Pentium OverDrive
Intel's upgrade processor for 486, Pentium, and Pentium Pro systems.
The Pentium OverDrive was a brand name Intel used in the mid-1990s for a range of processor upgrades. It first appeared on 486 motherboards, then later for certain Pentium sockets and Socket 8 systems.
For 486 systems, the OverDrive used a heavily modified 3.3-volt Pentium P54 core built on a 0.6-micrometer process. It included a 486-compatible bus unit (with more pins), an integrated heatsink and fan, and 32 kB of level 1 cache—double the 16 kB found on standard P54C chips. Because the data bus was reduced to 32-bit width, its per-clock performance was lower than a regular Pentium, but it was still much faster than a similarly clocked 486 due to architectural improvements like a better FPU. It also had an integrated 3.3-volt power regulator, since many 486 boards only supplied 5 volts.
The 63 MHz model launched in February 1995 and worked with 25 MHz bus systems. The faster 83 MHz version, supporting both 25 MHz (63 MHz effective) and 33 MHz bus systems, came out in September 1995 and cost $299—expensive compared to alternatives like AMD's 5x86 or Cyrix's Cx5x86 chips.
The heatsink was permanently attached, and the removable fan module got power through spring-like metal prongs connecting to three conductors on the chip's surface. The fan release clip is visible at the top left corner of the CPU in photos. A central plastic column from the fan's center houses the wiring, running down the side of the heatsink at that corner. Small plastic points at the top left of this column form the locking mechanism, released by squeezing them. The opposite corner has a latch that swings into place to lock the fan under the heatsink. The processor monitors the fan; if it stops, the chip throttles back its clock speed to prevent overheating and damage—a predecessor to modern Intel temperature detection and protection.
During development, Intel changed the design specification, causing compatibility and performance issues with some boards that had previously worked fine. For example, the Packard Bell 450 motherboard needed a special interposer between the processor and motherboard to handle the changed spec, but this blocked access to the motherboard's level 2 cache, hurting performance. Some older chipsets also didn't support the chip's write-back L1 cache, further reducing performance.
- First release
- February 1995 (63 MHz model for 486 systems)
- Manufacturing technology
- 0.6 micrometer
- Voltage
- 3.3 volts (with integrated regulator for 5V boards)
- L1 cache
- 32 kB (16 kB + 16 kB)
- Notable models
- PODP5V63 (63 MHz), PODP5V83 (83 MHz), PODP3V125 (125 MHz), PODP3V150 (150 MHz), PODP3V166 (166 MHz), PODPMT66X200 (200 MHz), PODP66X333 (300/333 MHz)
- Socket compatibility
- Socket 3 (486), Socket 4, Socket 5, Socket 8
- Asci red upgrade
- 1999, all 4,510 computing nodes upgraded to dual Pentium II OverDrive CPUs
Lore & Background
The Pentium OverDrive for 486 systems was a heavily modified, 3.3-volt Pentium P54 core manufactured on 0.6 micrometer technology. It was fitted with a 486-compatible bus unit (with an increased pin-count), an integrated heatsink and fan, and 32 kB of level 1 cache—double the 16 kB offered on regular P54C chips. As the data bus was effectively reduced to 32-bit width, per-clock performance was much lower than that of a regular Pentium, though still substantially faster compared to a similarly clocked 486 owing to architectural improvements such as the much improved FPU. It also had an integrated 3.3 volt power regulator, as many 486 motherboards only provided 5 volt power. The 63 MHz model launched in February 1995, supporting 25 MHz bus systems; the 83 MHz version, supporting both 25 and 33 MHz bus systems, launched later that year in September, priced at $299. The processor's heatsink is permanently attached, and the removable fan module is powered via spring-like metal prongs. The processor monitors the fan and will throttle back on clock speed to prevent overheating if the fan is not operating, a predecessor to internal temperature detection in later Intel processors. During development, Intel changed the design specification, causing compatibility and performance problems with some boards; for instance, the Packard Bell 450 motherboard required a specially designed interposer, precluding access to the motherboard's level 2 cache. However, the majority of Socket 3 motherboards, particularly later VLB and most PCI boards, provided proper support. For Pentium sockets, Intel released OverDrive chips for Socket 4 (5V) using an internal clock multiplier of 2, and for Socket 5 (3.3V) running at 125, 150, and 166 MHz (clock multiplier of 2.5). These were later replaced by Pentium OverDrive MMX, which upgraded Pentium 120–200 MHz systems with MMX technology. In 1998, the Pentium II OverDrive was released for Socket 8, combining the 0.25 μm Deschutes core of the Pentium II with a 512 kB full-speed L2 cache chip from the Pentium II Xeon, resulting in a processor running at 300 or 333 MHz. This upgrade could be used in single and dual processor Socket 8 systems, but did not support quad or hexa processor systems officially, though it could unofficially run in such systems.
Reader's Guide
The Pentium OverDrive series is significant as Intel's primary upgrade solution for aging 486, Pentium, and Pentium Pro systems in the mid-to-late 1990s. For 486 users, the OverDrive offered a substantial performance boost in floating-point-dependent and Pentium-optimized software, despite often underperforming cheaper rivals in synthetic benchmarks. Its real-world performance depended heavily on optimal use of motherboard cache. The 83 MHz version, though expensive at $299, provided a notable upgrade for users running increasingly common Pentium-optimized programs and operating systems. The Pentium II OverDrive for Socket 8 is particularly notable for its use in the ASCI Red supercomputer at Sandia National Laboratories. ASCI Red, which was the first computer to break the teraFLOPS performance mark in late 1996 and held the world's fastest computer position from 1997 to late 2000, had all 4,510 of its computing nodes upgraded from dual Pentium Pro CPUs to dual Pentium II OverDrive CPUs in 1999. This upgrade maintained its TOP500 position until surpassed by IBM's ASCI White in late 2000, and made it the first computer to break over two teraFLOPS at the time of the upgrade. ASCI Red continued using these CPUs until decommissioning in 2006. The Pentium II OverDrive combined attractive aspects of the Pentium II (MMX support, improved 16-bit performance) and the Pentium II Xeon (full-speed L2 cache), a configuration later replicated in mobile and desktop Pentium III cores.
Did You Know?
- The Pentium OverDrive for 486 systems had 32 kB of L1 cache, double the 16 kB on regular P54C Pentium chips.
- The 83 MHz version for 486 systems launched in September 1995 at a price of $299.
- The Pentium II OverDrive for Socket 8 was used in the ASCI Red supercomputer, which was the first computer to break the teraFLOPS performance mark.
- The Pentium OverDrive monitors its fan and will throttle clock speed to prevent overheating if the fan fails.
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