Operation Manual
the chip in other ways as well. In particular, it allows you to alter the speed at which the chip runs, increasing its performance at
the expense of the part’s lifespan—a process known as overclocking.
Adjusting any of the settings listed in this section can result in damage to your Pi. In particular, changing settings corresponding to memory, GPU
or CPU voltages will set a fuse in the chip, which invalidates the Raspberry Pi’s warranty even if the setting is returned back to normal before any
damage is done. Damage caused when using these settings will not be put right by the Raspberry Pi Foundation or by the retailer from whom you
purchased your Pi. If in doubt, don’t alter these settings: the performance gains through overclocking are rarely worth the risk to the Pi.
The BCM2835 multimedia processor at the heart of the Pi is a system-on-chip (SoC) design split into two main parts: the
graphics processor (GPU) and the central processor (CPU). Simply put, the CPU handles all the day-to-day processing tasks
while the GPU handles drawing things on the screen, in both 2D and 3D.
Using config.txt, you can overclock one or both parts of the BCM2835. You can also increase the speed at which the
memory module—located on top of the chip in a package-on-package (PoP) mounting format—operates.
Boosting the operating frequency of these components results in a small increase in the Pi’s performance: an increase to the
GPU’s clock frequency means that 3D graphics (such as game graphics) will render at a faster pace, and video will be decoded
quicker for smoother playback; and increasing the CPU’s clock frequency will boost overall performance of the device, as will
increasing the memory’s frequency.
The reason the Pi isn’t provided with higher operating speeds in the first place is related to the chips’ lifespan. The BCM2835 is
rated by its manufacturer, Broadcom, to operate at a speed of 700 MHz. Increasing the speed above this officially-rated level
may work, but it will also have a deleterious effect on the lifespan of the chip. Unlike a desktop processor, SoC designs rarely
have much headroom for overclocking.
Overclocking Settings
If you’re willing to take the risk of breaking the Pi—a process known as bricking in embedded device circles—for the sake of a
small performance gain, there are settings in config.txt which can help. The following settings control performance of the Pi’s
SoC:
• arm_freq—Sets the core clock frequency of the CPU portion of the BCM2835, for a boost in general-purpose
performance. The default speed is 700 MHz.
• gpu_freq—Sets the clock frequency of the GPU portion of the BCM2835, for a boost in graphics performance across all
operations. The default speed is 250 MHz. Additionally, you can adjust individual portions of the GPU’s hardware using the
following options:
• core_freq—Sets the core clock frequency of the GPU, leaving the other frequencies alone, to improve overall GPU
performance. The default speed is 250 MHz.
• h264_freq—Sets the clock frequency of the GPU’s hardware video decoder to improve playback of H.264 video data.
The default speed is 250 MHz.
• isp_freq—Sets the clock frequency of the image sensor pipeline, for improving the capture rate of connected video
hardware (such as a camera). The default speed is 250 MHz.
• v3d_freq—Sets the clock frequency of the GPU’s 3D rendering hardware, for a boost in visualisation and gaming
performance. The default speed is 250 MHz.
• sdram_freq—Sets the clock speed of the random access memory (RAM) chip on the Pi, to give the entire system a small
increase in performance. The default speed is 400 MHz.
• init_uart_clock—Sets the default clock speed of the Universal Asynchronous Receiver/Transmitter (UART), used to
control the serial console. The default is 3000000, which sets a speed of 3 MHz. Altering this is likely to have little effect
beyond corrupting the output of the serial console.
• init_emmc_clock—Sets the default clock speed of the SD card controller. The default is 80000000, which sets a speed of
80 MHz. Increasing this value can result in faster reading and writing from the SD card, but can also lead to data corruption.
As an example, to overclock the CPU to 800 MHz, the GPU to 280 MHz and the RAM to 420 MHz, enter the following
options into config.txt, one per line:
arm_freq=800
gpu_freq=280
sdram_freq=420
As with adjusting the display configuration, any changes made regarding overclocking won’t take effect until the Pi is restarted.