We're pointing to a block of data; that's the 4 KiB. You have 12 direct pointers — that's the "12". The "1024" appears to be the single indirect pointers: it s

We're pointing to a block of data; that's the 4 KiB. You have 12 direct pointers — that's the "12". The "1024" appears to be the single indirect pointers: it seems like the inode only has 1 "single indirect pointer", so that points to a block's worth of pointers. (Hence the "indirect" part.) A block in this design is 4 KiB, and a pointer in this design is 4 B, so the block of pointers will hold 4 KiB / (4 B/pointer) = 1024 pointers — that's the "1024".