The closest cousin in the meat family to pastrami is corned beef. So, you can immediately tell that pastrami and roast beef have vast differences. They come from different cuts of meat and are prepared differently. While they are both made from beef, the result of the preparation of the two is markedly different.
You can go to your grocer, get a fresh shoulder, beef brisket, or sirloin roast, and have it for dinner tonight. However, if you want pastrami, you must buy it already prepared. Otherwise, you will need to devote weeks to prepare it before you can put it on the table for dinner or throw together pastrami on rye, and here is why.
“The main difference between pastrami vs roast beef are as follows:
1. Pastrami is a preserved meat, and roast beef is not.
2. Roast beef can be taken from the cow’s shoulder, hindquarter, neck, belly, and chest area.
3. Pastrami must go through a long preparation process before it is ready to serve. Roast beef, however, can be ready in a few hours.
Let’s look at these differences in more detail!”

Read more