Dard Drives

What is the difference between an Ultra ATA and an Ultra DMA Hard Drive?
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ATA is the same as IDE.
Have not heard of ultra dma for a hard drive,  maybe ultra scsi.
You have Ultra DMA/33 and Ultra DMA/66.  DMA stand for the way the disks communicate with the controller.  Before the DMA (Direct Memory Access) you had the PIO modes (Programmed Input Output).  The 33 (66) stands for the maximum throughput of the bus (33 or 66 MB per seconds).  In most cases 33 is enough because the disks theirself aren't capable of transfering that amount of data.

Ultra ATA is the same as Ultra DMA.  Different names are used by the manufacturers.

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ATA: Known also as IDE, supports one or two hard drives, a 16-bit interface and PIO modes 0, 1 and 2.
ATA-2: Supports faster PIO modes (3 and 4) and multiword DMA modes (1 and 2). Also supports logical block addressing (LBA) and block transfers. ATA-2 is marketed as Fast ATA and Enhanced IDE (EIDE).
ATA-3: Minor revision to ATA-2.
Ultra-ATA: Also called Ultra-DMA, ATA-33, and DMA-33, supports multiword DMA mode 3 running at 33 MBps.
ATA/66: A new version of ATA proposed by Quantum Corporation, and supported by Intel, that will double ATA's throughput to 66 MBps.
two letters:  D & M
good answer ray, that pretty well explains it.

One point that is worth mentioning - for MOST applications, access time is a LOT more important than data transfer rate.  As Davy points out, you rarely can actually use the transfer rate of even the slowest drive.

The exception is if you are doing a lot with very large, unstructured files.  For example, if you're doing a lot of photo work with very high resolution images (say greater than a megabyte per file).  This doesn't apply to structured files like databases where access time is the metric that matters.

As the drive gets larger, access time matters more.  In general, for multiuser operating systems (unix, VMS) access time matters more.  In general, for operating systems that require very large memory (NT, VMS) transfer rate can be useful. Non vitrual memory operating systems (DOS) will have program load times improved by transfer rate (but not virtual memory OSs like Windows or OS/2 which don't load programs but rather fault them in).

For 'normal' use, i.e. Windows 9x with a mix of files, the only place you will see the effect of transfer rate is when you are making backups, and even there, depending on the backup software, it may not matter much.
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