Class Disk

java.lang.Object
  |
  +--Disk

public class Disk

extends java.lang.Object

implements java.lang.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 track 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.
protected boolean	busy An indication of whether an I/O operation is currently in progress.
protected int	currentBlock Current location of the read/write head
protected static int	DELAY_PER_TRACK Seek time per track, in ms
int	DISK_SIZE Total size of this disk, in blocks.
protected int	targetBlock The block number to be read/written by the current operation.
static int	TRACK_SIZE The size of a track, in blocks.
protected static int	TRANSFER_TIME Minimum time to transfer one block of data, in ms

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.
protected void	delay(int targetBlock) Sleeps for a while to simulate the delay in seeking and transferring data.
protected void	finishOperation() Indicates to the CPU that the current operation has completed.
void	flush() Saves the contents of this Disk.
void	run() This method simulates the internal microprocessor of the disk controler.
int	trackOf(int blockNumber) Computes the track number of a disk block.
protected void	waitForRequest() Waits for a call to beginRead or beginWrite.

Methods inherited from class java.lang.Object

clone, equals, finalize, 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.

TRACK_SIZE

public static final int TRACK_SIZE

The size of a track, in blocks.

DISK_SIZE

public final int DISK_SIZE

Total size of this disk, in blocks.

DELAY_PER_TRACK

protected static final int DELAY_PER_TRACK

Seek time per track, in ms

TRANSFER_TIME

protected static final int TRANSFER_TIME

Minimum time to transfer one block of data, in ms

currentBlock

protected int currentBlock

Current location of the read/write head

busy

protected boolean busy

An indication of whether an I/O operation is currently in progress.

targetBlock

protected int targetBlock

The block number to be read/written by the current operation. Only meaningful if busy == true.

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. If the DISK file is smaller than the simulated disk, only the start of the simulated disk is initialized; if the DISK file is bigger, the excess part of the DISK file is ignored. 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.

trackOf

public int trackOf(int blockNumber)

Computes the track number of a disk block. This simulated disk does not simulate rotational latency, so latency is determined only by the number of tracks traversed and all blocks on the same track are considered equally far away.

Parameters:

blockNumber - a block (sector) number.

Returns:

the track number of the block.

delay

protected void delay(int targetBlock)

Sleeps for a while to simulate the delay in seeking and transferring data.

Parameters:

targetBlock - the block number to which we have to seek.

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.

waitForRequest

protected void waitForRequest()

Waits for a call to beginRead or beginWrite.

finishOperation

protected void finishOperation()

Indicates to the CPU that the current operation has completed.

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 java.lang.Runnable