To add a bit more info -

P8255 and P8255A are Intel parts
INS8255 is National Semiconductor part. Note that National (as well as Fairchild) often dual marked their parts.
The INS8255 is similar to the P8255 but the INS8255 was a bit slower in a few aspects.

P8255 versus P8255A-5:
A = Die Revision, "A" is backwards compatible to the non "A" parts.
Dash number = speed grade. No dash number = 2.5MHz part, "-5" = 3.3MHz part. You can replace a 2.5MHz part with a 3.3MHz part.
The INS8255 was closer to a 2MHz part particularly with reads.