Is there some reason as to why Hardware manufactures insist on using PIO modes? The Zorro III slots on AMIGA computers are quite capeable of using DMA transfers. Is there some limitation I have overlooked or am I correct in my assumption that it's just too costly to re-design and make another controller.
PIO modes for everyone who is not sure on what it stands for are Programmed I/O or Input/Output.
This is a technique whereby the system CPU and support hardware directly control the transfer of data between the system and the hard disk. There are several different speeds of programmed I/O None of which are all that fast mind you.
First of all, the PIO modes are defined in terms of their cycle time, representing how many nanoseconds it takes for each transfer to occur. The maximum transfer rate is the reciprocal of the cycle time, doubled because the IDE/ATA interface is two bytes (16 bits) wide. There was also talk of a "PIO mode 5", which does not really exist and was never implemented in any IDE/ATA hard disks. Apparently, at one point some discussion occurred about creating a faster PIO mode, which was tentatively called "PIO mode 5". This mode was to support a transfer rate of 22.2 MB/s, but it was never implemented (probably because the much faster 33 MB/s Ultra DMA mode 2 was on the horizon). Some motherboard manufacturers made a point of providing early support for this proposed mode in their BIOS setup programs, so you may occasionally see it mentioned.
But there you have it. Even the amazingly ancient ATA Ultra DMA mode 2 is faster than the ambiquious PIO 5 and guess what? As the name suggests, the DMA modes do not involve the CPU of your computer, they Directly Access the computers Memory DMA (Direct Memory Access)
Oh, for a comparison??
PIO Mode 4
Mode 4 -< Industry name
120 -< nano seconds (Cycle time)
16.7 -< 16.7 MB/s(Transfer rate) Dep on CPU load!
ATA-2 -< Name of mode.
This next bit could pose a potental problem on Zorro 3 because of bus width, but it's a comparison none the less and you could use other (slower) modes that still don't use the CPU.
LIKE Multiword DMA !!
Mode 2 -< Industry name
120 -< nano seconds (Cycle time)
16.7 -< 16.7 MB/s(Transfer rate)
ATA-2 -< Name of mode.
CPU independant!
Then ther's the beast
Ultra DMA 5
Mode 5 -< Industry name
40 -< nano seconds (Cycle time)
100.0 -< 100 MB/sec (Transfer rate)
ATA/ATAPI-6 -< Name of mode.
Just wondering.........