Misc. Hard Disk Trivia

- Out of the box, G5's support only Serial-ATA and Firewire hard-drives.

- IDE and ATA drives are NOT the same thing as Serial-ATA. You want Serial-ATA only for a G5. Serial-ATA is a serial interface that I believe uses an optical cable - so it is completely different from the older ATA port, which is a revamped IDE-style parallel-interface.

- Serial-ATA is a direct serial connection - not a bus like the older IDE where you could daisy chain several devices off the same port. The G5 has 1 extra serial ATA port inside, corresponding to the one empty hard-drive slot internally, thus allowing a max of 1 more hard drive internally.

- Serial ATA is much faster than older ATA/IDE interfaces.

- G4 boxes support ATA and Firewire. G5's support Serial-ATA and Firewire.

- Although it doesn't say it in the specs, The G%’s internal cdrom or superdrive (dvd) uses the older IDE or ATA interface, so there is such a port internally, but I believe it is set up to only support optical media. There's not much info on this on the apple specs pages.

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You can probably find the older IDE or ATA drives cheaper than serial ATA - but serial ATA prices are pretty reasonable as well from what I understand - certainly way less expensive than comparable SCSI drives used to be.

Also, currently serial ATA interfaces tend to be used for internal drives only - I know there are PCI cards you can buy to add more Serial ATA ports to your mac/pc but I don't think there are serial ATA external drives yet. Might be something about whether cables are shielded or something.

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www.wikipedia.org

ATA: Advanced Technology Attachment

aka IDE, ATAPI, and UDMA.

IDE: Integrated Drive Electronics

EIDE: Enhanced IDE

UDMA: Ultra Direct Memory Access

ATAPI: Advanced Technology Attachment Packet Interface

The ATA interface only worked with hard disks at first. Eventually, an extended standard came to work with a variety of other devices -- generally those using removable media. Principally, these devices include CD-ROM drives, tape drives, and large-capacity floppy drives such as the Zip drive and SuperDisk drive. The extension bears the name Advanced Technology Attachment Packet Interface (ATAPI), with the full standard now known as ATA/ATAPI.

ATA standards include ATA-1, ATA-2, ATA-3, ATA/ATAPI-4, ATA/ATAPI-5, and ATA/ATAPI-6 (not yet released, as of 2004).

www.cbacorp.com/index.htm#techtechidedrives.htm

You can integrate ATA versions within a single system. If you have more than one hard drive on a single cable, both hard drives on the cable will operate at the level of the least capable hard drive. You must ensure that you have the appropriate cable and that the motherboard supports the drive's speed.

SMART

SMART is an acronym for Self-Monitoring Analysis and Reporting Technology and is a standard for predicting the probability of hard disk failure. Western Digital first created and implemented the technology which has been integrated into the ATA standard. SMART support is a setting in the system BIOS that must me "turned on" by the user. The default setting is usually "disabled". ATA-3 drives and above use SMART.

IDE

IDE is a generic term that refers to a disk drive with a built-in controller. The controller for the drive is built in to the drive unit itself rather than on a separate board. In the early days of hard-disk technology, the hard disk and its controller were two separate pieces. With an IDE drive, however, the drive controller is part of the unit. IDE hard disks have the controller circuit board attached to the bottom of the drive.

EIDE

EIDE is an acronym for Enhanced IDE. It is not very meaningful since it can refer to ATA-2 or ATA-3 drives, or it can mean any drive conforming to the ATA-2 standard and above.

UDMA

Ultra ATA (UDMA) and Ultra DMA. These terms both refer to the same specification for improved hard-disk performance. They are the same. UDMA has four different variants: UDMA/33, UDMA/66, UDMA/100, and UDMA/133.

ATA

ATA (AT Attachment) and IDE (Integrated Device Electronics) are one and the same: a disk drive implementation that integrates the controller on the disk drive itself. This was directly connected to the I/O bus of the first PC - the IBM AT. As a consequence, the bus width is still 16 bits on all implementations.

With the introduction of Serial ATA around 2003, this configuration retroactively became renamed as Parallel ATA (P-ATA), referring to the method in which data travels over wires in this interface.

The interface only worked with hard disks at first. Eventually, an extended standard came to work with a variety of other devices -- generally those using removable media. Principally, these devices include CD-ROM drives, tape drives, and large-capacity floppy drives such as the Zip drive and SuperDisk drive. The extension bears the name Advanced Technology Attachment Packet Interface (ATAPI), with the full standard now known as ATA/ATAPI.

Until the introduction of Serial ATA, 40-pin connectors generally attached drives to a ribbon cable. Each cable has two or three connectors, one of which plugs into a controller that interfaces with the rest of the computer system. The remaining one or two connectors plug into drives. Parallel ATA cables transfer data 16 or 32 bits at a time.

For most of ATA's history, ribbon cables had 40 wires, but an 80-wire version appeared with the introduction of the Ultra DMA/66 standard. The 80-wire cable provides one ground wire to each signal wire. This reduces the effects of electromagnetic induction between neighboring wires and enables the 66 megabyte per second (MB/s) transfer rate of UDMA4. The faster UDMA5 and UDMA6 standards require 80-conductor cables. Though the number of wires doubled, the number of connector pins remains the same as on 40-conductor cables.

---> The physical connectors are identical between the two cable types. <---

If two drives attach to a single cable, the configuration generally sees one as a master and the other as a slave. The master drive generally shows up ahead of the slave drive when the computer's operating system enumerates available drives. The master drive arbitrates access to devices on the channel. Because of this, latency-sensitive devices such as early CD-RW drives often benefitted from functioning as a master, and each channel must have a master in order to function properly.

As of February 2004 no IDE hard drives exist capable of sustaining transfers at or above 50 MB/s, so these transfer limits only really affect performance when the hard drive operates in burst mode, which means that the requested data comes from its cache and the drive therefore does not have to read the data from its platters.

S-ATA (or SATA)

The SATA interface uses 7-pin cables for the data connection, and transmits the data serially rather than in parallel. In addition, Serial ATA should give users the ability to hot swap hard drives. This adds a capability that more expensive systems such as SCSI and Fibre Channel have had for a long time, though the future will tell how widely users exploit that aspect of the technology. Serial ATA also reduces the signalling voltage from the 5 volts used in P-ATA down to 0.5 volts, which reduces power consumption and electrical interference. Due to serial transfer and lower power the maximum allowable length of SATA cables exceeds that of ATA ribbon cables, which eliminates some of the problems mentioned previously.

First-generation Serial ATA interfaces have a bandwidth of 150 megabytes per second, only slightly higher than that provided by the fastest PATA mode, UDMA-133. However, while further increasing PATA bandwidth is somewhat impractical, the relative simplicity of a serial link and the use of LVDS should allow SATA to scale easily. Serial ATA II (expected to be available in 2005) will double throughput to 300 MB/s, and 600 MB/s is planned for around 2007.

The transition to Serial ATA should largely remain transparent to operating systems

Still, the need for such a high speed interface could be debated; the (rarely reached) maximum transfer rates of the fastest magnetic hard drives are currently well under 100 MB/s, and any additional bandwidth benefits only transfers from the disk's cache.

Physically, the cables used are the most noticeable change. The standard defines a seven-conductor wire with 8mm wide wafer connectors on each end as the data cable. SATA cables can be up to 1m (40 inches) long. PATA ribbon cables, in comparison, carry either 40 or 80 conductor wires and are limited to 45cm (18 inches) in length. Serial ATA drops the master/slave shared bus of PATA, giving each device a dedicated cable and dedicated bandwidth. Unlike early PATA connectors, SATA connectors are keyed Ñ it is not possible to install cable connectors upside down.

The Serial ATA standard also specifies a power connector sharply differing from the four-pin Molex connector used by PATA drives and many other computer components. Like the data cable, it is wafer based, but its wider fifteen-pin shape should prevent confusion between the two. The seemingly large number of pins are used to supply three different voltages if necessary Ñ 3.3 V, 5 V and 12 V. The same physical connections are used on 3.5 inch and 2.5 inch (notebook) hard disks.

Features allowed for by SATA but not by PATA include hot-swapping and command queueing.

To ease their transition to Serial ATA, many manufacturers have produced drives which use controllers largely identical to those on their PATA drives and include a bridge chip on the logic board. Bridged drives have a SATA connector, may include either or both kinds of power connectors, and generally perform identically to native drives. They may, however, lack support for some SATA-specific features. As of 2004, all major hard drive manufacturers produce either bridged or native SATA drives.

LVDS: Low Voltage Differential Signaling. An electrical signalling system that can run at very high speeds over cheap, twisted-pair copper cables. It was introduced in 1994

SCSI

SCSI-1

This is the original SCSI standard from 1986 and defines cabling, command sets and transfer modes. It uses an 8-bit wide bus where data transfers are done with a 5 MHz clock resulting in 5 MB/s peak transfer rate. At most 8 devices can be connected to the bus as a direct consequence of the bus width as each device is addressed using one of the 8 data lines. Most devices used on this bus are hard drives as the command set doesn't explicitly support other media in the command set.

SCSI-2

The limited transfer rate and device support forced the development of the SCSI-2 standard which was approved by ANSI in 1990. SCSI-2's greater transfer rates was accomplished by doing two things:

- Increasing the data clocking rate to 10 MHz. This is called Fast SCSI.

- Increasing the bus width to 16 bits from the original 8 bits allowed doubling the transfer rate. This is called Wide SCSI and requires different cabling compared to normal SCSI. A side effect of this is that a wide SCSI bus can use 16 devices.

Enhancements to the command set was done. This made it possible to connect devices to the SCSI bus that previously required proprietary controllers like CD-ROMs. The cable specifications had to change to support the higher data clock.

SCSI-3

The most common SCSI interface today is the parallell interface and the improvements in SCSI-3 made compared to SCSI-2 are again higher data clocking speed and better cabling to handle the higher speed. The higher speeds used on the parallell interface are named Ultra (20 MHz), Ultra2 (40 MHz) and Ultra3 (40 MHz double transition clocking).