# setBytes(_:length:attributeStride:index:) Copies data with a given stride directly to the GPU to populate an entry in the buffer argument table. ``` func setBytes(_ bytes: UnsafeRawPointer, length: Int, attributeStride stride: Int, index: Int) ``` ## Parameters `bytes` A pointer to the memory where the data to copy starts. `length` The number of bytes to copy. `stride` The number of bytes between the start of one element and the start of the next. `index` The index the data binds to in the argument table. ## Discussion> Important: > This method only works for data smaller than 4 kilobytes that doesn’t persist. Create an ``doc://com.apple.metal/documentation/Metal/MTLBuffer`` instance if your data exceeds 4 KB, needs to persist on the GPU, or you access results on the CPU. This method allows Metal to copy data directly onto the GPU, rather than creating a new [`MTLBuffer`](/documentation/Metal/MTLBuffer) instance and binding it. Binding data directly can improve performance, especially when making many small allocations. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)