Is ARM still RISC

CISC and RISC

CISC and RISC are different concepts for computers or processors. CISC stands for a processor that has an extensive set of instructions. On the other hand, RISC stands for a processor that has a reduced instruction set.

There are always discussions with the central question of whether CISC or RISC processors are superior. But there are many factors that influence the efficiency and performance of a processor. The differences between CISC and RISC only play an academic role here.
In the past, a distinction was made between CISC and RISC for processors. But today, modern processors no longer have anything in common with these old concepts. In order to be able to call a modern processor a CISC or RISC processor, one would have to analyze its interior more closely.

Classic RISC processors are mainly used in smartphones and tablets. The ARM architecture is a typical representative. Intel and AMD processors are understood as typical CISC processors that work internally with RISC-like structures.

CISC - Complex Instruction Set Computing

CISC stands for Complex Instruction Set Computing. The CISC processor is characterized by a large number of commands and complex addressing options. Although an extensive set of commands is available, only a few commands and addresses are used in practice. Because only a few parts of the processor are used, this is extremely inefficient.

Each instruction has its own microcode in the ROM memory of the CISC processor. With each command call, the decoder unit divides the command into the machine command, the type of addressing, the addresses and the registers. Then small instructions, the microcode, are sent to the nanoprocessor. This is a processor in the processor that executes the microcode in its complex circuits. The microcode is executed in sequence. All other instructions have to wait that long. To make matters worse, the internal bus slows down the entire CPU when accessing memory.
Unfortunately, this procedure is very slow because the microcode requires several work steps, which is very time-consuming. CISC processors usually require four to ten clock cycles until a command is completely executed.

Research in the 1970s showed that around 80% of all calculations in a typical application are performed with around 20% of the instructions in the processor. In addition, the same command sequences are always required for many calculations. These findings led to the development of the RISC processor.

RISC - Reduced Instruction Set Computing

RISC stands for Reduced Instruction Set Computing. Translated, this is a computer (processor) with a reduced instruction set that contains only a few elementary instructions. Most instructions can be executed within a few clock cycles. Few and simple commands result in a simpler processor structure in which there are simple digital circuits and whose commands are hard-wired (in the control unit). It relies on independent processing units, several separate internal bus systems and parallel processing of the commands.
All RISC commands have the same format and there is only one way to load or save them. Because they don't have to be decoded into smaller microcodes, RISC instructions load much faster than CISC instructions.
Practically every processor today is a RISC processor or at least has RISC elements in it.
RISC processors are essentially cheaper to manufacture, smaller and more manageable in terms of their interconnection.

Processor architectures

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Everything you need to know about computer technology.

Computer technology primer

The computer technology primer is a book about the basics of computer technology, processor technology, semiconductor memory, interfaces, data storage, drives and important hardware components.

I want that!