CISC vs RISC | 1.2a | OCR A-Level Computer Science
CSNewbs
https://www.youtube.com/watch?v=17dmQATMfeI

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0:03 An instruction set is the complete collection of instructions that a CPU can execute as part of a fetch to code execute cycle. There are two main types
0:10 of instruction set architectures. Complex instruction set computer which is CISK or reduce instruction set computer which I'm going to call risk.
0:19 CISK processes use a large and complex instruction set. Each instruction can perform multiple low-level operations allowing tasks to be completed in as few
0:27 lines of code as possible. Risk processors use a smaller and simpler instruction set. Each instruction is designed to execute in a single clock
0:35 cycle, but more instructions may be needed to complete a task. CISK processes often require multiple clock cycles to execute a single complex
0:44 instruction because each instruction can perform several operations all at once, such as loading from memory, performing a calculation, and storing the result.
0:52 Risk processes are designed so that each simple instruction can be executed in a single clock cycle which allows them to achieve a steady and predictable
1:00 instruction throughput. CISK processes are more expensive to manufacture because they require more circuitry and a greater number of transistors. Risk
1:08 processors are cheaper to manufacture because they use simpler circuitry and fewer transistors to support the smaller instruction set. The extra circuitry in
1:16 a CISK processor generates more heat, so they often need cooling systems such as fans, meaning they're commonly used in desktop computers and laptops. Risk
1:24 processors are designed to use less power and produce less heat, allowing them to run without dedicated cooling systems, making them ideal for portable
1:31 devices like tablets and smartphones. Programs written for CIS processors are usually shorter, so they need less memory space to store instructions.
1:39 Programs written for risk processes tend to be longer. So they require more space in memory to store the additional instructions. CISK processes are less
1:48 efficient of pipelining because the complex instructions take varying amounts of time to execute. However, risk processes are well suited to
1:55 pipelining because their simpler instructions all take a similar amount of time to execute. And finally, some more obscure differences just so we've
2:02 officially covered every accepted difference between CISK and risk from all previous exam papers. Firstly, some instructions in CISK will rarely get
2:10 used as they're only needed in specific situations. Whereas in risks, the instruction set is smaller, so all instructions are used regularly.
2:18 Secondly, CISK instructions often include many ways to access memory, such as immediate, direct, indirect, and indexed. Modes of memory addressing is
2:26 its own topic in 2.4D, so those terms will be explained there. And risk keeps addressing mode simple, usually limited to a few types. Finally, because Risk
2:35 uses more instructions to perform a task, the compiler will be more complex. Compilers and the stages of compilation will be looked at in 2.2D and 2.2E.