Yes, it would be slow and large. Because it's large, you'd get less memory in the same area. Another factor is that RAM and CPUs are usually on completely dif

Yes, it would be slow and large. Because it's large, you'd get less memory in the same area. Another factor is that RAM and CPUs are usually on completely different dies to begin with, which are manufactured with somewhat different processes so you can't just copy and paste them onto the same chip. Incidentally, this is what computers looked like 30 years ago. You could have a CPU with a bunch of address and data pins wired up to a RAM chip that would give you whatever address you wanted right away. Loosely speaking, a modern computer still works the same way, but memory speeds haven't kept up with CPU speeds. So, to make our software run faster, we put layers of smaller, faster memory between the CPU and the larger, slower memory. But the hardware hides all of this from the software: you don't have to care, unless you want to optimize things. So we have registers, L1 cache, L2 cache, RAM, SSDs, HDDs, and the network. You can write a program today and all seven layers of caching might be mostly transparent, some more so than others. A lot of this complexity is in the hardware, and other parts of it are in the OS. Application developers have it easy.