What is UDMA (Ultra Direct Memory Access)? (Explained)

What is UDMA (Ultra Direct Memory Access)?

Ultra Direct Memory Access, or UDMA, refers to the data transfer protocol on a mass storage device, usually involving the ATA devices.

Technically speaking, according to the Ultra DMA protocol, the devices connected to the computer system are allowed to access the Random Access Memory (RAM) of the system directly without needing the Central Processing Unit (CPU).

KEY TAKEAWAYS

• The Ultra Direct Memory Access is a more advanced data transfer technology that offers higher and faster throughput than the EIDE and SCSI ranging from 16.7 MB/s to 167 MB/s at a much lower price point.
• The UDMA are quite fast methods to transfer data through the Advanced Technology Attachment (ATA) hard disk interfaces typically between the ATA devices and the computer.
• Ultra DMA is supposed to be the successor to the single/multiword DMA interface and is quite a favored choice among the users as a mode of data transfer between the ATA devices and the computer.
• There are basically eight different Ultra DMA modes ranging from 0 to 7 for Compact Flash and from 0 to 6 for the ATA devices. Each of these different modes supports different data transfer rates and timing.
• Several new computers today come with larger Ultra DMA interfaces and drives, and also allow adding an additional UDMA interface card to a current system or even to non-UDMA, older drives to expedite speed.

Understanding UDMA (Ultra Direct Memory Access)

Ultra Direct Memory Access is the specific practice of transferring data between the computer system and the devices connected to it.

UDMA is also referred to by different names, such as:

• Ultra DMA
• Ultra ATA

Ultra DMA is the data transfer protocol designed by Intel and Quantum and was introduced for the first time in 1998.

It supports the specific Advanced Technology Attachment or ATA 4 and Advanced Technology Attachment Packet Interface or ATAPI 4 standards.

However, with the release and approval of newer ATA standards later on, the Ultra DMA standards also support the following:

• ATA 5 – Ultra DMA/66
• ATA 6 – Ultra DMA/100

It is better than the earlier Direct Memory Access interface and operates twice as fast.

Though most of the computer systems today support Ultra DMA, a few may not. Typically, there are a few specific signs that indicate whether or not a computer system supports Ultra DMA or has it configured correctly. These are:

• The performance of the hard disk drives and optical drives is extremely slow.
• You are not able to use the disk-mastering software with the writeable DVD or the CD-RW.

If you find any of these issues in your computer system, then it is highly likely that the Ultra DMA feature in your system is not configured correctly.

You must also keep in mind that the hard drives with a fast UDMA mode are most commonly used on the motherboards that are designed to support slower Ultra DMA modes.

It is for this particular reason that the faster UDMA modes in most of the drives are disabled before they are shipped.

Therefore, you have to enable it before you want to use it. You can do this from the utility disk that usually comes with the drive. If you do not have it, you can follow these steps:

• Download the utility software program from the official website of the manufacturer of the driver.
• Install and run it.
• Look for UDMA support.
• Check the Enable/Disable box for your drive.

Also, check that your system has all of the requirements in order to reap the benefits offered by the Ultra DMA protocol and transfer data between the connected devices from your computer at a higher speed. Therefore check that:

• You are using the right type of cable with 80 wires and 40 pins.
• The drive is configured correctly to support the fastest UDMA speed both by the drive itself and the host adapter.
• You have selected the correct UDMA speed in the Basic Input Output System of your computer for the drive.  Preferably, it should be user-defined rather than ‘auto.’

In addition to that, you must also ensure that the host adapter, irrespective of whether it is motherboard-based or slot-based, has the Windows device drivers installed. This will help in achieving maximum performance.

If it is not, then you can check and change it by following these steps:

• Open the Device Manager.
• View the ATA/IDE host adapters.
• Check the list to find out whether the device drivers are installed.
• If the device drivers are not listed, download them from the official website of the motherboard or the system builder.
• Install and run it.
• Download and install the device drivers.

It is also very important to keep in mind that the length of the cable for Ultra DMA should be shorter in comparison to the ones used on the regular DMA interfaces.

Ideally, it should be even less than 12 inches, or 30 cm, but certainly not more than 18 inches for the systems to work fine.

For higher data transfer speeds than 66 MB/s, you should typically use a shorter and specially designed 80-wire, 40-pin cable.

This will eliminate the chances of getting a lot of Cyclic Redundancy Check or CRC errors.

What Are UDMA Speeds?

Well, it depends on the version of UDMA you are talking about. However, it is a more advanced technology in comparison to Enhanced Integrated Drive Electronics (EIDE) and Small Computer System Interface (SCSI), offering almost two to four times or higher the speed and throughput than them, ranging between 16.7 MB/s and 167 MB/s.

There are different Ultra DMA modes, each supporting different data transfer speeds, minimum cycle timings, and defining standards. For your better understanding, here are the details of each of the different UDMA modes:

• If it is UDMA mode 0, it will support a maximum data transfer speed of up to 16.7 MB/s and a minimum cycle time of 120 ns while defining the ATA 4 standard.
• If it is UDMA mode 1, it will support a maximum data transfer speed of up to 25.0 MB/s and a minimum cycle time of 80 ns while defining the ATA 4 standard.
• If it is UDMA mode 2, also known as Ultra ATA 33, it will support a maximum data transfer speed of up to 33.3 MB/s and a minimum cycle time of 60 ns while defining the ATA 4 standard.
• If it is UDMA mode 3, it will support a maximum data transfer speed of up to 44.4 MB/s and a minimum cycle time of 45 ns while defining the ATA 5 standard.
• If it is UDMA mode 4, also known as Ultra ATA 66, it will support a maximum data transfer speed of up to 66.7 MB/s and a minimum cycle time of 30 ns while defining the ATA 5 standard.
• If it is UDMA mode 5, also known as Ultra ATA 100, it will support a maximum data transfer speed of up to 100 MB/s and a minimum cycle time of 20 ns while defining the ATA 6 standard.
• If it is UDMA mode 6, also known as Ultra ATA 133, it will support a maximum data transfer speed of up to 133 MB/s and a minimum cycle time of 15 ns while defining the ATA 7 standard.
• If it is UDMA mode 7, also known as Ultra ATA 167, it will support a maximum data transfer speed of up to 167 MB/s and a minimum cycle time of 12 ns while defining the ATA Compact Flash 6.0 standard.

At this point you should also note that the Ultra DMA modes that are higher and faster than UDMA mode 2 need to lower the following aspects to transfer data smoothly:

• The time for data settling
• The impedance
• The crosstalk

This is typically achieved by using an 80-conductor, 40-pin cable for transferring data between the computer and the ATA devices.

Conclusion

The Ultra Direct Memory Access standard of data transfer allows faster moving of data over the ATA interfaces between the PC and the ATA devices.

It is much faster and offers higher output than the EIDE and SCSI and is also relatively more affordable than them. Different versions of it come with different capabilities.