7.6.1.0820 BUFFER BLOCK

a-addr is the address of the first character of the block buffer assigned to block u. The contents of the block are unspecified. An ambiguous condition exists if u is not an available block number.

If block u is already in a block buffer, a-addr is the address of that block buffer.

If block u is not already in memory and there is an unassigned buffer, a-addr is the address of that block buffer.

If block u is not already in memory and there are no unassigned block buffers, unassign a block buffer. If the block in that buffer has been UPDATEd, transfer the block to mass storage. a-addr is the address of that block buffer.

At the conclusion of the operation, the block buffer pointed to by a-addr is the current block buffer and is assigned to u.