NAND Flash Technical Notes
Identifying Initial Invalid Block(s)
Initial Invalid Block(s)
Initial invalid blocks are defined as blocks that contain one or more initial invalid bits whose reliability is not guaranteed by Samsung.
The information regarding the initial invalid block(s) is called the initial invalid block information. Devices with initial invalid block(s)
have the same quality level as devices with all valid blocks and have the same AC and DC characteristics. An initial invalid block(s)
does not affect the performance of valid block(s) because it is isolated from the bit line and the common source line by a select transistor.
The system design must be able to mask out the initial invalid block(s) via address mapping. The 1st block, which is placed on
00h block address, is guaranteed to be a valid block up to 1K program/erase cycles with 1bit/512Byte ECC.
All device locations are erased(FFh) except locations where the initial invalid block(s) information is written prior to shipping. The initial
invalid block(s) status is defined by the 1st byte in the spare area. Samsung makes sure that either the 1st or 2nd page of every
initial invalid block has non-FFh data at the column address of 2048. Since the initial invalid block information is also erasable in
most cases, it is impossible to recover the information once it has been erased. Therefore, the system must be able to recognize the
initial invalid block(s) based on the original initial invalid block information and create the initial invalid block table via the following
suggested flow chart(Figure 3). Any intentional erasure of the original initial invalid block information is prohibited.

Error in write or read operation
Within its life time, additional invalid blocks may develop with NAND Flash memory. Refer to the qualification report for the actual
data.The following possible failure modes should be considered to implement a highly reliable system. In the case of status read failure
after erase or program, block replacement should be done. Because program status fail during a page program does not affect
the data of the other pages in the same block, block replacement can be executed with a page-sized buffer by finding an erased
empty block and reprogramming the current target data and copying the rest of the replaced block. In case of Read, ECC must be
employed. To improve the efficiency of memory space, it is recommended that the read or verification failure due to single bit error be
reclaimed by ECC without any block replacement. The said additional block failure rate does not include those reclaimed blocks