The Storage Controller
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Every computer uses several storage devices that hold data permanently
(in contrast to RAM, which stores data volatile).
To control which portion of data goes to what storage medium a
storage controller is needed.
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The storage controller consists of two parts:
- the slots (where the data cable to the different devices are
plugged on), and
- the controller chip (where the decisions of directing the traffic
are made).
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Advance 2941UW SCSI Controller, Business Edition
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For PCs there are two kinds of storage controllers: IDE controllers and
SCSI controllers.
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The Integrated Drive Electronics (IDE) controller is most common, and it
is onboard on most motherboards. It can
accomodate up to two devices on one 34-pin cable (floppies and floppy
streamers), and another four devices on two 40-pin-cables (hard disks,
CD-drives, etc). IDE is only usable for internal devices.
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The Small Computer Systems Interface (SCSI) controller is usually not
onboard but on an extra expansion card. Its simplest form accomodates
up to 7 devices on a single string of internal 50-pin-cable, or on a
chain of external cables, or in a combination of both.
So SCSI is usable for internal devices (hard disks, CD drives) as well
as external devices (Scanners, portable hard disks, etc).
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