I am having some confusion in understanding the meaning of the term data item .
when we write
READ(A)
A=A-10
WRITE(A)
Now I am unable to get one point here that when we have a file consisting of various blocks and those blocks consisting of various record and when we say that we are accessing a particular data item for reading then is this data item is a record or some particular field inside that record .
And major confusion is that how can we simply read a field from a record during disk access , since disk access is expensive hence we must be able to fetch the entire block from the disk , but we write only this statement like :
READ(A) , is this block or only a single attribute ?