> I understand that ISA devices have a greater interrupt latency than PCI
> devices. Does this greater latency deteriorate overall system performance
> or just the device whose interrupts are being serviced?
ISA cards are quite a bit slower interrupting, yes. Logically, it would
slow a system down because of this, but possibly not enough for you to
detect with your eye (or whatever) unless it's a card that interrupts a
lot (like a primary use NIC for instance). Even certain ISA NICs which
send only so much data in so much time can be a problem. My old ISA NIC
had problems on this system on data xfers above 100KB (most of what I did,
tho, was less than that since it's only used for the LAN interface here (2
or 3 systems).. mainly for SMB printing, etc. My new NIC is a PCI board
(3c905B). Funny thing is, this one shows collisions (which is due to the
10BaseT hub).. only a small percentage of them though... so no prob. The
ISA NIC never showed collisions after about the first time I had the hub
installed.. I feel that collision detection/accounting was actually turned
off on the thing (which isn't right for a half-duplex interface).
Anyway... PCI cards are typically much faster than ISA, but only a few
types of cards will actually show a performance increase (I'm not talking
just NICs) due to design, drivers, or just simply because the type of card
isn't a big interrupter.
> I've got 2 10Mbps Ethernet cards, one is an ISA card and the other PCI. I
> use the ISA card as a secondary net device (eth1) which is connected to a
> cable modem. Given that the cable modem will never saturate a 10Mbps
> Ethernet card, the ISA/PCI question shouldn't be relevant to networking
> performance. I chose to use the ISA card because it leaves another PCI
> slot in my box (i686-based Linux 2.4.x) available for other uses.
How fast do cable modems run at anyway (I live in the woods.. no service
here)? I know they don't do the 1.25MB that 10Mbps NICs can do... but I'm
just curious.
> Let me add one more thing to this context. The PCI card is a 3Com 3C590
> "Vortex" so, according to the Linux doc, this device has busmastering
> capabilities. Is this a factor in overall system performance?
Again, depending on the card. NICs are always good examples because they
process a lot of data quite quickly. Busmastering, I think, is a way to
keep things in sync (or at least moving at a proportional speed) with the
CPU/RAM and whatnot.
Who knows.. my answers are prolly not exact. I've grown up with computers
over the better part of the last 15 years but times have changed, I'm
sure.
In short, it depends on the card. With a NIC.. quite possibly cause it
ties up the CPU since the CPU has to finish an interrupt before switching
to another task/process. So your run queue can get a little backed up...
but in most cases, you'd never know the difference unless you timed
everything.
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