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What is this.......?


Section 7-0: What is this......?
  1. FYI
  2. ATA / ATAPI-5
  3. Why not CD/RW and Hard drive on same Channel
  4. A word about SCSI and  IDE
  5. A brief History on ATA interface, Transfer Modes and Speeds
  6. What is Ultra3 SCSI and some of its advantages?
  7. What is the new Ultra2 SCSI specification? (990427-0014)
  8. What is Firmware?
  9. What is ATAPI?
  10. What is UDF?
  11. What is Packet Writing?
  12. What is NVRAM and ESCD?
  13. What is the speed of CD-R & CD-RW media?
Some basic background information




7-0-1: FYI

The Integrated Drive Electronics ( IDE ) is the primary interface used to connect a hard disk drive to a PC and refers to the fact that the interface electronics or controller is built into the drives themselves, these include CD-ROM, DVD, CD/RW, high-capacity floppy and tape drives. The IDE connector on motherboards in many systems is nothing more than a stripped down bus slot. In ATA IDE installations, these connectors normally contain a 40-pin subset of the 98 pins that would be available in a standard 16-bit ISA bus slot.

7-0-2: ATA / ATAPI-5

Copies of any of the published standards can be purchased from ANSI or Global Engineering Documents. ATA-5 includes ultra-ATA/66, which doubles the ultra-ATA burst transfer rate by reducing set-up times and increasing the clock rate. The faster clock rate increases interference, which causes problems with the standard 40-pin cable. To eliminate noise and interference, a new 40-pin, 80-conductor cable was developed. This cable was first announced in ATA-4, but now is mandatory in ATA-5 to support the ultra-ATA/66 mode. This cable adds 40 additional ground lines between each of the original 40 ground and signal lines, which help shield the signals from interference. This cable will work with older non-ultra-ATA devices as well. The new cable will support the Cable Select feature and have color coded connectors. The blue end connector should be connected to the ATA host interface (usually the motherboard). The black opposite end connector is known as the Master position, which is where the primary drive will plug in. The gray middle connector is for the Slave position.

7-0-3: Why not CD/RW and Hard drive on same Channel

When only one drive is installed, the controller responds to all commands from the system. When two drives and therefore two controllers are installed all commands from the system are received by both controllers. Each controller then must be set up to respond only to commands for itself, thus Master / Slave. Most CD-ROM, Tape Drives, DVD and CD/RW run at lower IDE mode speeds, this would force your hard disk to run slower if they shared a single cable. IDE does not normally support overlapping access such as SCSI, basically, when one drive is running the other can not be accessed. By keeping them on separate channels, you can more effectively overlap accessing between them. This is why in a system with 4 devices, that includes a Zip drive, the Zip is connected to Pri IDE as slave, it can not support the transfer rate and should never be in use while the CD/RW is in the "burn" process.


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7-0-4: A word about SCSI and IDE: ( author; VinTek )

A couple of years ago, I would have told you to make sure that your CD-ROM and CD-RW drives were on separate channels. This was because EIDE drives were notoriously unreliable in managing I/O tasks on the same channel. You would get buffer underruns and the result would be a coaster. Recently, however, CD-RW drives have improved to the degree (through larger buffers and other such improvements) that many people, including myself, routinely install both drives on the secondary channel.

However, you still have EIDE drives, which in turn means that your CPU is handling the I/O chores. CD-RW drives have improved to the point where buffer underruns are much less frequent than they used to be, but you'll still risk a coaster if you try to do too much while burning a CD. The load on the CPU would distract it from the burn, and boom! Buffer underrun. That is why most of us recommend that you turn off all unrelated programs, such as antivirus utilities and screensavers, while burning a CD. I go the extra mile by creating a fixed swap drive so that Windows does not try to resize it during the burn.

This brings us to SCSI. Because of the improvement in IDE drives, SCSI doesn't hold as much of an advantage as it used to, but it's still the closest you can get to having bulletproof burns. This is because the SCSI controller chip takes over the job of managing the I/O tasks from the CPU. I have seen SCSI systems complete a burn through to disk finalization even after a BSOD! That is impressive. With a good SCSI card, you can daisy chain up to 27 devices (cheaper ones max out at about 7). Drawbacks are expense (both in terms of the card and the peripheral) and complexity. There is the bother of having to set the SCSI ID and terminate the last device in the chain. In addition, naturally, if you truly want a bulletproof burn, then both your source and target should be SCSI. This means having to have a SCSI hard drive and SCSI CD-ROM/DVD player.

Is SCSI worth it? If you burn a lot of CDs (maybe you have to back up and archive databases on a regular basis; maybe you're a music fiend and want to custom-mix a lot of audio CDs), then yes, the added reliability is probably worth the money. If you are like most people who just want to back up files and occasionally want to mix a CD for your car, then stick with EIDE.

A word about USB. They are pretty neat. At this point, I have seen them go up to 4X, meaning that you can burn a CD in about 19 minutes. This is in contrast to 8X drives, which will take about 10.5 minutes. There are some 12X drives around, but I have not had any experience with them. Those are CD-R times, by the way. CD-RW times are often, but not always, twice the CD-R times. What you gain is the fact that you do not take up any extra IRQs and you also get portability.

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7-0-5: A brief History on ATA interface, Transfer Modes and Speeds

ATA was original created in form for small-capacity low-cost drives. It has evolved long with the needs of modern PC, higher capacities and faster access times. The standard hard drives in most PC`s use the ATA Attachment interface and now most new CD-ROM / CD-RW drives also use one of the more recent versions of ATA. What makes ATA so appealing is its simplicity, connecting them require only two cables, a signal cable and a power cable. You do not have to worry about RLL data coding, modulation techniques or proper termination.

Around the time Seagate developed Fast ATA, Western Digital sought to strengthen the original ATA standard, Enhanced IDE / EIDE. Later the two groups united, standardization of ATA was developed and approved. All aspects of both Fast ATA and EIDE are now part of the official standard. In 1996 ATA-2 standard, faster transfers became officially sanctioned. In 1998 the packet interface that extended official ATA support to CD / CD-RW drives and other devices was added under ATA-4.

The information available is extensive, but ordinarily you need only be concerned with modes and transfer rates when you are selecting a hard disk drive to match with your PC. In operation your PC`s BIOS will automatically recognize the device and set itself up for the fastest operating mode that it shares with your hard disk drive. Below is a chart showing relevant  Transfer modes and Speeds.

Transfer Mode Cycle time in Nanoseconds Speed in MBps Standard
PIO Mode 0 600 1.67 ATA
PIO Mode 1 383 2.61 ATA
PIO Mode 2 240 4.17 ATA
PIO Mode 3 180 11.1 ATA-2
PIO Mode 4 120 16.7 ATA-3
PIO Mode 5 90 22  
Ultra DMA Mode 0 235 16 ATA-4
Ultra DMA Mode 1 160 24 ATA-4
Ultra DMA Mode 2 120 33.3 ATA-4
Ultra DMA Mode 3 90 45 ATA-4
Ultra DMA Mode 4 60 66.6 ATA-5
Ultra DMA Mode 5 40 100 ATA-6


Max Transfer Modes PIO 1 PIO 4
Max Transfer Rate 4
Max Connections 2 2 2 2 per cable 2 per cable 2 per cable
Cable Required 40-pin 40-pin 40-pin 40-pin 40-pin, 80-conductor 40-pin, 80-conductor
Additional Features - Base - Speed
- Synchronous Transfers
- S.M.A.R.T.
- Secure Mode
- Queuing
- Overlap
- Speed
- Data Reliability
- Speed
- Data Reliability

-LBA addressing extended to 48-bit number

-Maximum drive capacity 144.12 PB (Petabytes=quadrillion bytes)

Year Introduced 1981 1994 1996 1997 1999 2001


ATA/ATAPI-6 is ANSI NCITS project number 1410.

In early 2001 ATA/ATAPI-6 is about to be completed. ATA/ATAPI-6 include another even faster Ultra DMA mode, Ultra DMA 100. It also includes a method of increasing the number of LBA bits from 28 to 48 and increasing the Sector Count from 8 bits to 16 bits.

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7-0-6: What is Ultra3 SCSI and some of its advantages?

What is Ultra3 SCSI?

Ultra3 SCSI is the next generation of SCSI development. Ultra3 SCSI allows for bandwidth of 160 Mbytes/sec. This is done by doubling the number of data signals sent per clock cycle compared to Ultra2 SCSI.

Why is that speed necessary?

As applications and data become larger, the demands on servers also increase. To be able to retrieve data and send it to users efficiently, requires faster hard drive access with lower CPU utilization. Just three Ultra2 SCSI drives can saturate an Ultra2 SCSI channel, leaving no bandwidth for other SCSI devices. With Ultra3 SCSI, there is enough bandwidth for future expansion without loss of performance.

Will I be able to use my older SCSI drives with an Ultra3 SCSI drive?

Ultra3 SCSI maintains full backwards compatibility with legacy SCSI devices. Since Ultra3 SCSI is a modified Ultra2 SCSI solution, it uses Ultra2 SCSI cables, insuring ease of installation.

What is the maximum cable length?

With the use of LVD (low voltage differential) technology, Ultra3 SCSI provides for cable lengths of up to 12 meters, allowing for multiple drive configurations and hassle-free external device setup. In a single-device channel, cable length can actually be 25 meters.

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7-0-7: What is the new Ultra2 SCSI specification? (Article #990427-0014)

This information describes the new features of the Ultra2 SCSI specification.

This information applies to the following product(s):
- 2940U2W series, 2930U2 series, 3950U2 series

This information applies to the following Operating System(s):
All / PC
Mac OS (PowerDomain)

Ultra2 SCSI is a subset of the SCSI-2 specification. Ultra2 / LVD (Low Voltage Differential) is less susceptible to noise and has reduced power consumption comparted to the previous SCSI standards which used either SE (Single Ended) and HVD (High Voltage Differential) as their mode of termination. Ultra2 SCSI adapters support Ultra2 / LVD devices with a SCSI burst transfer speed of up to 80MB per second. Maximum cable length is as follows:

- 25 meters (74.5 ft) point-to-point - an Ultra2 SCSI controller connected to a single Ultra2 LVD device

- 12 meters (36 ft) total - an Ultra2 SCSI controller connected to 2 or more Ultra2 LVD devices

LVD (Low Voltage Differential) transceivers which feature low power consumption, are less susceptible to noise and have reduced power consumption, allows the transceivers to be designed into the CMOS of the SCSI chip.

LVD will allow 16 bit wide transfers speeds of up to 80MB/sec. With point-to-point (one SCSI device and host adapter) cable length of 25 meters and multi device maximum cable length of 12 meters (36 ft). The voltage swing of the LVD interface chip is from .7 to 1.8 volts DC.

Multi-mode chips allow either single ended or LVD devices to be connected to the bus. If LVD devices are connected and then a single ended device added, the bus will switch automatically to a single ended mode, with the limitations of speed (40Mb/s) and cable length (3m) of the single ended SCSI, limiting or disabling the LVD devices.

Although the bus will handle both single ended and LVD devices in a mixed environment, the devices should be kept separated. Having only LVD devices on the LVD segment and Single ended devices on the SE segment and not mixed.


The two Types of Interfaces defined for SCSI are, a Differential Interface and a Single-Ended Interface. The electrical interfaces are the means by which the Data Bus Signals and Control Signals are transmitted and received by SCSI devices.

There are two styles Differential Communication:

A Differential Interface is defined as a reference to a type of circuit that makes use of the difference between two signals (a + Signal line and a – signal line).

Low Voltage Differential Interface:
LVD (Low Voltage Differential), such as the AHA-2930U2, AHA-2940U2W and
AHA-3950U2The voltage swing of the LVD interface is from .7 to 1.8 volts DC.

High Voltage Differential Interface:
HVD (High Voltage Differential), such as in the AHA-1744 and/or AHA-2944UW, overcomes cable limitation with high powered differential drivers/receivers, but this requires additional power consumption (the voltage swing of HVD is .8 to 5.25 Volts DC) and circuits. HVD is a very proprietary style interface and cannot be mixed with either Single Ended or LVD style devices. Adaptec HVD controllers only support HVD style devices.

Single-Ended Interface:
A Single-Ended Interface is defined as the difference between one signal and some reference voltage (or ground).

SE (Single-Ended), such as the AHA-1540 series and AHA-2940 Series controllers, transmits signals, using a signal line paired with a Ground return line.

Product: SCSI Hardware Sub-Product: Unspecified Date Created: 04/27/1999 09:13 AM Article #: 990427-0014
Category: General Date Updated: 08/25/1999 02:06 PM    


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7-0-8: What is Firmware?

What is firmware?
Firmware is a special-purpose module of low-level (e.g., hexadecimal, machine code) software that serves two purposes. First, it acts like a BIOS, enabling the device to take stock of its capabilities and to render those capabilities functional. Second, it coordinates the activities of the hardware during normal operation and contains programming constructs used to perform those operations. For example, in a typical modem, the firmware will be a factor in establishing the modem's data rate, command set recognition, and special feature implementation.

Firmware is stored in a special type of memory chip that doesn't lose its storage capabilities when power is removed or lost. This non-volatile memory is classified as "read-only" memory (ROM) because the user, during normal operation, cannot change the information stored there. The basic type of chip is called a PROM, which is programmable by any technician who has a programming console. A basic PROM receives one version of firmware. That code is "burned in" to the PROM and cannot be changed. To update the firmware, the PROM must be physically removed from the device and replaced with a new chip.

Flash Capabilities
Improvements on this technology have rendered EPROM, PEROM, and EEPROM chips, which are variations of the PROM that are erasable using either UV-light (e.g., the origin of the term "flashable") or electrical energy.

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7-0-9: What is ATAPI?

The ATA Packet Interface (ATAPI) is an extension of the ATA (IDE) interface designed to allow devices other than Hard-drives to plug into an ordinary ATA (IDE) port. Hard-drives have ATA (IDE) support through BIOS, ATAPI devices require a device driver to support them. Booting from a ATAPI CD-ROM is only possible with an EL Torito CD-ROM and the latest motherboard BIOS versions.

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7-0-10: What is UDF?

UDF is a file system (Universal Disk Format file system).   Similar to the other file systems commonly seen on PCs such as CDFS, NTFS and FAT.  UDF is the specified file system for a number of formats.   For example, it is the file system for DVD-Video, DVD-Audio, and SACD - none of which have anything to do with packet writing.  One of the formats that the UDF file system is specified for is packet writing on recordable optical media (Orange Book III).


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7-0-11: What is Packet Writing?

Packet writing is a technique for writing small 'chunks' of data to an optical disk.  Because of the limitations of the original optical recorders, data was written to optical disks in fairly large 'chunks' (minimum 300 blocks- about 600 KB - with another 150 blocks of overhead for each 'chunk' ).  If the actual data to be written was less than 300 blocks (as it often was), the physical burn was padded out with zeros - a waste of space.  And that 150 blocks of overhead was pretty wasteful as well.     As the equipment got better, there was really no reason to continue to write data in such large (and wasteful) chunks. Thus, packet writing.

Just for comparison, the fixed length packet size as used on CD-RW is 32 K.

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7-0-12: What is NVRAM and ESCD?

ESCD is an acronym for Extended System Configuration Data, a format for storing information about Plug-and-Play devices in the BIOS. Windows and the BIOS access the ESCD area each time you reboot your computer. This memory is also referred to as NVRAM.

NVRAM is an acronym for Non-Volatile Random Access Memory, a type of memory that retains its contents when power is turned off. One type of NVRAM is SRAM (Static Random Access Memory) that is made non-volatile by connecting it to a constant power source such as a battery. Another type of NVRAM uses EEPROM chips to save its contents when power is turned off. In this case, NVRAM is composed of a combination of SRAM and EEPROM chips.

The NVRAM chip is actually manufactured in layers and each layer can be made of a different substance so that it performs different functions. In a Dell computer, NVRAM contains the BIOS (Basic Input/Output System), a CMOS layer (complimentary metal-oxide semiconductor), and several other layers.

Prior to shipping systems with a flashable BIOS chip, you were required to remove the BIOS chip from the motherboard in order to change BIOS. These systems used either a PROM or EPROM (Programmable Read-Only Memory or Erasable Programmable Read-Only Memory) chip. The difference between the two being that the PROM could not be rewritten while the EPROM could be erased by removing the sticker from the top of the chip and shining a high intensity UV light into the window on the top. EEPROMs were then developed. These are Electrically Erasable Programmable Read Only Memory. EEPROMs can be erased with an electrical signal. These are the physical chips used for most flash BIOS chips.

All Dell systems now ship with a flashable BIOS. This means that you can upgrade the system BIOS without removing the chip from the motherboard. All you have to do is download the flash program from Dell systems use a NVRAM chip to hold the BIOS and System Setup information.


For more information on how to download and flash the latest BIOS for your system, refer to Dell Knowledge Base Article: FA1033387 “How can I obtain the latest upgrade to my basic input/output system (BIOS) or system setup file?”

Clearing the NVRAM on a PnP system can correct a multitude of problems, ranging from modems that will not configure to a hard drive not recognized by the system. Depending on system type, NVRAM is either cleared by a motherboard jumper, by using a selection in the system setup program to reset configuration data, or a keystroke combination while the system is booted to its setup program and has all keyboard lights lit. For example, most Dimension systems, other than the more recent models, are good examples of systems that required a motherboard jumper to be moved in order to clear NVRAM. Most OptiPlex systems use the keystroke method.

For help with specifics on your Dell system, or additional troubleshooting support, search the Support Your Dell section on the Dell Web site at Dell provides you with the troubleshooting tools necessary to resolve most any problem.

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7-0-13: What is the speed of CD-R & CD-RW media?

From time to time we get a number of questions asking about the "speed" of CD-R & CD-RW media, exactly what does this mean and what speed do I need / should use. One of our Regulars, ctalia4000 ~ Carolyn, provided a link that does a very good job of covering the issue and the link has additional material as well. Take a moment browse it for yourself:

I want to thank Carolyn for the link,


Best Regards,

Jeff  ~ Predator


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