PCI mostly just works. Also, PCI mainboards almost always have the controller integrated. Also, there are a lot of choices regarding PCI cards - USB, SATA, you name it.

VLB is much more problematic. Not every controller card works in every system. Practically only controller and video cards exist. Cards are long.

So, practically speaking, PCI is much better. Though I think there's something cool about a 486 with VLB that a PCI system can't replicate.

386SX wrote:

Hi,

I'd like to know your opinion on the differences technically and on the real results of the difference between these bus. Were PCI "that" better or just another commercial choice?

Bye

Closest thing I can give you for "real tests" is DX4-100 with VLB ET4000/W32p on UMC chipset (MB8433) vs DX4-100 with PCI ET4000/W32p on UMC chipset (MB1433).

VLB was tied to the 486 archtecture, so it was much harder to implement on newer systems. PCI wasn't tied to any specific processor.

But considering the speed connection beetween the card and the cpu, was PCI more advanced or just a more compact solution to the same capabilities of the VLB? Considering the VLB was built to solve ISA bottleneck...

VLB was horrid. Its minimal advantages are that it's cheaper to design a VLB motherboard, and that it also doubles as an ISA slot.

Everything else about it is just wrong - the cards are a pain to fit, they're too long, they don't work reliably in systems with >33MHz bus, there's no plug and play and it won't work in anything except a 486 based x86 PC.

VLB cards tend to be more low profile than PCI, as they must have more surface area due to their length.

Initial 486 PCs with PCI were somewhat more expensive and had their quirks, but at least they heralded a proper expansion bus. My 486 computer supplier was a long holdout on VLB, but basically it was only for self interest and cost. It was very clear in the early 90s that VLB did not have a future, but a couple of hundred extra quid for PCI support was non trivial.

But considering it was a 486-only bus, should it be considered closer to its hardware and then in someway faster? Or just the fact better pci version of gpu was coming out make it just obsolete? I know that from a logistic point of view they were painfull to mount and unmount but I always liked the idea that for a 486 built it has more sense.

Speed will be more dependent on the card I suspect.

VLB didn't even make sense for 486s, because the DX50 and third party 40MHz CPUs broke VLB, as VLB is not de-coupled from the processor frequency. It was only ever a stopgap in the early days, when 486 frequencies were 33MHz or below.

It was a useful improvement over ISA disk controllers, and I have a soft spot for my Cirrus Logic 5426 VLB card, but that's not really because it's VLB.

ynari wrote:

VLB didn't even make sense for 486s, because the DX50 and third party 40MHz CPUs broke VLB, as VLB is not de-coupled from the processor frequency. It was only ever a stopgap in the early days, when 486 frequencies were 33MHz or below.

Not necessarily. I have a 486DX2-80 which runs just fine with VLB at 40 MHz, with both VGA and IDE on VLB.
50 MHz should be possible as well, with selected VLB cards.
I've always seen such systems as the 'ultimate 486'. I don't think there are PCI-based 486 systems which even allow you to run the PCI bus at 40 or 50 MHz, and if so, if the PCI cards would actually work at those speeds.

Another thing is that VLB is basically connected directly to the CPU. With PCI, you have a controller in the chipset. This adds a bit of extra latency and overhead, so I guess that even at 33 MHz, you may see slightly better performance from VLB.

You're lucky then - that's the exception rather than the rule. I can be confident that any of my PCI graphics cards should work in any of my PCI machines, from a 300MHz Cyrix processor, to a 2.6GHz Core2. Typically the PCI bus can't be overclocked, the whole point being it stay within standard.

Of course, it could be worse. After VLB there was AGP, which at least was mostly well designed but rather limited to one slot.

However, if I remember correctly there were also a small number of motherboards with their own custom expansion slots, and a miniscule number of cards that fit in them.

Alternatively, it could be MCA, which was technically impressive but rather fell down in its implementation, cost and availability.

I've been running 50MHz VLB with ET4000/W32p and Tekram DC680-T flawlessly 😀
But same with S3 805 is a "no go"
So yes, VLB is not a simple mix and match 😁

But I like it, I feel a 486 should be VLB.
PCI on those is just a VLB hack in the end anyway no ?

My elsa winner 1000 trio (PCI) works fine at 40MHz, both under dos and windows. It will also post at 50MHz and complete dos tests, but I haven't tried it at 50MHz under windows.

In fact most of my PCI cards work fine at 40MHz, even my Voodoo cards. Same for VLB. My CL5426 anc 5428 cards both work fine at 40MHz, and the latter even worked at 50Mhz under DOS with a 486 DX 50 on a SiS chipset board. It wasn't stable in windows tought.

As for PCI vs VLB performance, it really depends on how old/new the motherboard is. I have combo PCI/VLB boards where VLB performs better, but trying the same PCI card with a newer UMC board (same CPU) will yeald better results than on the VLB motherboard. (CL5426 VLB vs CL5436 PCI).

Ok, let's try this again:

CPU used on both systems is an Intel DX4 100. Motherboards used - VLB/PCI the FIC 486-VIP-IO and PCI/ISA the Pine PT423b. Same FPM ram used on both boards. Video cards used are a VLB Cirrus Logic CL5426 1MB and for PCI Cirrus Logic CL5436 1MB.

Using the FIC 486-VIP-IO, the VLB card scores better then the PCI card.
Using the Pine PT423b, the PCI card scores better then both the VLB board, and itself on the 486-VIP-IO.

I believe PCI also does bus mastering better than VLB, and also burst transfers (which I have no idea if VLB does or not).

alexanrs wrote:

I believe PCI also does bus mastering better than VLB, and also burst transfers (which I have no idea if VLB does or not).

Yes, VLB had one 'master' slot and usually 2 'slave' slots. Video cards should always go in the master slot 😉
VLB supports burst transfers, there's a 'BLAST' (burst last) and a 'BRDY' (burst ready) signal on the bus to indicate a burst transfer.

The op wanted real results. Numbers are needed to understand the situation.