What is the brown slot at the end of ISA?

[hunterjwizzard]

I don't have a picture up for reference but I've noticed on many ISA motherboards there is sometimes a second slot on the end, usually brown. What is it?

 

[daver2]

I think what you are asking about is the EISA extension connector.

This extended the 8/16 ISA / AT bus to 32 bits - and was normally brown to distinguish it.

See: https://dosdays.co.uk/topics/pc_buses_explained.php

Dave

 

[krebizfan]

EISA was a double decker bus. The ISA connector was the upper set of pins with stops to keep ISA cards on top; the EISA card had a set of cutouts to fall down and connect with both the lower pins and the upper pins to get the full 32 bits. Fortunately, no one changed cards on EISA systems frequently enough to cause the stops to wear out which would cause ISA cards to contact the lower EISA pins.

The extra socket in line with an ISA socket would be either for VLB or dedicated 32 bit memory cards.

Note: IIRC, one of those connectors reused the connector from IBM's Microchannel including the same brown color.

 

[hunterjwizzard]

Thanks.

What would the slot have been used for on a later motherboard with PCI slots?

 

[Eudimorphodon]

I think what you are asking about is the EISA extension connector.

This extended the 8/16 ISA / AT bus to 32 bits - and was normally brown to distinguish it.

Yeah, that reference is flat wrong, that's a VESA motherboard. The VESA extension, as noted, uses the same physical connector as a MicroChannel slot. (Which, in turn, bears a *resemblance* to a PCI slot due to its finer pitch compared to an ISA card edge.) An EISA slot is hard to tell for certain from an above view; the connectors are usually "chonkier" than your typical ISA card edge connector, and from the side they're usually deeper, but you *could* just have some chonky ISA connectors.

The extra socket in line with an ISA socket would be either for VLB or dedicated 32 bit memory cards.

A dedicated 32 bit memory card slot will *probably* have the same 0.1" pitch as the main ISA slot instead of the Microchannel connector. I've also seen motherboards where the additional connector wasn't actually an "additional connector", they just put a longer card edge in place of the shorter part of the 16 bit ISA slot. (Like you might have *2* 62 pin slots right next to each other instead of the 62+36.)

What would the slot have been used for on a later motherboard with PCI slots?

There were a *very few* oddball Pentium (and possibly 486?) motherboards produced that had *both* VESA and PCI slots, so you could use either kind of video card. It was a stupid idea, and the few boards like this that were produced were usually buggy and slow compared to normal boards of either type.

 

[thisisamigaspeaking]

I don't have a picture up for reference but I've noticed on many ISA motherboards there is sometimes a second slot on the end, usually brown. What is it?

It'd be easiest to find an example of what you have seen since it is common. It does sound like you are talking about the VLB/VESA video card slot.

 

[krebizfan]

Thanks.

What would the slot have been used for on a later motherboard with PCI slots?

You should probably post of picture of the specific motherboard you are looking at. There were enough proprietary extensions that you could be looking at a non-standard system.

PCI plus VLB motherboard did exist during that time when PCI was very new. PCI video cards caught on early but other types of PCI cards were less common so proven VLB controllers might be used. Similarly, there were a number of EISA and PCI designs for similar reasons allowing one to pair a reliable EISA SCSI card with a fast PCI video card.

One interesting design point of PCI was that it was possible to have both a PCI slot and an ISA/EISA slot sharing the same bracket. Obviously, only one of the two slots could get a card. I am a bit disappointed that I failed to pick up a used small form desktop with 4 pairs of EISA and PCI slots. Useless slow but really strange.

 

[hunterjwizzard]

It'd be easiest to find an example of what you have seen since it is common. It does sound like you are talking about the VLB/VESA video card slot.

You should probably post of picture of the specific motherboard you are looking at.

This is just an example of one I saw on eBay:


Seller lists it as "Soyo 4SA2".

I don't own this motherboard and am not buying it. I've just been looking around and went "the heck is that brown thing?"

 

[Zare]

VLB.

 

[NeXT]

That's VESA.
VESA or VLB was just a 32-bit(ish) extension that appeared around the 486 era so you could get more performance out of video, storage and I/O cards while not sacrificing a slot for the older ISA bus. While it was somewhat popular for a short while it was famously hard to get working right because bus/CPU speed made some cards unstable and the total length of a card made them a P A I N to get them fully seated. The sweet spot was a 33mhz bus with something like an internally multiplied Intel Overdrive so you were not pushing the chipsets.

 

[hunterjwizzard]

So in theory if I could get my hands on a VLB SCSI card it might perform better than a regular ISA one?

I'm probably not going to do this since it sounds like a PITA, but the concept interests me.

 

[hunterjwizzard]

Sidebar: does "VLB" stand for "Very Long Bus"?

 

[thisisamigaspeaking]

So in theory if I could get my hands on a VLB SCSI card it might perform better than a regular ISA one?

I'm probably not going to do this since it sounds like a PITA, but the concept interests me.

Could be fun. I wouldn't personally, EISA is more interesting to me. And MCA. It was almost exclusively used for video cards. It really wasn't bad at the time, if it worked, but PCI was definitely better and quickly superseded it.

There was a time when over the course of upgrades I had built a mixture of PCI and VLB systems for work and I seem to remember a person who had a VLB complaining a lot about it. Then again, I think I had a VLB as well on my desk and was happy enough with it, although most people had PCI at the time. I may have been overclocking my own system or had a better CPU. I could be misremembering though and she actually had an ISA video card. Not positive. I thought it was VLB.

Sidebar: does "VLB" stand for "Very Long Bus"?

VESA Local Bus, local bus meaning an extension of the CPU's bus I guess.

 

[Eudimorphodon]

Sidebar: does "VLB" stand for "Very Long Bus"?

That was the joke at the time, because it could be a PITA to plug the cards in. But yes, in real life it’s a recursive acronym for V(ideo Electronics Standards Association) L(ocal) B(us).

And yes, this is the same VESA that today dictates things like the bolt patterns for TV wall mounts and whatever.

 

[Eudimorphodon]

So in theory if I could get my hands on a VLB SCSI card it might perform better than a regular ISA one?

Looked up the manual for that Soyo board (pro tip, it's usually pretty easy to find these things), and a thing it says in there is the VLB slot is only for "Slave" cards. This means the slot does not support busmasters, which means it's probably fine for most VESA video cards but probably *not* fine for high performance storage controllers. (I was going to say that VESA SCSI controllers are probably rare as hen's teeth, but there's a DTC 3274 on eBay right now, and, well, the manual says in bold on the front it's a VESA BUSMASTER, so... yeah, you will probably get a sad "whomp whomp" if you try to use it with that board.)

Frankly the only reason those boards existed was to preserve/extend an investment in an expensive VESA video card. (Or to use a cheaper VESA video card in the initial period after PCI's introduction when PCI cards were significantly more expensive than VESA.) You used to see all kinds of dumb things on motherboards in that period, like boards that mostly had 72 pin SIMM slots but would have one set of 30 pin slots so someone who broke the bank buying 16MB's worth of 4MB SIMMs (which depending on when you bought them in the early 1990's might have cost you a king's ransom, the price of RAM was incredibly volatile for a while) could feel like they were getting their money's worth moving them from their old computer, even though it really didn't make sense.

 

[hunterjwizzard]

Ahh ok. So probably no point in seeking out a board with PCI and VLB. God I miss this era of computing.

 

[daver2]

The whole PC scene just got confusing after a while (from a compatibility perspective)...

Dave

 

[Chuck(G)]

I've got a board (forget who made it and I'm too lazy to dig the system out from the pile find out) with an Adaptec 2840 SCSI board and also a Tseglabs VLB video card. By my very subjective estimation, faster than plain ISA, but slower than PCI.

 

[Eudimorphodon]

I already said so in another thread, but in my humble opinion if you really want to experience a 486 it should be a VESA setup.

PCI was basically introduced simultaneously with the Pentium and 486 motherboards with it weren't really a thing until mid-late 1994-ish, at which point 486s were already becoming "Value" products. If you look in a July/August-ish 1994 PC Magazine or whatever that's when you'll start seeing listings for PCI 486DX2/66s and DX4/100s starting to crop up in-between the same CPUs in VESA motherboards and Pentium models, and the takeway you'll sort of come away with is those inital PCI offerings compared badly with both. (More expensive than VESA, but not enough cheaper than a Pentium for what you got.) Most of the PCI 486 boards you'll find like that Soyo board are from more the middle 1995 - early 1996 period, when brand name companies were hardly selling 486 machines anymore but these boards stuffed full of Cyrix and AMD "486+" chips and older/cheaper video cards were still popular with the mom-and-pop-shop/Computer Shopper crowd in the "bargain basement" niche...

... I mean, obviously they're "better", or at least faster, than a late 1993 VESA DX/66 from when you could still call a 486 machine "High End", but I also tend to think of them more of belonging to the Pentium age. The best of them perform about the same as a Pentium 75/Pentium 90 Socket 5/7 machine, and since they use the same video cards and other peripherals they might as well be Pentiums. Except they suck a lot worse at running things like Quake that want a good FPU.

 

[hunterjwizzard]

I already said so in another thread, but in my humble opinion if you really want to experience a 486 it should be a VESA setup.

I get it, but I'm really looking for a more different experience. I've got a PCI graphics card I want to use, and I want to play clock-dependant games. So mixing and matching a couple different eras seems to fit.

It gets very easy to get out of hand with the X is better than Y snowball. Yeah a Pentium I with PCI is going to perform better than a 486. But then we get into well why not a Pentium II, or a III with AGP? I think once you hit the Pentium era you might as well go right to the top. But 486? Hmm.