Question

10.a. Consider a file F which contains a sequence of variable-length records, with record's length (n) as following: RI n-4 R6 R2 n=5 R3 n=2 R4 n=4 R5 n=2 n=7 Assume there is a disk X with 3 equal blocks, each block with length 10. By maintaining the order of records' sequence, show how the set of records of file F can be arranged in the blocks in X based on the following blocking methods: Answer: Variable Blocking Spanned Disk X Block 2 Block 1 Block 3 Variable Blocking Unspanned Disk X Block 2 Block 1 1 Block 3 10.b. Based on the answers in (10)(a)(i) dan (10)(a)(ii), explain why variable blocking unspanned is less efficient compared to variable blocking spanned.

Answer 1

Solution: The solution of Q.10(a)(1) is already given in question you can see but record is not assigned in variable blocking spanned and variable blocking unspanned method. So here we assigned the records in variable blocking spanned and variable blocking unspanned method. And discuss why variable blocking unspanned is less efficient compared to variable blocking spanned.

Variable blocking spanned:

                                                                                   Disk X

     Block 1(length =10)                            Block2(length =10)                          Block3(length =10)

R1(n=4)

R2(n=5)

R3(n=1)

R3(n=1)

R4(n=4)

R5(n=2)

R6(n=3)

R6(n=4)

6B wastage

Variable blocking unspanned:

                                                               Disk X

    Block 1(length =10)                         Block2(Length =10)                            Block3(length =10)

R1(n=4)

R2(n=5)

1B wastage

R3(n=2)

R4(n=4)

R5(n=2)

2B wastage

R6(n=7)

3 B wastage

In variable blocking spanned we can span the records in different block Means portion of a single record may accupied in different blocks due to their large size, such records are called Spanned Records. So, the memory wastage is less than variable blocking unspanned. As you see in figure, Memory wastages in only one blocks 3.

But in variable blocking unspanned we cannot spanned the records in different block. So, the memory wastage is more than variable blocking spanned. You can see in figure Memory wastages accrues in each block 1,2 and 3 also.

If we want to add some additional records the we can lie in remaining size of block 3 in spanned but in unspanned we require an extra block for it.so the increasing no of blocks makes more difficulty to accessing it and more time required for it. But it is not happening in spanned so we can say that variable blocking unspanned is less efficient compared to variable blocking spanned.

figure:

Variable blocking spanned: Disk X Block 1(length =10) Block2(length =10) Block3(length =10) R1(n=4) R2(n=5) R3(n=1) R3(n=1) R4(n=4) R5(n=2) R6(n=3) R6(n=4) 6B wastage Variable blocking unspanned: Disk X Block 1(length =10) Block2(Length =10) Block3(length =10) R1(n=4) R2(n=5) 1B wastage R3(n=2) R4(n=4) R5(n=2) 2B wastage R6(n=7) 3B wastage