What you're getting
The CS1W-BC033 is the 3-slot CPU backplane for the CS1 Series, mounting the power supply, CPU, and adjacent module. Bulk packaged, it carries the CS1 family with a spec line of BACKPLANE CS1 CPU 3 SLOTS.
How it sits in the CS1 panel
As a CS1 Series CPU backplane, the CS1W-BC033 mounts the CPU and power supply directly and interfaces with CS1 expansion racks downstream — it is not the I/O backplane itself. The CS1W line is the family that holds the CPU-side chassis, while the CS1 I/O racks extend off it. For a commissioning engineer this is the module the CPU is bolted to; for a wireman it sets the cabinet length budget for the CPU column; for a maintenance planner it is the spare that gets pulled first when a CS1 CPU backplane fails, because the panel will not boot without it.