The Apple S1 is the integrated computer in the Apple Watch, and it is described as a "System in Package" (SiP) by Apple Inc.[7] Samsung is said to be the main supplier of key components, such as the RAM and NAND flash storage, and the assembly itself,[8] but early teardowns reveal RAM and flash memory from Toshiba and Micron Technology.

[3] It uses a customized application processor that together with memory, storage and support processors for wireless connectivity, sensors and I/O constitute a complete computer in a single package.

[9] From reverse engineering, the processor handling the Wi-Fi and Bluetooth is a Broadcom BCM43342[10] and the six-axis gyroscope is from STMicroelectronics.

[2] The SiP in Apple Watch Series 1 is called S1P and looks superficially identical to the S1, but in reality is an S2 minus the on-chip GPS functionality.

The S1 made its first appearance within the Apple Watch, which arrived in April 2015.