What is a multi core processor?

What is a multi core processor? Why are they necessary? Multi core processors saved Intel’s bacon in 2005 when the Pentium 4 CPU failed to meet expectations, and they led to noticeable changes in the way computers are designed and marketed.

A multi core processor is a processor with multiple processor cores on a single chip. This gives improved performance, though performance doesn’t scale linearly.

The concept behind multi core processors

what is a multi core processor
When Intel found it couldn’t reach clock speeds higher than 3.8 GHz, it found it could put a pair of 2-ish GHz cores on a single chip. These multi core processors eventually ended up being better than a single 3.8 GHz processor core.

For decades, a CPU contained one processor unit per chip. This was the arrangement from the first Intel 4004 CPU in 1971 until the Pentium 4, first introduced in 2000.

The Pentium 4 was a problem for Intel. Intel initially believed the Pentium 4 would reach speeds well beyond 3.8 GHz. This turned out not to be the case, as the design ran too hot to be reliable at 4 GHz and beyond. This proved to be a problem, as the Pentium 4 wasn’t as efficient as other CPUs on the market at the time. This meant a Pentium 4 running at 1.5 GHz wasn’t as fast as a competing CPU running at the same speed. The Pentium 4’s design depended on reaching much higher speeds than the competition would be able to hit.

When Intel couldn’t get beyond 4 GHz, it had to change plans.

The dawn of multi processing

Meanwhile, high-performance computers like servers and professional workstations had been using multiple processors for improved performance for years. Multi-processor systems based on the 386 and 486 are rare, but they became much more common during the Pentium era. If you needed more performance than a 66 MHz Pentium could manage in 1993-94, you’d buy a dual-Pentium system.

There was a catch. Well, several. You had to be running Unix or Windows NT. DOS and Windows 3.1 couldn’t even see the second CPU. And software really had to be designed with multiple processors in mind to take full advantage. Excel didn’t run much faster on a system with two 66 MHz processors than it did on one with a single 66 MHz processor. You’d see a benefit if you were multitasking, because the program in the background could use the other CPU.

Multi processing remained a niche throughout the 90s and early 2000s. It was always cheaper to buy two slower CPUs than the fastest Intel CPU, but multi-processor motherboards usually erased the savings. Intel’s Celeron line changed that a bit. Intel disabled the multi-processor capability in the Celeron, but enthusiasts figured out how to re-enable it, and then Abit released a board that allowed two Celerons in a dual-CPU configuration unmodified.

Multi core processors come of age

Fortunately for Intel, when it hit the wall at 3.8 GHz, the time was right for multi processing. Windows XP had supplanted Windows 9x and ME as the mainstream operating system at the time, even for consumers, and it supported multiple processors. And Intel found it could make a single chip containing a pair of 2 GHz CPU cores much more easily than it could hit 4 GHz with a single core.

This wasn’t as good as hitting 4 GHz, but Intel could go back to a more efficient design that did more work per clock cycle and make up some of the difference. And as it worked its way back up to faster clock speeds, eventually that dual core CPU would be better than hitting 4 GHz with a single processor would be.

Intel’s first dual-core CPU, the Pentium D, was really two separate chips in a single package. Intel followed up with the Pentium M, which integrated two processor cores into a single chip. Today people don’t generally hold the Pentium D in very high regard. I’ve seen some people say the “D” stood for “disaster.” But the D and M gave Intel something better than a Pentium 4 to sell until the very successful Core 2 processor series was ready. And Intel desperately needed something better than the Pentium 4 to hold off AMD, whose original Athlon processor was also much better than the Pentium 4, and rapidly gaining market share.

Multi core processors today

Today it’s possible to buy processors with far more than two CPU cores, such as an AMD Threadripper with 32 cores. Mainstream CPUs targeting the mass market still tend to have between two and eight cores. And eventually that 4 GHz barrier fell. Today you can buy a limited number of CPUs that reach 5 GHz at least under some conditions, and the record for overclocking is over 8 GHz, though it requires special cooling to reach that speed.

But mainstream processors still tend to run in that 2-4 GHz range. The speed improvements in the last 15 years have tended to come from other means, like increasing efficiency, adding more cache, and moving more parts from separate chips on the motherboard into the CPU itself.

This means buying a CPU is more complicated than it was in the 90s, when it was clear that a 486 with a higher clock rate was faster than a lower one. And most people could grasp that a Pentium was faster than a 486 even if the Pentium had a slightly slower clock rate. Today it may not be quite as clear why an Intel i3 or AMD Ryzen 3 isn’t as fast as a more expensive i5 or Ryzen 5. Even if it is, there are a lot more CPU choices now than there were in the mid 90s. But the performance is much better now and computers last much longer, so the benefit is there, even if buying a computer hasn’t gotten any less confusing.

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