How Many Instructions Can a 3 GHz CPU Process Per Second

The number of instructions a 3 GHz CPU can process per second depends on several factors, including the CPU architecture, the type of instructions, and whether the CPU can execute multiple instructions per clock cycle through advanced techniques like pipelining or superscalar execution.

Base Calculation

A 3 GHz CPU has a clock speed of 3 billion cycles per second. If we assume that the CPU can execute one instruction per cycle, it would process approximately 3 billion instructions per second. This is the simplest calculation and serves as a baseline.

Advanced Execution

Many modern CPUs can execute multiple instructions per cycle. For example, if a CPU can execute 4 instructions per cycle, it could theoretically process around 12 billion instructions per second.

Therefore, while a 3 GHz CPU can process anywhere from 3 billion to potentially 12 billion or more instructions per second, the exact number depends on its architecture and capabilities.

Why It’s Complicated

While it might seem simple, it is impossible to give a correct answer to this question. Key factors that affect the number of instructions processed include:

Instructions Per Clock (IPC)

IPC is used to tell how many instructions are executed per clock. Another speed measure is MIPS (Million Instructions Per Second), but these measures can be meaningless depending on the type of instructions.

Advanced Architectural Designs

In the past, a single instruction might have taken 1 to N clock cycles. However, modern architectures, even in microcontrollers, can execute several instructions in parallel, increasing IPC above 1.

Modern CPU Architecture

Modern CPUs, including even mobile ones, deal with machine instructions or CPU binary code. Compilers convert programming languages like C, C , Java, etc., into machine binary code. The CPU then optimizes these instructions into micro-operations (uOps) and executes several in parallel.

Microcode Vulnerabilities

Intel CPUs often have vulnerabilities or bugs that are "fixed" by changing microcode. For example, the AMD Zen 3 architecture includes four ALUs (Arithmetic and Logic Units) for both integers and floating points. These ALUs enable the CPU to execute 4 integer and 4 floating point operations in parallel, achieving an IPC of 8, depending on the operations and only true for simple ones.

Specialized Benchmarks

benchmarks like Dhrystone, Whetstone, Geekbench, and Cinebench use synthetic benchmarks which do not necessarily represent real-world performance. For example, the Apple M1 has fantastic Geekbench results but different results with Cinebench, and real-world application results vary even further.

Some time ago, researchers measured the IPC of many programs in the AMD Zen architecture and concluded that the IPC was mostly around 0.8 to 1.2. This means that programs are not optimized for the architecture, whether from AMD or Intel. Workstations, however, often have programs tuned for specific architectures.

Data from Specific Benchmarks

Dhrystone for AMD/Intel

Similarly, benchmarks like Cinebench and Geekbench show different results:

Cinebench Geekbench

For example, Intel CPUs destroy every other CPU in benchmarks that utilize the AVX-512 instruction set, which is exclusive to Intel CPUs. Similarly, the Apple M1 uses its Neural Engine, leading to different benchmark results.

From the above, it is clear that different CPUs perform well in different tasks, and benchmarks can be highly task-dependent.

Another important point to note is that it is even impossible to tell how many MIPS or GIPS some CPU has, as this number varies a lot. A 3 GHz CPU could theoretically process 1 billion or 6 billion instructions per second, or even more, depending on various factors.