wildcard mask & subnet mask

[Dopamine]

Hello everyone.
Why do we use a wildcard mask Instead subnet mask?
I know that in the wildcard mask; 0 is important and in the subnet mask 1 is important. but I can't understand why we use a wildcard mask?

[Richard Burts]

It was an implementation decision made by Cisco in the very early days of developing their products. I remember a discussion (many years ago) in which the statement was made that the machine architecture made it more efficient to process the matching for access lists using the wildcard format rather than the subnet format. 

[Dopamine]

Thankful
Is wildcard mask faster than subnet mask?

[Joseph W. Doherty]

Do you understand what a "mask" is when doing boolean logic, especially using the "and" operator?

Reason I ask, it explains much about subnet masks.

[Giuseppe Larosa · Accepted solution]

Hello @Dopamine ,

just to add to what @Richard Burts and @Joseph W. Doherty have already explained.

wildcard masks are not constrained to a single transition '0' to '1' subnet masks they are.

I mean for use in IP ACLs and extended ACLs wildcard masks provide more flexibility.

a wild card mask like 0.7.0.255 can be used in an extendel ACL line  there is no single subnet mask equivalent,

For routing exchange prefix-lists have been introduced in IOS 12.0 but they do not process user traffic.

On the other hand, when configuring an ACL on an ASA we cannot use wild card masks but we can use objects and object groups !

Hope to help

Giuseppe