A switch's frame/packet forwarding performance, PPS (packets per second), and switching (fabric) bandwidth, bps (bits per second), both measure the capacity of a switch for moving transit traffic through it. This capacity, generally, is "shared" across all the switch's ports, regardless of whether they are a host edge port or a trunk port (or even the "speed" of the port).
Switch bandwidth supports the aggregate usage of all ports, actually transmitting traffic.
For example, if you had a two gig port switch, using full duplex ports, the ports could utilize, up to, two gigs of bandwidth (although Cisco fabric switch specs, would note this as four gigs of bandwidth, because they count both ports ingress/egress to the fabric).
PPS requirements depends on bandwidth rate and frame/packet size. For minimum sized Ethernet packets (64 bytes) (minimum often used for a performance requirement, as it's the worst case), gig bandwidth requires a PPS of 1.544 Mpps. So, again for our two gig port switch, it would need about 3 Gbps to support both gig ports running at wire-speed/line-rate, concurrently.
BTW, some switches do not provide sufficient PPS or fabric bandwidth, to support all their ports, at full "speed", concurrently.
