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That way, whenever we need to write 1s to a block where it contains 0s, we just use the
next available physical page in flash and then set the cell in the virtual table to reference
the new block [Fig 5.7].
This technique has another advantage, because we end up using different physical blocks
whenever we need to overwrite 0s with 1s, we reduce the number of times the same
physical block is modified and that helps the Flash storage last longer.
In practice, the table of virtual block numbers itself must be stored in flash memory too and
the Flash table suffers from the same problem - how do we modify the values in the table?
The solution is to realize that every time we need a new physical block, it will be the block
immediately after the previous one. Consider the example in Fig 5.6 and 5.7; first virtual
block 2 was written (to physical page 0); then virtual block 3 (to physical page 1); then vir-
tual block 4 (to physical page 3) etc
used we can, instead store the virtual block numbers that use them [ Fig 5.8].
3
Notice Physical page 2 was never used - in reality it would have been used and then superseded by an-
other in the same way Physical page 3 was later superseded by physical page 7.
Fig 5.6
Fig 5.7
3
. Since we know the order that the physical blocks are
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