DOS Hardware Drivers

A networks "physical layer" is the hardware, while the networks "data link layer" is the driver interface. Because we will communicate with devices out of our direct control, all drivers in the communications chain must conform to the same defined protocol. An analogy of a networks data link layer protocal could be the rules and regulations which operate a nations postal service (e.g., what size envelopes can be accepted, how envelopes are to be safely transported, etc.). Drivers are specific to both the phyisical layer (hardware) and the networks "network layer" (the software passing envelopes of data to the driver). A well known data link layer protocol is called "Ethernet". Just like different nations can pass letters between their differing postal services, so too can differing data link layer protocols pass data envelopes between each other (by using a physical conversion device called a "Bridge").

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The dominant data link layer routed networking technology protocol is Ethernet, with a physical layer using ThinNet wiring. Fiber Optic wiring is becoming more prevalent, while Coax (and the very rare ThickNet) wiring is obsolete. An alternative to Ethernet is the Token Ring data link layer routed protocol, although it is being actively phased out in favor of Ethernet. The ARCNET and rare FDDI data link layer routed protocols are now of historic interest only. A popular data link layer peer-to-peer Local Area networking technology protocol is the now abandoned LocalTalk, with a physical layer using either Apple Shielded Twisted Pair wiring or a PhoneNet Adapter using Unshielded Twisted Pair wiring.

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A properly formatted data envelope (not the actual name, but easier to understand) is handed to the data link layer by the "network layer", and is analogous to a letters envelope that passes through the nations postal service between you and its destination (and like the post office, the data link layer cares nothing about what payload is wrapped inside the envelope). The network layer follows its own specific protocol, which describes the particular format to use for placing the destination address on the data envelope (so thus the destination computer using the same network protocol can decipher the address as being intended for them). Two common styles of network layer protocols are "PC/TCP Packet" and "ODI". Some data link layer driver / physical layer hardware offerings understand multiple network layer addressing formats, but if not, you can insert translating "conversion shim" software between the network layer and data link layer (however for efficiency and smaller memory footprint, it is always best if the network layer and data link layer both natively use the same singular addressing protocol).