There are three different Flash sizes available on the different SAM3U versions, ranging from 256 kB to 64 kB. The 256 kB version is in fact a dual-plane Flash, with 2 x 128 kB Flash seen as contiguous by the core. Single cycle access is possible up to 24 MHz in worst case. It also embeds several buffers for code and data read optimizations which allow to fetch sequential code in single cycle up to 96 MHz. There is a unique 128-bit factory programmed ID for each device. The automatic sleep mode feature is enabled when Flash is accessed at low speed (below 1 MHz) and ensures that power consumption is reduced.