Drive speed myth

[tonymac]

Have read many posts on mixing slow drives with fast drives on same ide channel. Surely it makes no difference whatsoever? I had a single 7200 drive with a cd drive. I now have a second hard drive at 5400 on that channel set as master with 7200 as slave for capture. I get the same results. Unless the other drives are being accessed during capture, how can they possibly slow the speed of a hard drive?
I also tried disconnecting cd drive before capturing, but there was no effect at all. It has to be nonsense.

[menace]

Its actually not the physical speed of the drive that changes its the IDE access rate that is governing. For example if you have an ata100 Hard drive as master and a ata133 hard drive as slave, the slave will only run as fast as the master through the ide channel (ata100). This is why you shouldn't hook up a cdrom as master and a hard drive as a slave becasue cd-roms are notoriously slow and will in turn slow down the access rate of your hard drive.

[Nelson37]

While I essentially agree with Menace's answer, there is more to it. There are a variety of signals passing through the cable, timing and synch signals, commands, etc. Generally, keeping 2 drives on the same cable of equal performance will minimize the problem. Having both drives of IDENTICAL model is the ONLY certain way to eliminate the problem. I have seen many cases of 2 different drives on same cable, both of equal speeds, having severe performance problems or not working at all.
This is based on 15 years of PC building and repair experience.

[tonymac]

Is this not a bios problem which has been eliminated over the last few years? Data transfer at different speeds is built in these days. Some posts state that you should not have a cd drive on same ribbon as hard drive, as performance will degrade to the slowest drive on the channel. This cannot be true as your hard drive would hardly spin at all. Many computers are set up this way. Who does not have four Ide devices these days? I can understand the logic of hard drives on separate ribbons as your o.s. is always on, but provided they are both set as master I cannot see how it matters what you have as slaves

[SVCDummy]

You still don't get it! It has NOTJING to do with the speed at which the stupid motor spins the platters! It has to do with the data rate of the information on the cable.

All Buffers (i.e. the chips tied directly to the cable) of All drives connected to the IDE channel MUST respond to ANY data request on the channel before the data is considered valid and allowed to move along. Since it is a Parallel Cable - This means that even the drives with the fastest electronics (NOT MOTORS) are forced to wait for the slowest electronic response on the bus. (kind like the public school system...LOL).

CD drives have such slow motors and physical charastics that mfr.s never bothered to spend much money (until recently) on the electronic bus interface for them because the electronics will ALWAYS be waiting for the physical disk to finish it's operation.

You have to think of an IDE drive (or any other for that matter) as a 2 part system. One part physical (motor, platter, r/w heads, etc) and one part electronics (data buffers, processing chips, etc.).

It is the electronics of the drive that you have to be most concerned about!!! Because they all connect to a parallel system they can all only work as fast as the SLOWEST member.

Hope this helps. :wink:

[SVCDummy]

One last bit that may help. The data rate of IDE drives is not as much a function of the rotationl speed of the drive as it is the electronics of the drive. The electronics these days are always faster than the rotation of the platters and therefore a faster platter speed will in some ways help.

The ATA ratting is the most important! A drive rated as UDMA100 (ATA100) is faster than UDMA66 or UDMA33 (which is most CD drives now).

So, a 5400rpm ATA133 40Gb hard drive on the same cable as a 5400rpm ATA100 40Gb hard drive has just been reduced to an equal with the later drive. Yet you probably paid considerably more for the first drive.

What you were paying for was the ability of the electronics to speed data along the bus. But since the signal line on the cable from the controller will not enable responses until ALL of the DRIVES on the cable respond (regardless of whether the data is for them or not!) the faster drive is now 'waiting' for the slower one to answer the control signal even though the data is not intended for it!

This is why you don't mix drives. It also makes no difference which one you set to master or slave. The advantage of a master is that the BIOS tries to keep the masters spinning all the time and allows the slaves to spin down when not in use. This is the place where you can most directly affect the speed of the system with physical drive constraints.

Geez, and you Bio sez you're a computer techincian?!?