The engine blocks used in F1 are quite conventional with the upper crankcase and cylinders forming a single part. Most F1 blocks are split at the crankshaft axis with the main bearing caps and dry sump being one part, although there have been some long skirted blocks too, like this
Cosworth engine.
All previous F1 engine blocks I have seen have been cast, usually in aluminum although a few have been made in cast iron or titanium, and given the complex internal geometries machining them from solid would have been difficult or impossible. All the V8 engines had linerless blocks to maximize the bore while also minimizing the length of the engine, so did most of the later V10 engines and these blocks are not possible to machine from solid unless you make them in pieces and weld them back together (like how the internal oil cooling channel in forged motorsport pistons are made).
It was probably the V10 engines which took the casting technology to its limits since these didn't have a set minimum weight for the engine. With the V8 engine having a minimum weight, heavier castings could be used. Current F1 engines have a mandatory 80 mm bore and a mandatory engine length of 480 mm. Combined with an even higher minimum weight, smaller displacement and higher cylinder pressures this could possibly have made a machined from solid engine block feasible. But I still haven't seen any evidence of machined from solid engine blocks being used in F1, on the contrary the Renault and Ferrari blocks looks cast, probably the Honda too.
Hart is as far as I know the only engine that have had a monobloc in F1 during the modern era.
These days it's also possible to make casting molds using 3D printers.
