By definition the word "Schedule" means a plan for carrying out a process or procedure.
The ASTM (American Society of Testing & Materials) has published a number of tables defining the standard dimensions for pipe. The individual tables are referred to as SChedules thus we have a broad range of pipe schedules from Sched, 10 through sched. 300. Basically the higher the schedule number the thicker the pipe wall.
While PVC pipe is made in a number of different schedules for pressure pipe applications for DWV (Drain, waste & vent) applications within a structure we may only use PVC Schedule 40.
ASTM standards require that all PVC pipe must have the name of the manufacturer, nominal pipe size, pipe schedule, pressure rating for water at 73degF and ASTM designation printed on the pipe wall.
The ASTM designation 1785 is for pressure pipe and the ASTM designation 2665 is for DWV pipe.
All PVC schedule 40 pipe will have the dual designation ASTM 1785 & ASTM 2665
Harvel Pipe Co. PVC 1-1/2" sched.40, 330psi @73degF ASTM 1785 & ASTM 2665
PVC pipe made to Schedule standards is commonly made in White, Gray and clear.
You will also find a light weight PVC pipe in the hardware that is White, light green or sometimes blue and labelled as SDR 30 or SDR 35. SDR is the ASTM Size Dimension Ratio standard and this pipe may not be used inside a structure. It is used primarily for storm drainage, sewer & septic leachfield lines where permitted by local codes.
The best method to cut your cast iron pipe is by means of a "Cast Iron Snap Cutter". These are fairly expensive tools and not one that I would recommend a homeowner purchase, but you can rent one from a local tool rental company for about $15 or $20 a day. The snap cutter has a chain that is wrapped around the pipe at the point where you need to cut it, then a crank is turned to pull tension of the chain and you will hear a light snap as the pipe cuts. There are other methods such as a reciprocating saw or a circular saw fitted with abrasive blades but from my experience you will burn up a number of blades before completing a cut and in the end renting a snap cutter will prove to be the most time and cost effective method.
Be very careful when cutting cast iron pipe. Cast iron is very heavy and in many instances it is not well supported, especially when cutting stacks which are typically self supporting. Before making any cuts check the hangers to be sure the remaining pipe will not fall when you make your cut. When in doubt add additional strap hangers before cutting.