Last Updated on May 9, 2025 by Dave Farquhar
Intel’s Pentium Pro was the successor to the very successful Pentium. It was the direct ancestor of the much more successful Pentium II. But you’ll find mixed opinions of the chip. In this blog post, I will cover how the Pentium Pro could be both a failure and a triumph simultaneously.
Was the Intel Pentium Pro faster or slower than a Pentium?
When the Pentium Pro hit the market in 1996, was a bit of a disappointment. It ran at 200 MHz, which wasn’t any faster than the fastest regular Pentium at the time. That wouldn’t have necessarily been a problem. A Pentium running at 66 MHz was significantly faster than a 486 at 66 MHz. New CPUs typically get performance gains from new efficiencies as much as from higher maximum clock speeds.
The problem with the Pentium Pro was that under some circumstances, it was slower than its predecessor running at the same clock speed. It was a bit like the Pentium 4 in that regard.
The even bigger problem was the particular situation that showed the Pentium Pro’s weakness was still extremely common in 1996. If you were running 32 bit code, the Pentium Pro was faster. But if you were running 16-bit code, the Pentium was faster. And the problem in 1996 was the majority of consumers were running a mix of 16-bit and 32-bit code.
Microsoft and Intel were not in sync
The problem for Intel was the Pentium Pro was fantastic for running 32-bit operating systems. It ran Windows NT, IBM OS/2, Linux, FreeBSD, and their associated 32-bit native applications wonderfully.
But Windows 95 wasn’t a fully 32-bit operating system. It was a hybrid. And even though Microsoft had produced 32 bit native versions of their most popular software, third party software vendors frequently had not. Some of that was Microsoft’s fault. Microsoft hadn’t given third-party vendors all the documentation needed to produce native 32 bit Windows 95 apps until Office 95 was finished. This gave Microsoft a competitive advantage, but it meant anyone who used third party software was running a mix of 32-bit and 16-bit code until well into 1997.
The results was businesses who were running Windows NT and Microsoft Office 95 benefited from the Pentium Pro. But the more 16-bit legacy applications they were running under Windows NT, the more of that benefit they gave back.
And while the business market was enormous and growing rapidly in 1996, not all businesses were choosing Windows NT that year. It wouldn’t be long before Windows NT reached critical mass, but 1996 wasn’t that year. Windows NT 4.0 was the landmark release and it wasn’t available for purchase until August 1996.
On the server side, a Pentium Pro running Windows NT was competitive. I still think the DEC Alpha was faster at that point, but not a lot of Windows software was natively compiled for the Alpha. So a Pentium Pro was a better bet unless you had Alpha-compiled server software you could run on it.
The Intel Pentium Pro on the consumer side
On the consumer side of things, Windows 95 was mainstream. And hybrid 16/32-bit operating systems were the norm in the consumer space through windows me. It wasn’t until Windows XP that consumers received a consumer friendly 32-bit operating system. Yes, I knew people who ran Windows 2000 at home, but they were typically the kind of people who didn’t assume absolutely everything would run with it. They didn’t expect a parallel port scanner or a parallel port Zip drive to work with it.
All of this is to say Intel knew that the future belonged to 32-bit, but they were wrong about what year that future was going to arrive.
In Intel’s defense, when they started designing the Pentium Pro, Microsoft themselves thought the 32-bit transition would be further along by 1996. Windows 95 wasn’t supposed to be Windows 95. It was more than a year late. And Microsoft was cagey about just how much 16-bit code was in it. And the wait arrival of Windows 95 meant the 32-bit applications were also delayed.
The disappointment
It wasn’t long before magazines ran tests and told their readers that a Pentium Pro wasn’t a good buy if they intended to run Windows 95. Journalism was different back then, including tech journalism. The editors of the major PC magazines said they weren’t doing their job if some hardware manufacturer didn’t sue them once a year. Part of their job was to keep readers from getting ripped off. And they saw readers spending $600 more to get a CPU that performed worse as a ripoff.
I will also say not everyone got the memo. The IT staff at my first job was very well aware of the Pentium Pro’s strengths and limitations, so they didn’t buy a lot of them. At my second IT job, they didn’t get the memo. They bought a good number of Pentium Pro machines and they frequently ran Windows 95 on them. And I started off on the wrong foot with them when I told them they would have been better off running Windows NT on those systems. I was right, but they didn’t want to hear it from someone my age at the time.
And more than one of my coworkers in the IT department swore up and down for years that the Pentium Pro was the best CPU Intel ever made. They insisted it was more stable and more reliable than even the Pentium II.
Intel Pentium II vs Pentium Pro
Intel quickly recognized its mistake, and they tweaked the Pentium II‘s design so that it could run 16-bit code faster and they also moved the level 2 cache off the CPU die so they could ramp the clock speed higher. At 450 MHz, they didn’t have to be as efficient clock for clock as a 200 or 233 MHz Pentium MMX. As long as they were close, the higher clock speed would take care of the rest.
So that’s why some people remember the Pentium as a big success, and the Pentium II as a big success, but remember the Pentium Pro as a failure, if they remember it at all.
But that’s not to say that everyone hated it. I knew people who liked it when it was still relatively new. I think some of it was marketing. It’s easy to forget now, but Intel’s marketing in the 1990s was very effective.
It also helps to remember that for certain workloads, the Pentium Pro was better even with the less efficient 16-bit performance. Having a large CPU cache running at full speed negated some of the performance loss for certain applications. This could help explain why it had fans.
How the Pentium Pro propelled Intel to new heights
Something else we have to consider when deciding whether the Pentium Pro was a success or a failure is what it did to Intel’s placements in the broader computer market. It allowed Intel to make serious inroads into the professional workstation market, the server market, and even the supercomputer market.
ASCI Red: The Pentium Pro supercomputer
ASCI Red was the first Intel-based supercomputer, containing 9,298 Pentium Pro CPUs running in parallel. And it made a big splash.
It was the first computer to reach 1 teraflop in speed. For about three years it was the fastest supercomputer in the world. It was also one of the most reliable supercomputers ever built. The US Department of Energy operated it from 1997 to 2005.
An entire ecosystem of CPUs, computer architectures, and operating systems existed to perform work that earlier Intel CPUs weren’t well suited to perform. This was one reason why Windows NT ran on MIPS, Alpha, and Power PC in addition to x86. When Microsoft reduced the supported architectures for Windows 2000 to just Alpha and x86 during the beta testing phase and x86 exclusively upon release, it wasn’t because Microsoft was retreating from parts of the market. It was that Microsoft no longer saw those other CPU architectures as necessary.
So we have to consider the Pentium Pro for more than just how it ran Windows 95. It was the least popular x86 CPU for desktop PCs since the Intel 186. But like the 186, it had a secondary purpose, and its success beyond running Windows 95 helped make Intel what it later became.
Arguably, the Pentium Pro also helped Linux and BSD move upmarket. That’s because the combination of Linux or BSD and a Pentium Pro could reach similar performance to Unix running on a RISC CPU while providing better cost effectiveness.
David Farquhar is a computer security professional, entrepreneur, and author. He has written professionally about computers since 1991, so he was writing about retro computers when they were still new. He has been working in IT professionally since 1994 and has specialized in vulnerability management since 2013. He holds Security+ and CISSP certifications. Today he blogs five times a week, mostly about retro computers and retro gaming covering the time period from 1975 to 2000.
The Pentium Pros were first released in 166 and 180MHz speeds – and other than the change to 200MHz, the other tuning was the L2 cache size (256Kb, 512Kb, and 1Mb). I’ve always liked the Socket 8 appearance of how the pins were arranged for each half of the cache and processor areas. That design was known to have the issue of only being able to test the CPU as a whole once it was together.