PCMCIA bus specs?

[clarinathan]

Hi,

Anyone know the max transfer rate of the PCMCIA bus?

What does it connect to inside the laptop? Is it the PCI bus or what?

The laptop in question is a relatively new model which has Cardbus slots.

The reason I ask is that a friend wants to get a USB2 CDRW drive and he wants to know whether it is worth getting a usb 2 card and then connecting a cdrw drive.

Personally I can't see a CDRW drive using much of the bandwidth but if he got a HDD later how much of the 480MbitsPS would be used?

Thanks
Nathan

[geoscomp]

this will probably answer your questions concerning pcmcia transfer speeds:
http://www.quatech.com/Application_O...ver-pcmcia.htm

[confus-ed]

There are two different speeds of PCMCIA cards...

PCMCIA specification 2.1 provides for a 16-bit bus interface, has a maximum clock speed of 10MHz and is capable of speeds to 20Mbps. The 2.1 spec. does not provide for bus mastering, DMA, or multiple interrupts

In 1995 the PCMCIA 2.1 specification was enhanced to provide for 32-bit operation. The new architecture, called CardBus, was closely based on the PCI bus, and strove to provide the same improvements over the 16-bit PCMCIA card as PCI did over ISA. As such, CardBus provides for 33MHz operation and correspondingly increased data transfer. It also introduces DMA and bus mastering to PCMCIA based systems, which can markedly increase performance.

Now you'd think a USB 2.0 'type' card would be 32 bit? and you have cardbus slots, but from what I can see you are still only able to get a maximum of about 40Mbps, now I don't know of too many cdr's that exceed that speed (there are some newer ones!), but you won't have any trouble finding a hard disk that exceeds that speed.....

[clarinathan]

From what I read in the above link, surely if 10mhz give 20mbps then 33mhz will give at least 66mbps?

If this is the case then USB2 should be fine as 1394/firewire is listed as requiring 50mbps and USB2 is roughly similar in speed?

However, I may be missing the point somewhere in the conversions and the different meanings of throughput etc?!!

I realise that a CDRW drive doesn't use much bankwidth though. If my friend was using a HDD then clearly that would need a fast connection.

[geoscomp]

I think you are correct in your assumptions..most external cd-rw drives are limited in their burn speed anyway..just make sure you have one with buffer underrun protection, which most have, and you should be ok..

[confus-ed]

2 x20 =40

But when I think about it none of the answers are right.....

A PCMCIA card can go as fast as the PCI bus its bridging to....

Cardbus Controllers & Windows

CardBus host controllers are a type of PCI-to-PCI bridge. A PCI-to-PCI bridge connects two PCI buses, increasing expansion capability beyond the limitations of a single bus

[clarinathan]

Hmmmmm,

I see your point!

Does anyone have a clear explaination of the different speeds and factors involved.

For example, am I correct in thinking that the PCI bus generally runs at 33mhz?

What effect does this have on the amount of data it can carry?

Also what about the Mbits per secs or Mbytes per second thing?

What exactly does 480 Mbps mean?

[confus-ed]

PCI bus generally is 33MHz.

Here's something about bus speeds & bandwidth & well..... loads of tosh!

PCI bus bandwidth or 127.2 MBytes/second (or 133 depending on how you do the math...)

8 bits = 1byte

480 Mbps = 60MB/s

I'm tired now.....