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part FAQ part QUESTION (long)

Tags:
  • Hard Drives
  • UDMA
  • DMA
  • Storage
Last response: in Storage
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Anonymous
a b G Storage
March 13, 2001 8:21:25 AM

As a result of my recent harddrive calamities, I've been doing some research/review. Thought I'd post the findings as a sort of mini FAQ, and also pose this question:

What's the relationship between EIDE, ATA, PIO, DMA, UDMA?

I'm particularly confused about DMA v. UDMA, and why it is that win98 gives you the option of enabling DMA for a harddrive when UDMA is supposed to be 'automatic,' i.e., something between the chipset and the hd, nothing to do with the OS. Also, does UDMA override/replace PIO? If you enable PIO 4 in the BIOS, does that override UDMA? For the specifics of my trouble, you can read "DMA-high bench, terrible perfomance" if you haven't already.

I got most of the information below from www.maxtor.com in the glossary section of their support pages.

-hawkeye


maxtor:

BUS
A collection of functionally parallel conductors that forms an interconnection between functional blocks in a digital device. A length of parallel conductors that forms a major interconnection route between the computer system CPU (central processing unit) and its peripheral subsystems. Depending on its design, a bus may carry data, addresses, power, and more.


from maxtor udma faq:

Q04: Are there any special system or software requirements to use an Ultra DMA drive?
A04: Yes as follows:

4. Windows 95B and Windows 98 have LIMITED driver support, however Operating Systems (OS) do not normally include the UDMA drivers, as the OS does not have any direct control over this operation. If the motherboard provides the chip sets and the drivers are installed, after the OS, then the system will automatically utilize the maximum data transfer rate possible when transferring data between RAM and the hard drive.


maxtor:

DIRECT MEMORY ACCESS
A means of data transfer between the device and host memory without processor intervention. There are two DMA modes, Single and Multi-Word. Since single word is slower than PIO mode, no one uses it. It will be ignore it here. Multi Word DMA is used in EISA, VLB, and PCI equipped systems. They are capable of the very fast transfer rates, utilizing cycle times of 480ns or faster. The current ATA specification limit is 150ns. This flowchart show the virtual elimination of the CPU from the transfer process.

model

harddisk <---> memory


microsoft:
DMA (also referred to as bus mastering) reduces CPU overhead by providing a mechanism for data transfers that do not require monitoring by the CPU. The transfer rate for a particular data transfer event will not noticeably increase. However, overall CPU overhead should be reduced using DMA mode.


maxtor:

PIO
Programmable Input Output. A means of accessing device registers. Also describes one form of data transfers. PIO data transfers are performed by the host processor using PIO register accesses to the data register.

model

harddisk <---> cpu <---> memory

This is a quick and efficient way to transfer data, but it ties up the CPU a lot.

PIO Multiple Mode - (AKA: Multi-Block Mode or just Block Mode)
Multiple mode transfers are handled similarly to a standard PIO data transfer. The only difference is how often the drive issues interrupts. In standard PIO, each sector (512 bytes) of data transferred, requires one interrupt. With Multiple Mode, we can transfer 2, 4, 8, 16 or more sectors with each interrupt. For instance, if multiple mode is set to 4, each interrupt indicates the drive is ready for 4 sectors of data (read), or has completed the transfer of 4 sectors of data (write). The advantage is that we eliminate some of the system overhead involved in a PIO transfer,


PIO Mode
Mode Cycle Times Transfer Rate
0 600ns 3.33MB/s
1 383ns 5.22MB/s
2 240ns 8.33MB/s
3 180ns 11.11MB/s
4 150ns 16.66MB/s

Single Word DMA
Mode Cycle Times Transfer Rate
0 960ns 2.80MB/s
1 480ns 260MB/s
2 260ns 8.33MB/s

Multi-Word DMA
Mode Cycle Times Transfer Rate
0 480ns 4.16MB/s
1 150ns 13.33MB/s
2 60ns 16.66MB/s


maxtor:

ULTRA DIRECT MEMORY ACCESS (ULTRA-DMA)
The latest improvement of the EIDE device interface. Also known as ATA/ATAPI-4, Ultra-ATA, or Ultra-DMA/33, this is the latest advancement to the ATA specifications (draft): ATA/ATAPI-4. Which, among other improvements, supports Ultra DMA. This interface has a theoretical maximum data transfer rate (burst, not sustained) of 33MB/sec.

Ultra-DMA doubles the maximum transfer speed of the ATA-3 standard. Compare the Ultra DMA maximum burst transfer rates with the old ATA standards above.


ATA-4 Extensions Synchronous DMA Mode for Ultra DMA/33
Mode Cycle Times Transfer Rate
0 235ns 16MB/s
1 160ns 24MB/s
2 120ns 33MB/s

As you can see, Ultra DMA/33 achieves nearly double the transfer rate of the existing ATA interface while not increasing the cycle time of the ATA bus clock over the rate currently used for PIO Mode 4.

This apparent miracle is achieved by:

Improving _timing windows_ in the protocol on the ATA bus;
Reducing propagation delays by pipelining data transfers;
Transferring data in synchronous (strobed) mode;

In addition, Ultra DMA/33 improves data integrity by using a Cyclic Redundancy Check (CRC) to flag any data transfer errors that may be made over the ATA bus (Note: In this application CRC is only used to improve data integrity for ATA bus transfers, it is not used to improve the data integrity of either disk drives or host systems).

Ultra DMA/33 requires no physical change to the cable, receivers, or drivers of the ATA bus. Furthermore, Ultra DMA/33 protocol and commands have been designed to be compatible with existing ATA devices and systems. Thus, new Ultra DMA/33 devices will be backwards compatible with most older (non Ultra DMA/33) systems. Older ATA-1/2/3 devices will also be forwards compatible with systems that have Ultra DMA/33 capability.


Q01: What is Ultra DMA?
A01: Ultra DMA (UDMA) is the latest advancement to the ANSI ATA specifications. For detailed information about the ANSI ATA specifications view them at the T13 Committee site at http://www.t13.org/. ATA-4, among other improvements, supports Ultra DMA modes 0, 1 and 2. UDMA mode 2 supports burst data transfer rates up to 33 MB per second (MB/s). ATA-5, among other improvements, supports Ultra DMA modes 3 and 4. UDMA mode 4 supports burst data transfer rates up to 66 MB/s.

ATA-5 Extensions Synchronous DMA Mode for Ultra DMA
Mode Cycle Times Transfer Rate (Burst)
0 120 ns 16.6 MB/s
1 80 ns 25 MB/s
2 60 ns 33.3 MB/s
3 45 ns 44.4 MB/s
4 30 ns 66.6 MB/s

note: 0 is equivalent to PIO mode 4 (ATA-3)


UDMA/33 (ATA-4) doubles and UDMA/66 (ATA-5) quadruples the maximum transfer speed of the ATA-3 interface while maintaining the cycle time of the ATA bus clock at the rate used by PIO Mode 4.

This apparent miracle is achieved by:

Having the entity transmitting the data, either host or device, provide the clocking signal for the data
Using both edges of the clocking signal to strobe the data
For modes 3 and 4, improving the cable connecting the devices to the host.



AT ATTACHMENT (ATA) (Advanced Technology Attachment)
The ATA Interface is the dominant storage interface for personal computers. ATA was originally defined as a standard for embedded fixed disk storage on IBM AT compatible personal computers. AT stands for "Advanced Technology", which refers primarily to it's then "revolutionary" 16-bit bus. In recent years ATA-3 and ATA-4 have enhanced the functionality of the ATA interface to increase performance and interface a wider range of personal computer storage devices.



ATA Standards: Defines the physical, electrical, transport, and command protocols for the internal attachment of storage devices.

ATA-1: A device which complies with the ANSI X3.221-1994 "AT™ Attachment" Interface for Disk Drives - commonly known as IDE.

ATA-3: A device which complies with the ANSI X3.298-1997, "AT™ Attachment-3" Interface for Disk Drives - also known as Fast ATA or EIDE.

ATAPI: "AT™ Attachment Packet Interface" is an extension to the ATA protocol which defines a packet protocol for devices such as CD-ROM and Tape devices. The ATAPI protocol allows these devices to share the ATA bus with traditional ATA disk drives.

ATA/ATAPI-4: "AT™ Attachment with Packet Interface" is the combined ATA-4 and ATAPI protocol document. Complies with the ANSI X3T13/D96153 - also known as Ultra ATA or Ultra DMA. This is the version that supports up to 33MB/sec data transfers (in burst mode).

ATA/ATAPI-5: "AT™ Attachment with Packet Interface" is the latest protocol proposal. This is the version that will support up to 66MB/sec data transfers (in burst mode). Enhances data integrity and reliability through internal data checking and correction algorithms. Also includes a new UDMA "Ground Bus" 80-wire cable requirement.



Q01: What is IDE/ATA?
A01: Integrated Drive Electronics (IDE) is a generic term applied to any drive with an integrated (built-in) disk controller. The first drives with integrated controller were Hardcards. In the IDE architecture, the disk controller is integrated into the drive. This combination drive/controller assembly usually plugs into an interface on the motherboard or an interface card plugged into an empty bus slot. The ATA Specification is simply a set of rules or guidelines that an IDE drive should conform to.
NOTE: The current revision of the ATA specification is ATA-5.
Return to Questions Return to Main FAQ Page


Q02: What does the IDE interface actually do?
A02: The primary job of the IDE interface is to transmit/receive data to and from the drive.



Q04: What is Enhanced-IDE (EIDE) and Fast-ATA?
A04: Enhanced IDE (EIDE) was a marketing program first initiated by Western Digital. EIDE has two sides:
Software - the Enhanced BIOS Specification that surpasses the 504 MB hard drive capacity limitation
Hardware - hard drives that conform to the ATA-2 and ATA-PI Standards
Fast-ATA, EIDE's counterpart, was a separate marketing program that was introduced by Seagate and Quantum. This program leaned conservatively toward the ATA-2 specification.
Return to Questions Return to Main FAQ Page


Q05: What are the main features of EIDE
A05: These are the main features:
Faster transfer modes- PIO modes 3-4, DMA mode 2 and UDMA.
Multiple Read/Write commands
LBA mode, translation for drives larger than 504 MB
Four devices on the ATA controller (secondary port)
CD ROM and Tape Drive support



Never cut what you can untie. -Joubert (1754-1824)<P ID="edit"><FONT SIZE=-1><EM>Edited by haughki on 03/13/01 05:24 AM.</EM></FONT></P>

More about : part faq part question long

Anonymous
a b G Storage
March 14, 2001 2:38:14 AM

>>What's the relationship between EIDE, ATA, PIO, DMA, UDMA?<<

ATA is a standard. Repeat that to yourself.. ATA is a standard. EIDE was a subset feature of the ATA-2 standard, I believe it was ATA-2 anyways.

PIO, DMA, UDMA are transfer modes. New ATA standards have generally defined faster and/or larger bandwidth capable transfer modes.

>>I'm particularly confused about DMA v. UDMA<<

DMA is DMA.. Ultra DMA is just a new extension of DMA tranfer modes from single..to multiword.. to Ultra DMA.

>>and why it is that win98 gives you the option of enabling DMA for a harddrive when UDMA is supposed to be 'automatic,' i.e., something between the chipset and the hd, nothing to do with the OS.<<

The maxtor faq answers this. ". If the motherboard provides the chip sets and the drivers are installed, after the OS, then the system will automatically utilize the maximum data transfer rate possible when transferring data between RAM and the hard drive." Any piece of hardware that you want the OS to use must have drivers. So the above means that if you want applications and Windows to use the UDMA capabilities of your chipset, you must have drivers that tell it how to do that, which means Bus Mastering drivers for integrated controllers. Obviously ATA controllers (for UDMA capable drives) and SCSI controllers automatically use DMA when drivers for those devices are installed.

>>Also, does UDMA override/replace PIO? If you enable PIO 4 in the BIOS, does that override UDMA? For the specifics of my trouble, you can read "DMA-high bench, terrible perfomance" if you haven't already.<<

Your bios settings in this area will override anything you can do in the OS.





***check the jumpers 1st then check em again***
March 16, 2001 2:42:09 AM

----------------------------
Your bios settings in this area will override anything you can do in the OS.
----------------------------

Actually I once had a drive accidentally disbaled in BIOS (well, interface set to none) and WIN2K still discovered it and ran it (badly). It managed to get 3MBs transfer (UATA100) if you turned off drive caching.

That one had me really confused for a while - thought it was a dud drive... :o ) I never cease to amaze myself about how stupic I can be at times...

-Your Comany Names Could Be Here-
e-mail for application details.
!