization, for example - the rule is %(CounterSupport) LIKE '64:%' AND %(AP_ifSpeed) != '0' AND %(UsesHighSpeed) = 'false', which will tell Proviso to use the 64 bit counters to collect octet statistics, but ifSpeed to calculate utilization.

Similarly, the rule for ~Sub-Element Collect~Interfaces~Traffic In~Octet Support~High Speed Utilization is %(CounterSupport) LIKE '64:%' AND %(UsesHighSpeed) = 'true', which tells Proviso to use 64 bit counters and ifHighSpeed.