The Worst CPUs Ever Made

Intel Pentium 4 (Prescott) Prescott doubled down on the P4's already-long pipeline, extending it to nearly 40 stages, while Intel simultaneously shrank the P4 to a 90nm die. This was a mistake. The new chip was crippled by pipeline stalls that even its new branch prediction unit couldn't prevent and parasitic leakage drove high power consumption, preventing the chip from hitting the clocks it needed to be successful. Prescott and its dual-core sibling, Smithfield are the weakest desktop products Intel ever fielded relative to its competition at the time.

AMD Bulldozer AMD's Bulldozer was supposed to steal a march on Intel by cleverly sharing certain chip capabilities to improve efficiency and reduce die size. AMD wanted a smaller core, with higher clocks to offset any penalties related to the shared design. What it got was a disaster. Bulldozer couldn't hit its target clocks, drew too much power, and its performance was a fraction of what it needed to be. It's rare that a CPU is so bad, it nearly kills the company that invented it. Bulldozer nearly did.

Cyrix 6x86 Cyrix was one of the x86 manufacturers that didn't survive the late 1990s (VIA now holds their x86 license). Chips like the 6x86 were a major part of the reason why. Cyrix has the dubious distinction of being the reason why some games and applications carried compatibility warnings. The 6x86 was significantly faster than Intel's Pentium in integer code, but its FPU was abysmal and its chips weren't particularly stable when paired with Socket 7 motherboards. If you were a gamer in the late 1990s, you wanted an Intel CPU but could settle for AMD. The 6x86 was one of the terrible "everybody else" chips you didn't want in your Christmas stocking.

Cyrix MediaGX The MediaGX was the first attempt to build an integrated SoC processor for desktop, with graphics, CPU, PCI bus, and memory controller all on one die. Unfortunately, this happened in 1998, which means all those components were really terrible. Motherboard compatibility was incredibly limited, the underlying CPU architecture (Cyrix 5x86) was equivalent to Intel's 80486, and the CPU couldn't connect to an off-die L2 cache (the only kind of L2 cache there was, back then). Chips like the Cyrix 6x86 could at least claim to compete with Intel in business applications. The MediaGX couldn't compete with a dead manatee.

Texas Instruments TMS9900 The TMS9900 is a noteworthy failure for one enormous reason: When IBM was looking for a chip to power the original IBM PC, they had two basic choices to hit their own ship date — the TMS9900 and the Intel 8086/8088 (the Motorola 68K was under development but wasn't ready in time). The TMS9900 only had 16 bits of address space, while the 8086 had 20. That made the difference between addressing 1MB of RAM and just 64KB. TI also neglected to develop a 16-bit peripheral chip, which left the CPU stuck with performance-crippling 8-bit peripherals. The TMS9900 also had no on-chip general purpose registers; its 16 16-bit registers were all stored in main memory. TI had trouble securing partners for second-sourcing and when IBM had to pick, it picked Intel. The rest is history.

Dishonorable Mention: Qualcomm Snapdragon 810 The Snapdragon 810 was Qualcomm's first attempt to build a big.Little CPU and was based on TSMC's short-lived 20nm process. The SoC was easily Qualcomm's least-loved high-end chip in recent memory — Samsung skipped it altogether and other companies ran into serious problems with the device. QC claimed that the issues with the chip were caused by poor OEM power management, but whether the problem was related to TSMC's 20nm process, problems with Qualcomm's implementation, or OEM optimization, the result was the same: A hot-running chip that won precious few top-tier designs and is missed by no one.

Dishonorable Mention: IBM PowerPC G5 Apple's partnership with IBM on the PowerPC 970 (marketed by Apple as the G5) was supposed to be a turning point for the company. When it announced the first G5 products, Apple promised to launch a 3GHz chip within a year. But IBM failed to deliver components that could hit these clocks at reasonable power consumption and the G5 was incapable of replacing the G4 in laptops due to high power draw. Apple was forced to move to Intel and x86 in order to field competitive laptops and improve its desktop performance.

Dishonorable Mention: Pentium III 1.13GHz The P3 itself was a fine architecture. But during the race to 1GHz against AMD, Intel was desperate to maintain a performance lead, even as shipments of its high-end systems slipped further and further away (at one point, AMD was estimated to have a 12:1 advantage over Intel when it came to actually shipping 1GHz systems). In a final bid to regain the performance clock, Intel tried to push the 180nm P3 up to 1.13GHz. It failed. The chips were fundamentally unstable and Intel recalled the entire batch.

Dishonorable Mention: Cell Broadband Engine I'll take some heat for this one, but I'd toss the Cell Broadband Engine on this pile as well. Cell is an excellent example of how a chip can be phenomenally good in theory, yet nearly impossible to leverage in practice. Sony may have used it as the general processor for the PS3, but Cell was far better at multimedia and vector processing than it ever was at general purpose workloads (its design dates to a time when Sony expected to handle both CPU and GPU workloads with the same processor architecture). It's quite difficult to multi-thread the CPU to take advantage of its SPEs (Synergistic Processing Elements) and it bears little resemblance to any other architecture.