2 System Board

Devices on the PCI Bus

Transfer Rates Versus Modes of Operation

to a channel, it should be in the master position (the connector that is closest to the system board, unless the markings on the cables state otherwise).

It is possible to mix a fast and a slow device, such as a hard disk drive and a a CD-ROM, on the same channel without affecting the performance of the fast device. The BIOS sends a command to each drive to determine, automatically, the fastest configuration that it supports. However, in general, the primary channel cable is recommended for hard disk drives, and the secondary channel cable for CD-ROM drives.

The controller supports 32-bit Windows I/O transfers. Five PIO modes, and three DMA modes are supported. The five supported PIO modes allow the following transfer rates.

Mode

0

1

2

3

4

 

 

 

 

 

 

Cycle time (ns)

600

383

240

180

120

 

 

 

 

 

 

Transfer rate (MB/s)

3.33

5.22

8.33

11.1

16.7

 

 

 

 

 

 

The three DMA modes allow the following transfer rates:

Mode

0

1

2

 

 

 

 

Cycle time (ns)

480

150

120

 

 

 

 

Transfer rate (MB/s)

4.2

13.3

16.7

 

 

 

 

Disk Capacity Versus Modes of Addressing

The amount of addressable space on a hard disk is limited by three factors: the physical size of the hard disk, the addressing limit of the IDE hardware, and the addressing limit of the BIOS. The Extended-CHS addressing scheme allows larger disk capacities to be addressed than under CHS, by performing a translation. If the Setup field has been set to automatic, the logical block addressing (LBA) mode will be selected for each device that supports it.

 

Cylinders per

Heads per

Sectors per Track

Bytes per

Bytes per

 

Device

Cylinder

Sector

Device

 

 

 

 

 

 

 

 

 

CHS

64

16

1024

512

528

M

 

 

 

 

 

 

 

ECHS

64

256

1024

512

8.4

G

 

 

 

 

 

 

LBA

-

-

256 M (=228)

512

137 G

35