(^186) PC Hardware: A Beginner’s Guide
FC-AL uses fiber optic cables to connect the disk drives to the controller and the PC. It
transfers data at the rate of over 100MB per second. Fiber channel can support up to 127
devices, and because it uses fiber optic cabling, the devices can be as far as 10 kilometers
apart. FC-AL devices can be hot-swapped, which means that they can be inserted and
removed without interfering with the operation of the system.
System Bus Interface
Hard disk interfaces also interface with the rest of the PC system on one of the system’s
I/O bus architectures. Commonly, the available buses arePCI (Peripheral Component
Interconnect), VLB (VESA Local Bus), or theISA (Industry Standard Architecture)bus.
IDE/ATA and SCSI require faster transfer modes over a local bus, which means they
use either the PCI or VLB buses. Where most older PCs and hard disks (ST506/412 and
ESDI) used a dedicated hard disk controller mounted into a system bus slot, newer PCs
use the PCI bus on motherboards that typically have two IDE/ATA channels and possibly
one EIDE channel built into the motherboard itself.
See Chapter 11 for more information on the system bus structures.Transfer Protocols
Dataistransferredfromthediskdrivetosystemmemoryusingoneoftwotransfermodes: Programmed I/O (PIO) PIO is the data transfer protocol used on most older
disk drives. The PC’s CPU executes all of the instructions used to move data
from the disk to the PC.
Direct Memory Access (DMA) DMA transfers data directly to or from
memory, without involving the CPU in the transfer, which frees the CPU
to perform other tasks. The device’s built-in controller handles the transfer
without help from the CPU. Nearly all new IDE/ATA hard disks support
DMA, which is commonly used in floppy disks, tape drives, and sound cards.Data Addressing
Data is addressed on the disk using two methods: CHS (cylinder-head-sector) This is the data addressing method used on most
IDE drives. It locates data on the disk by its cylinder (track), head (meaning
platter side), and sector on the track. For example, a file could begin on cylinder
250, head 4, and sector 33. The number of cylinders, heads, and sectors on your
hard disk can be found in the BIOS setup configuration data.
LBA (logical block address) In this method of data addressing, each sector on
the disk is assigned a sequential logical block number. LBA addressing simply
lists a single logical location for each file. LBA is used on SCSI and EIDE drives.