(to allow fast context switches). More important enhancements were the doubling of the instruction and data cache sizes and a few microarchitectural changes for better performance. The Pentium was designed to execute over 100 million instructions per second (MIPS), and the 75 MHz model was able to reach 126.5 MIPS in certain benchmarks. The Pentium architecture typically offered just under twice the performance of a 486 processor per clock cycle in common benchmarks. The fastest 80486 parts (with slightly improved microarchitecture and 100 MHz operation) were almost as powerful as the first-generation Pentiums, and the AMD Am5x86, which despite its name is actually a 486-class CPU, was roughly equal to the Pentium 75 regarding pure ALU performance. Errata The early versions of 60–100 MHz P5 Pentiums had a problem in the floating-point unit that resulted in incorrect (but predictable) results from some division operations. This flaw, discovered in 1994 by professor Thomas Nicely at Lynchburg College, Virginia, became widely known as the Pentium FDIV bug and caused embarrassment for Intel, which created an exchange program to replace the faulty processors. In 1997, another erratum was discovered that could allow a malicious program to crash a system without any special privileges, the "F00F bug". All P5 series processors were affected and no fixed steppings were ever released, however contemporary operating systems were patched with workarounds to prevent crashes. Cores and steppings The Pentium was Intel's primary microprocessor for personal computers during the mid-1990s. The original design was reimplemented in newer processes and new features were added to maintain its competitiveness, and to address specific markets such as portable computers. As a result, there were several variants of the P5 microarchitecture. P5 The first Pentium microprocessor core was code-named "P5". Its product code was 80501 (80500 for the earliest steppings Q0399). There were two versions, specified to operate at 60 MHz and 66 MHz respectively, using Socket 4. This first implementation of the Pentium used a traditional 5-volt power supply (descended from the usual transistor-transistor logic (TTL) compatibility requirements). It contained 3.1 million transistors and measured 16.7 mm by 17.6 mm for an area of 293.92 mm2. It was fabricated in a 0.8 μm bipolar complementary metal–oxide–semiconductor (BiCMOS) process. The 5-volt design resulted in relatively high energy consumption for its operating frequency when compared to the directly following models. P54C The P5 was followed by the P54C (80502) in 1994, with versions