Ultra-ATA/33-66-100
As always, people wanted higher data transafer rates from their hard drives. This will never change. Ultra-ATA is the type of ATA that delivers the increased speeds. It is an implementation of ATA/ATAPI-4. It provides faster transfer by using advances in the bus mastering DMA technology. This is the primary reason why this is usually called UltraDMA, or UDMA. UDMA requires not only drive support, but also controller and BIOS support, in order to operate. Each successive UDMA speed requires this level of support for this speed. For example, if your BIOS has support for UltraATA/66, it will support UltraATA/33, but not UltraATA/100.
UltraATA/33 was the first speed using this technology. It supports a 33 Mbps transfer rate and uses a standard 40-pin IDE cable. UltraATA/66 handles a 66 Mbps transfer speed, but uses a 40-pin, 80-wire cable to connect to the controller. These cables are the same width, but each individual wire is thinner. These cables are provided with the drive when you buy it. UltraATA/100 is the latest implementation (as of this writing), and as you might have predicted, supports a 100 Mbps transfer. I should mention that with all of these modes, the transfer rate is the peak rate, and you should not expect data to constantly travel at those speeds. In order to use these modes, DMA must be enabled in the operating system.
Cable Configuration
Cable configuration is quite simple with the ATA IDE interface. There is a single cable with three connectors on it. One of these connectors plugs into the IDE connector on the motherboard or I/O adapter card. The other two attach to the drives. On most setups, one end of the cable is attached to the IDE controller. The middle connector attaches to the secondary drive, if there is one. The other end is attached to the primary drive, or drive C:. There is no termination of the chain required, as there is in SCSI. A termination circuit is built into the drive. Sometimes, the D: drive is on the end while the C: drive is connected in the middle. This usually works fine since the master/slave relationship is determined by the jumpers, not the cable. Other setups have the middle connector attached to the motherboard, with the cable ends attached to the drive: a sort of Y arrangement. This is done in many systems, but must be handled with care because the master/slave relationship is then determined by position on the cable. On the Y setup, a special signal called the CSEL, carried on pin 28, defines primary or secondary. If the CSEL circuit is closed, the drive is primary. If it is open, the drive is secondary. This is usually done with a small hole pricked through wire 28 on the cable. Whichever drive is connected to that section of cable is then drive D:. Get it?
Jumper Settings
Most IDE drives come in three configurations: Single drive, master, and slave. These are controlled by a small series of jumpers, usually on the rear of the drive. The single drive setting tells the drive it is alone in the system, and it responds to all commands. If it is configured as a master, this tells the drive there is a slave drive present, and the drive will respond to only master commands. If the drive is configured as a slave, it responds only to slave commands. These jumpers are usually labeled on the drive, so setting them should be no problem.
Some drives also have a “Slave Present” jumper. This is only needed on the master drive, and basically just tells it that it has a partner.
Before the ATA IDE specification, there was no common method of master/slave relationships. Each manufacturer had a different method. For this reason, these drives can be difficult to work with in a two-drive system. Some must work in either a master/slave or slave/master order.
Bus Mastering
Bus mastering is an enhancement for your drive controller interface meant to increase performance. It uses DMA to reduce CPU load. PIO modes are, by nature, more CPU intensive. Most modern PCs support bus mastering. In order to have this support, there are a few necessary things:
- Motherboard must support bus master IDE (sometimes BM-IDE)
- BIOS must support it
- You need an operating system that can multi-task
- A busmastering driver is needed for the OS.
- The EIDE drive must be bus mastering compliant.
Bus master driver problems have been prevalent, though.
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