F543 COMPUTER SCIENCESPOOLING AND FILE ALLOCATION TABLES

VIRTUAL MEMORY SOUNDS PRETTY USEFUL, BUT DOES IT HAVE ANY OTHER USES?

• Spooling is used when the rate the processor can send data is faster than the rate a peripheral device can output it.

• For example, consider a printer.

• It might be able to print 20 pages per minute, a third of a page per second. However, the processor is cable of sending pages much faster than this.

• This is known as speed mismatch.

• To prevent the processor from being "held up" by the printer (or another peripheral), the print data is saved to secondary storage.

• It is then retrieved and sent to the printer when the printer is ready – in the mean time the processor can work on higher priority tasks.

CAN YOU PROVIDE A DIAGRAM TO HELP EXPLAIN SPOOLING

• Sure!

Secondary storage

Processor

Peripheral device

Processor sends data to peripheral device

The speed of data transfer is faster than the peripheral devices working speed

FILE ALLOCATION TABLES

• The operating system has the task of creating and managing

the file system on its hard disk drives.

• There are a number of filing methods an operating system can

use to organise files and folders. One of them is called the FAT

filing system. Otherwise known as the 'File Allocation Table'

system.

OK, BUT HOW?

• All data on a hard disk is stored in 'Sectors'. Sectors are

grouped together into 'clusters‘.

• The cluster is the minimum unit of storage a file can use. If the

file is actually smaller than a cluster, then the unused space is

wasted. A typical cluster size is 4kb but can vary from 2kb to

32kb. Each cluster is numbered so the FAT can locate a

particular cluster on the hard disk.

IS THERE ANY WAY TO REPRESENT THIS ON A DIAGRAM?

• Yes.