what's up with the turbo button on old PCs what does pressing it actually do and is it true that
turbo mode actually slows down the CPU let's try to figure it out and solve the mystery
the first PC with a turbo button was the eagle turbo XL announced in April 1984. it had an 8
megahertz 8086 processor which they claimed was up to twice as fast as the 4.77 megahertz 8088 used
by the IBM PC, XT, and most other PC clones at the time infoworld magazine wrote that a push of the
button on the front panel next to the stylized racing stripes lights the turbo logo in red and
shifts the computer into turbo drive the change can be accomplished even in the middle of running
a program Eagle computer sales manager Larry Bouffard joked that there's no time to get a cup
of coffee while the turbo sorts a database people who use that time to goof off are in trouble
for those who wanted the advantage of turbo speed without buying a whole new computer in late 1984
orchid technology introduced the PC turbo 186 the first accelerator card for IBM PCs and clones they
said simply install the PC turbo adapter board and orchid's productivity software and your
PC becomes a powerful turbo driven computer or you could replace the motherboard of your IBM
XT with an aftermarket turbo XT motherboard such as this one sold by JDR Microdevices
but the faster speed of turbo mode could cause problems with some software and hardware copy
protected applications like Lotus 1-2-3 might refuse to run games would play too fast and even
worse saving files to disk or transferring them over a modem could result in lost or corrupted
data so many turbo XT systems would boot up in standard 4.77 megahertz speed and then the
user could enable turbo mode by pressing a key combination or typing in a DOS command if they
were sure it wouldn't cause any problems this annoyed Lieutenant Ray P. Stallings
of San Francisco who wrote a letter to PC Magazine in 1987 complaining about having
to press Ctrl Alt Plus to enable turbo mode every time he turned on his computer by then
the compatibility problems had largely been resolved so many computers started coming
with a button allowing you to leave turbo mode in a enabled all the time and then switch off
when needed such as for playing older games now let's go back to the studio and take a look at
a few different PCs from the '80s and '90s with turbo buttons so we can learn how they operate
here's the oldest PC I have with a turbo button it's a Zenith Z-148 from 1986 and
I was getting all ready to demonstrate it for you except the Rifa cap in the power supply
blew just a few minutes before I was ready to start filming it so unfortunately I'll
have to save that demonstration for a later video in their brochure for it Zenith said we
just raised the limit on PC processing speed limits based on the industry standard MS-DOS
operating system the Z-148 PC features a powerful 16-bit Intel 8088 processor when
you run the Z-148 PC at its full 8 megahertz it proves I think they meant provides an unsurpassed
60% faster rate than comparable PC models and this unmarked button on the front panel
controls the CPU speed if you leave it popped out like this it runs at 4.77 megahertz the
same speed as the original IBM PC and if you push it in you can hear click if you push it
in it runs at eight megahertz so this is an early example of a turbo button from 1986.
now here is a typical early to mid '90s mini tower PC on the front panel you can see it as
a reset button a turbo button which clicks in and out indicator LEDs for power turbo and hard
disk drive access a knockout plug for where a CPU speed readout LED would have gone if this
was equipped with it but it doesn't have it so just a plastic panel there and finally a key
lock which doesn't actually physically lock the case instead it locks out access to the keyboard
so if you have this in the locked position nobody can type anything on the keyboard
it has a 33 megahertz 486SLC/E processor designed by Cyrix and manufactured by Texas Instruments and
on the motherboard you can find the typical pinouts for the key lock and power led the
speaker the reset button the turbo LED and the turbo switch but you can see the connector going
to the turbo switch has three wires on it while the pin header on the motherboard for the turbo
switch only has two pins on it so there's two possible ways to connect the turbo switch
now here's what happens if I turn it on with the gray and black
wires going from the turbo button to the motherboard pin out for the turbo switch
with the turbo button not pushed in you can see the turbo indicator is not lit
you can hear the pitch of that memory test when it was starting up now if I push in
the button the turbo indicator LED illuminates and I'll reset it listen to that memory test
notice how much higher pitch that is so even just by listening to the ticking noise that the memory
check during startup makes you can tell whether or not this thing is running at full speed or
low speed but just to verify I'll run a benchmark with the button pushed in and the turbo indicator
LED lit you can see it says 33 megahertz CPU clock and I'll run the landmark speed test
and it says this computer performs like 140 megahertz AT with a 95 megahertz 287. obviously
this is an old version that doesn't properly recognize the 486SLC/E so instead it thinks it's
a 486DX so this is running with the turbo button pushed in and the turbo indicator LED lit and
now I'll run that same benchmark with the button not pushed in and the turbo indicator LED not lit
and listen to that change into beeping and now it says this computer performs like a
25 megahertz AT with a 62 megahertz 287 so this is with the turbo button not pushed in
and this is with the turbo button pushed in to give a better idea of the difference in
performance between turbo mode and non-turbo mode on this system I'll run Norton system
information first here is the CPU speed benchmark with the turbo mode disabled
and it gives it a score of 8 which is similar to a 286 now I'll turn on turbo mode
you can see it jumps up all the way to 54.4 which is quite a bit faster than the 33 megahertz 386 so
this is turbo mode and that is non-turbo mode so this is the way I always had this computer
configured and it's the way it made the most sense to me with the turbo button pushed in
and the Turbo indicator LED lit it's running at the full CPU speed and if I un-push the button
and the Turbo indicator LED is not lit you can see it's running a lot slower now
but what happens if we change that connection to the turbo button so that the gray and yellow
wires are connected instead of the black and gray wires now if I turn it on with the turbo
button pushed in you can see the turbo LED is not lit and listen to the memory check
you can hear that lower pitch which means it's not running in turbo mode and now if I un-push
the turbo button the light comes on now if I reset it listen to that memory test again
a higher pitch which means it's running in turbo mode now so this is why I think people are getting
confused and thinking that engaging turbo mode slows down your computer because they may have
had their button configured like this where not pushed in is turbo mode but pushed in is non-turbo
mode which does slow down your computer and maybe they had a system which only had the button and
not the indicator LED so then they would think well what's the deal of this you push it in it
makes your computer slower instead of faster but if you have the turbo indicator LED when
it's lit that always means the CPU is running at full speed and if it's not lit that means
it's running its low speed regardless of how you have this button wired
well here it is without the turbo button connected so regardless of whether I have it pushed in
or not it doesn't make any difference it's not connected and I'll turn it on
and you can see it starts up in non-turbo mode so the default on this motherboard
if you don't have a turbo button connected is that it starts up in non-turbo mode so if you
wanted to install this in a case that did not have a turbo button you would need to put a
jumper on that pin header on the motherboard so that it would start up in turbo mode
but even without that turbo button connected I can still switch it between turbo mode and
non-turbo mode with a keyboard command Ctrl Alt and the plus key on the numeric keypad switches
it into turbo mode you can see the LED lit up and you can hear the beep changed pitch and the
landmark CPU speed test and Control Alt and the number keypad minus switches it back to non-turbo
mode so that's how you can switch the turbo mode on and off with the keyboard Control Alt Plus
turns it on control alt minus turns it off here's the manual for a later 486 motherboard
with PCI slots and it matches exactly what I just showed J4 is a two pin connector for
the turbo switch and it says close for a higher speed while open for a slower speed a BIOS hotkey
Control Alt Plus also brings system to a higher speed while Control Alt Minus set system to a
slower speed and they say the turbo indicator LED is on when higher speed is selected
now here's a name brand factory built PC from the '90s with a turbo button it's a Gateway 2000
4DX-33 and this one is a little bit different than what we've seen so far because the turbo button
does not push in and pop out it is a momentary contact button so it's just a toggle and if we run
the landmark speed test on it we get a score of 158 with the turbo mode enabled and the indicator
LED lit and if I push the button to disable turbo mode it drops down all the way to 15.3
so clearly turbo mode with the LED lit is the full CPU speed and non-turbo mode
with the LED not lit is a much slower speed in turbo mode this 486 DX is quite a bit faster
than a 386 running at the same clock speed of 33 megahertz but if I disable turbo mode
it brings it down all the way to about the same speed as a 286 although even
in non-turbo mode some really old DOS games are still a bit too fast to be playable
buttons and turbo indicator LEDs started to disappear from PCs by the mid-1990s because by
then fewer people still had the need to run old speed sensitive hardware and software and CPUs
were getting fast enough that even in non-turbo mode they were often still too fast to play old
DOS games from the '80s plus I think it was simply a matter of cost cutting to eliminate a button and
LED that few people had a need for just like the aforementioned key lock which disappeared
from most computers at the time as well so for example here is a desktop PC case
from the mid-1990s which does not include a turbo button or Turbo indicator LED although unusually
for the time it still has the CPU speed readout which is a full three-digit readout on this one
because a lot of these were only two digits and once CPU speeds reached 100 megahertz all
of them suddenly became obsolete I remember seeing computers which had a 100 megahertz
CPU but only a two-digit display so usually they either made it read 99 or they just made it read
HI for turbo mode and LO for non-turbo mode or sometimes they simply left it blank entirely
however the motherboard in this computer which is one of those infamous PC Chips
M919 VIP motherboards with fake cache still has the capability of using a turbo indicator LED
and a turbo button so what I've done temporarily is connected the hard drive indicator LED to the
turbo indicator LED pinout on the motherboard and even though we don't have a turbo button
on this case the keyboard commands I mentioned earlier still work so if I press Ctrl Alt Minus
you can see the indicator turned off because we are now running in non-turbo mode and if I
press Ctrl Alt Plus it comes back on and we're now running in turbo mode again
and if we look at the manual for this motherboard board
but you can see the default for the turbo switch connector is the opposite of what we
saw with that previous motherboard in this case shorting the pins puts it in normal
mode or slow CPU speed mode and leaving the pins opon I think they mean open
"what? your arms are wide opon... opon? actually it's pronounced open
you just gotta really enunciate this: open" leaving the pins open with nothing connected to
them puts the CPU in turbo mode so that's the opposite of what we saw before and this was
clearly done with consideration to cases like I just showed which don't even have a turbo
button so that if you didn't have a turbo button connected to the motherboard and you didn't put a
jumper on the pins in this case it would run in turbo mode instead of running in normal mode
and if I run the PC Tools relative CPU performance index it gives a score of 226.1 and
now in non-turbo mode our PC Tools performance index has dropped all the way down to 19.2
the Pentium era was truly the end of the line for Turbo buttons and turbo LEDs on computer
cases a few motherboards still supported them such as the one in this Cyrix 6x86
system the manual for the motherboard in this system still mentions the turbo LED indicator
right here J3 turbo LED connector but it doesn't even mention the turbo switch connector even
though they show it on the layout of the board most of the time pressing the turbo button did
nothing except turn the turbo LED on and off it made absolutely no difference in the computer's
performance or sometimes the turbo button was repurposed for other functions such as in this
case pressing it causes the computer to go into sleep mode and pressing it again wakes it up
now let's look at something the people who write Wikipedia articles and tech
blogs have apparently never heard of it's called a book
this is Upgrading PCs Made Easy written by Bud and Alex Aaron and published by Osborne McGraw-Hill in
1991 and right here on page 11 it talks about the turbo mode switch it says this is mostly a catchy
advertising term since it does not actually speed up your computer if you press it instead it slows
your computer down if you don't press it and they talk about compatibility if the original
IBM PC and that some computer programs would not work properly if your system runs too fast
here's another explanation from the book Information Technology and Business Management
written by Dr. Mukesh Dhunna it says turbo switch if you're using a PC that has two different speeds
of operation then you will find a turbo switch on the front side of your PC this switch changes the
speed from a low value to a high value and hence the name turbo pressing this switch on will result
in running the computer at its highest speed and here in lesson 2 of The Whiz Kids Computer
Literacy Program it gives a much more succinct explanation it says turbo switch activating this
switch will make your computer work faster and Building a PC for Dummies 5th Edition which
was written when most people no longer had a need for the turbo button mentions don't
forget that turbo button if your PC does have a turbo button you might boot your computer one day
and find that everything suddenly seems to run slower if so your first suspect should be that
doggone turbo button if your PC isn't running in turbo mode it's forced to run more slowly
and I'm sure some stubborn people might think that these authors all got it wrong so I found
the data sheet for the Intel 486SL microprocessor and it says right here turbo mode is defined as
the CPU executing at full speed the default speed for the system so that's straight from
the horse's mouth Intel says that turbo mode is the CPU executing at full speed
I know the Wikipedia article about turbo buttons is saying that an authoritative source is required
well I think this is about as authoritative as you can get directly from Intel
so if you want to argue with what Intel wrote 30 years ago go right ahead but for
the rest of us I think this has definitively solved the mystery about what the turbo button
does and we've debunked the myth that turbo mode slows down the computer