Why Did the Turbo Button Slow Down Your PC in the ’90s?

A vintage PC Turbo button.Benj Edwards

In the 80s and 90s, many IBM PC clones included a button on the case called “Turbo” that actually slowed down your PC when you pressed it. We explore why it was necessary, what it did and who put it in the first place.

Speedy Clones attack

The first one IBM personal computer, released in August 1981, included an 8088 processor operating at 4.77 MHz. Competitors, like Compaq, quickly reverse engineered the machine, MS-DOS operating system and created their own IBM PC compatible computers.

A man working on an IBM PC 5150.A marketing photo of the IBM PC 5150, circa 1981. IBM

These clones often added functionality that was missing from the IBM PC series at a much lower price. Some included built-in peripheral ports, more RAM, and real-time clocks, while maintaining software compatibility. Some of the early manufacturers of clones went even further and produced much faster machines. For example, several models used an Intel 8086 8 MHz chip which was about two to three times faster than the original processor on the IBM PC.

New PCs were too fast for existing applications

This increase in speed introduced a problem. Most application developers in the early 1980s did not anticipate that the IBM PC would become a backwards compatible platform or that its performance would skyrocket. As a result, most software applications and games created for the IBM PC have been specifically tuned to the 4.77 MHz clock speed of the 5150. If someone tried to run them at faster speeds (like 8 MHz or higher), some of these early programs became unstable. Many games quickly became unplayable.

The first IBM PC CPU accelerator cards solved this problem by including a physical switch on the back, allowing the machine to switch between maximum accelerator speed and compatibility mode at 4.77 MHz. On some PC clones, you can even use BIOS-level keyboard shortcuts, such as Ctrl + Alt + Plus or Ctrl + Alt + backslash, to switch between processor speed modes.

However, these modes were not yet called “turbo”; but this marketing innovation was upon us.

Enter the Eagle Turbo PC (and the Turbo button)

The Eagle Computer logo.

Around July 1984, in Los Gatos, California, a manufacturer of PC clones called Eagle computer introduced a new line of products called Eagle PC Turbo. Each model included a fast 8086 8 MHz processor and a new feature: a Turbo button on the front panel. When pressed, it toggles the computer between clock speeds of 8 and 4.77 MHz.

The press has noted how great Eagle’s innovation was at the time. In his issue of December 11, 1984, PC Magazine springs on the speed of the Eagle PC Turbo:

“In fact, it is so fast that Eagle had to include a push button on the front panel to slow operations down by inserting additional wait states when necessary for PC compatibility.”

This article also presents the only known photo of the Eagle PC Turbo and its Turbo seminal button available on the Web.

PC Tech Journal also noted the arrival of the Eagle PC Turbo line in its July 1984 issue:

“The machine based on 8086 has a” Turbo “button on the front panel. Press it and the machine goes from the PC / XT compatible clock speed from 4.77 Mhz to 8 Mhz.”

Another manufacturer may use the term “Turbo Button” before the Eagle computer. However, after exhaustive research in the computer periodicals of the early 1980s, we think this is unlikely.

The word “turbo” is short for “turbocharger”, which accelerates internal combustion engines. In the 1980s, it was common for commercial marketing departments to apply the word “turbo” to products to denote additional speed or power. No manufacturer would ever include a large button labeled “Slow” on the front of their new fast PC, so “Turbo” was a smart choice on Eagle’s part.

A few years after the introduction of the Eagle Turbo PC (when accelerated PC clones became inexpensive enough to be consumer goods), “turbo” suddenly became the generic term in the industry for this slowdown function. processor. This is likely due to the fact that other PC manufacturers have copied it and placed it in off-brand PC cases and motherboards.

In 1988, Turbo buttons were everywhere.

Turbo buttons exploded in popularity

Pictures of PC with turbo buttons in the collection of Benj EdwardsThree examples of generic 386 era PC cases with turbo buttons. Benj Edwards

From the early to mid-1990s, average processor clock speeds for IBM PC-compatible computers jumped into the stratosphere. They went from around 16 MHz to around 100, with stops at 20, 33, 40 and 66 MHz along the way. This made the Turbo buttons absolutely essential for playing the first PC games, many of which were less than a decade old at the time.

Some PC cases even included a two-digit segmented LED display that toggled between turbo and non-turbo digital clock speeds each time the Turbo button was pressed. Interestingly, this feature has often been configured on the LED module. Thus, these could be configured to display any number, which proves that this is yet another marketing gadget.

Modern software left the Turbo button behind

At one point, most application developers started writing new software with the thought of increasing processor speed. These programs would measure the system clock speed and introduce a delay, if necessary, for the program to continue running at the expected rate. It worked even if you ran the program on a much faster processor introduced after this particular software.

As these programs became more widespread and the legacy software of the 1980s became less commonly used, fewer and fewer people used the Turbo buttons.

Around the The Pentium era Between the mid-to-late 1990s, many generic PCs and buildable PC cases stopped including Turbo buttons. In the low-margin world of basic PCs at that time, all of the foreign features generally bit the dust quickly enough to cut costs.

In 2000, the Turbo button had practically disappeared on new machines. Back then, if people wanted to slow down DOS programs, they often used software applications, like Mo’Slo or CPUKILLER instead.

The Age of Turbo was over, but at the consumer level CPU overclocking was just around the corner. He proved once and for all that a real “turbo mode” that actually accelerates the machines, instead of slowing them down, is ultimately possible.

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