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There are numerous cast iron forms, ranging from small ones that sit atop a burner or element to larger rectangular ones. There are even electric units of cast aluminum with teflon coatings as well.
I use one of these on my stove for small runs of pancakes or latke's.
If cooking on a campfire I can use one of these (called a spider) in the coals to invert the Dutch Oven lid onto to make a griddle.
Those electric griddles like this one are nice when cooking to produce volume or for a group. Generally teflon coated aluminum.
As a kid, my grandmother had this lovely kitchen range which had a griddle accessory that would sit to the side of the four burners. There was a plug that the griddle slid into and a knob to adjust the temperature.
I loved cooking on it and was making Crep Suzettes by the time I was 9. I also persuaded grandmother to buy loafs of Texas Toast bread so I could make French Toast. (I made egg nog and thickened it...after enjoying a glass...to use as my batter) Salmon cakes soon became a standard of mine.
Just as an aside.....this range also had something called a "Deep Well". Similar to a stock pot but the burner could be lowered about 12 inches and the aluminum pot sit flush with the surface of the range. It had a cover that fit tight and was suitable for anything for soups, stews, and deep frying. I was always making donuts in it and I think Salmon croquettes were about my last project. Then one day when I came to her house she was all excited and urged me to come in as she had something to show me. A new range. I was heart broken. LOL It didn't have any of those lovely features.
It was a Frigidair Flair range.
The silver handle in the gray panel is like a drawer and when pulled out will display four elements in a stainless cook top. Lovely thing to look at and
had one element that could be set to a specified temperature. The oven had a temperature setting with a probe to stick into the meat so it could assure
the temp in the center had been reached. (to what the gauge had been set at)