Embedded Design Handbook

ID 683689
Date 8/28/2023
Public
Document Table of Contents

3.5.4.2. Disadvantages

A major disadvantage of flash is its write speed. Because you can only write to flash devices using special commands, multiple bus transactions are required for each flash write. Furthermore, the actual write time, after the write command is sent, can be several microseconds. Depending on clock speed, the actual write time can be in the hundreds of clock cycles. Because of the sector-erase restriction, if you need to change a data word in the flash, you must complete the following steps:

  1. Copy the entire contents of the sector into a temporary buffer.
  2. Erase the sector.
  3. Change the single data word in the temporary buffer.
  4. Write the temporary buffer back to the flash memory device.

This procedure contributes to the poor write speed of flash memory devices. Because of its poor write speed, flash memory is typically used only for storing data which must be preserved after power is turned off.