Class Disk

Object
  Disk

All Implemented Interfaces:

Runnable

public class Disk
extends Object
implements Runnable

A software simulation of a Disk.

You may not change this class.

This disk is slow and ornery. It contains a number of blocks, all BLOCK_SIZE bytes long. All operations occur on individual blocks. You can't modify any more or any less data at a time.

To read or write from the disk, call beginRead() or beginWrite(). Each of these functions will start the action and return immediately. When the action has been completed, the Disk calls Kernel.interrupt() to let you know the Disk is ready for more.

It may take a while for the disk to seek from one block to another. Seek time is proportional to the difference in block numbers of the blocks.

Warning: Don't call beginRead() or beginWrite() while the disk is busy! If you don't treat the Disk gently, the system will crash! (Just like a real machine!)

This disk saves its contents in the Unix file DISK between runs. Since the file can be large, you should get in the habit of removing it before logging off.

See Also:

Kernel

Field Summary

static int	BLOCK_SIZE The size of a disk block in bytes.
int	DISK_SIZE Total size of this disk, in blocks.

Constructor Summary

Disk(int size)
Creates a new Disk.

Method Summary

void	beginRead(int blockNumber, byte[] buffer) Starts a new read operation.
void	beginWrite(int blockNumber, byte[] buffer) Starts a new write operation.
void	flush() Saves the contents of this Disk.
void	run() This method simulates the internal microprocessor of the disk controler.

Methods inherited from class Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

BLOCK_SIZE

public static final int BLOCK_SIZE

The size of a disk block in bytes.

See Also:

Constant Field Values

DISK_SIZE

public final int DISK_SIZE

Total size of this disk, in blocks.

Constructor Detail

Disk

public Disk(int size)

Creates a new Disk. If a Unix file named DISK exists in the local Unix directory, the simulated disk contents are initialized from the Unix file. It is an error if the DISK file exists but its size does not match "size". If there is no DISK file, the first block of the simulated disk is cleared to nulls and the rest is filled with random junk.

Parameters:

size - the total size of this disk, in blocks.

Method Detail

flush

public void flush()

Saves the contents of this Disk. The contents of this disk will be forced out to a file named DISK so that they can be restored on the next run of this program. This file could be quite big, so delete it before you log out. Also prints some statistics on disk operations.

beginRead

public void beginRead(int blockNumber,
                      byte[] buffer)

Starts a new read operation.

Parameters:

blockNumber - The block number to read from.

buffer - A data area to hold the data read. This array must be allocated by the caller and have length of at least BLOCK_SIZE. If it is larger, only the first BLOCK_SIZE bytes of the array will be modified.

beginWrite

public void beginWrite(int blockNumber,
                       byte[] buffer)

Starts a new write operation.

Parameters:

blockNumber - The block number to write to.

buffer - A data area containing the data to be written. This array must be allocated by the caller and have length of at least BLOCK_SIZE. If it is larger, only the first BLOCK_SIZE bytes of the array will be sent to the disk.

run

public void run()

This method simulates the internal microprocessor of the disk controler. It repeatedly waits for a start signal, does an I/O operation, and sends an interrupt to the CPU. This method should not be called directly.

Specified by:

run in interface Runnable