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ISA v. EISA

OldTimeCoder

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I had two EISA computers, a Del (PC Limited) 386 and a Compaq 486. Both had EISA architecture. The EISA slots were backwards compatible so you could use an ISA adapter. I don't have the computers anymore as both died a tragic death, drowned in a flood. But with luck some parts were saved as both were disassembled for upgrads and repair. That was back in 2000.

Recently going though my old parts bins I found 14 old SCSI drives and these two old SCSI adapters that were in those two computers. Unfortunately I do not have a EISA motherboard to test these in but do have a couple older computers if these EISA cards would work in an ISA slot.

Question is would they work in an ISA slot.
 

krebizfan

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EISA cards won't work in ISA slots. But check the cards anyway just in case those were ISA cards; it did happen especially with early EISA systems that were sold before working EISA expansion cards were manufactured.
 

Chuck(G)

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I don't think so--the EISA connector pitch is half that (it's a 32-bit bus) of the ISA (16-bit bus), so even if it was physically possible to jam an EISA card into an ISA slot, it still wouldn't work.
 

Chuck(G)

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Perhaps something like this? (Adaptec AHA-1740, a very common EISA SCSI controller)

800px-KL_Adaptec_AHA-1740_SCSI.jpg
 

RBARDY

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if you look at chuck[g] photo of the controller the top half of the slot is 16 bit isa while the botton is 32 bit eisa which is deeper so a isa scsi will fit in a eisa board but only a eisa card will fit to the bottom and get 32bit contact i have eisa esdi and eisa scsi controllers and will list them eventually on my website pcequip.com
 

Chuck(G)

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Yes, my point was that even if you decided to grind the bottom half of an EISA board connector off so that it fit in an ISA slot, it still wouldn't work.
 

OldTimeCoder

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Perhaps something like this? (Adaptec AHA-1740, a very common EISA SCSI controller)

800px-KL_Adaptec_AHA-1740_SCSI.jpg

Close, I have the AHA-1740a which includes a floppy controller on the card. I looked for a EISA motherboard but they are too expensive for what I need or want, will probably put them up on ebay and buy a SCSI card.
 

Chuck(G)

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Thanks for the confirmation. The only difference between the 1740 and 1740a is that the floppy components are populated. The naming convention differs a bit with the ISA cards. An AHA-1540 ISA controller, for example, has the floppy components unpopulated; an AHA-1542 is the same card but with floppy components. On the other hand, a 1540A, B or C are simply later revisions of the controller.
 

twolazy

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I own 2 scsi cards this model, that are a later revision I believe B or C rev (if I recall correctly, both have floppy controllers), and both work fine on reg isa believe it or not! Difference is, the overall disk speed off the card. Isa puts out 1/2 the bandwidth of EISA. Think of it like PCI-E 1x and 16x. Both are basically the same thing, one is just faster with more connections. Same applies here. Guarantee you can use that card in a regular isa system. =)

Now not all EISA cards are backwards compatible, due to relying on the extra connections, but these early adaptec were...
 
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IBMMuseum

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I own 2 scsi cards this model, that are a later revision I believe B or C rev (if I recall correctly, both have floppy controllers), and both work fine on reg isa believe it or not! Difference is, the overall disk speed off the card. Isa puts out 1/2 the bandwidth of EISA. Think of it like PCI-E 1x and 16x. Both are basically the same thing, one is just faster with more connections. Same applies here. Guarantee you can use that card in a regular isa system. =)

Now not all EISA cards are backwards compatible, due to relying on the extra connections, but these early adaptec were...

It might have to do with the model numbering with Adaptec:

14xx was PCMCIA-based
15xx was ISA-based
16xx was MCA-based (limited to 16-bit, which I only know of the AHA-1640)
17xx was EISA (non-Bus Mastering?, maybe ISA-compatible?)
27xx was Bus Mastering EISA (most likely non-ISA compatible)
29xx was 32-bit PCI

If the last number of any of those lines was '0', it didn't have the floppy controller, '2' (i.e. 1742) did...
 

MaTel

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I own 2 scsi cards this model, that are a later revision I believe B or C rev (if I recall correctly, both have floppy controllers), and both work fine on reg isa believe it or not! Difference is, the overall disk speed off the card. Isa puts out 1/2 the bandwidth of EISA. Think of it like PCI-E 1x and 16x. Both are basically the same thing, one is just faster with more connections. Same applies here. Guarantee you can use that card in a regular isa system. =)

Now not all EISA cards are backwards compatible, due to relying on the extra connections, but these early adaptec were...

I think you're wrong. The EISA slot is backwards compatible to ISA cards but EISA cards are not backwards compatible to ISA slots. EISA Boards are are jumperless and are only configurable with the EISA-tool. But how do you configure a EISA-Board in a ISA system?
 

twolazy

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I think you're wrong. The EISA slot is backwards compatible to ISA cards but EISA cards are not backwards compatible to ISA slots. EISA Boards are are jumperless and are only configurable with the EISA-tool. But how do you configure a EISA-Board in a ISA system?

Sorry, but I am not mistaken. I have used this EISA card in an isa system with 0 problems. Even the manual states you can... Standard mode btw is ISA mode. See page 1-5 for validation. BTW 15xx series cards are ISA based.

See page 1-5
http://download.adaptec.com/pdfs/user_guides/aha1740a_um.pdf

The AHA-1740A/1742A/1744 has two modes of operation: standard
mode and enhanced mode. The standard mode is software
compatible with the AHA-1540 series host adapter drivers. The
enhanced mode uses an advanced, high performance mailbox
interface and features full EISA 32-bit addressing. The
AHA-1740A/1742A/1744, in enhanced mode, can support up
to 4 Gigabytes of host RAM memory. The two modes of the
AHA-1740A/1742A/1744 are selected by running the EISA Configuration
utility provided with every EISA machine. In general,
the enhanced mode of the AHA-1740A/1742A/1744 should be
used, whenever possible, for maximum performance.

Standard Mode
(ISA compatible mode)
Enhanced Mode
(enhanced mailbox interface)

For the card to work in ISA mode, you must use the built in utility, and change to Standard mode. After doing so, the card will be bootable in a ISA based system. Like I said previously, it will reduce the overall bandwidth of the card by about 1/2. Also, you can only use I think 2 drives in ISA mode that are bootable, instead of 7. Bout all I recall off top of my head. Bonus is the floppy controller will still work, and supports 4 drives! ^_^ Whole reason why I know it works to be honest. I used it in a 386 system to have 4 fdd's and 2 scsi hdd's (system was used to clone floppy diskettes with diskcopyfast).

Just trust me here, anyone who says it wont work is mistaken. It WILL WORK FINE in an ISA slot, at least mine did. No need to grind down the card either... Whole situation reminds me of the soundblaster 16 in 8 bit slots fiasco. I swore for years they worked fine in 8 bit slots, most told me I was mistaken. Yet we know the truth round here now, don't we? xD

Now that all this background info is out of the way, let me go find my 2 EISA adaptec cards. I'll post the model number.

Edit: Found them. Adaptec AHA-1740/42A - ASSY 467806-00 Rev H


If anyone still doesn't believe me, I shall make a video and post it on youtube, using a 286 that definitely could have never had EISA, just to put this to rest...
 
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njroadfan

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It might have to do with the model numbering with Adaptec:

14xx was PCMCIA-based
15xx was ISA-based
16xx was MCA-based (limited to 16-bit, which I only know of the AHA-1640)
17xx was EISA (non-Bus Mastering?, maybe ISA-compatible?)
27xx was Bus Mastering EISA (most likely non-ISA compatible)
29xx was 32-bit PCI

If the last number of any of those lines was '0', it didn't have the floppy controller, '2' (i.e. 1742) did...

You can add 28xx for VESA Local Bus. The 0 = no floppy and 2 = floppy convention applied to those cards too. There was also an APA-1350 parallel to SCSI adapter (rebranded Shuttle EPST chipset, although Adaptec only provided Win9x/NT drivers, the Shuttle DOS/2K drivers worked with it).
 
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MaTel

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You can add 28xx for VESA Local Bus. The 0 = no floppy and 2 = floppy convention applied to those cards too. There was also an APA-1350 parallel to SCSI adapter (rebranded Shuttle EPST chipset, although Adaptec only provided Win9x/NT drivers, the Shuttle DOS/2K drivers worked with it).

It might have to do with the model numbering with Adaptec:

14xx was PCMCIA-based
15xx was ISA-based
16xx was MCA-based (limited to 16-bit, which I only know of the AHA-1640)
17xx was EISA (non-Bus Mastering?, maybe ISA-compatible?)
27xx was Bus Mastering EISA (most likely non-ISA compatible)
29xx was 32-bit PCI

If the last number of any of those lines was '0', it didn't have the floppy controller, '2' (i.e. 1742) did...

17xx is a bus master device
 

MaTel

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Sorry, but I am not mistaken. I have used this EISA card in an isa system with 0 problems. Even the manual states you can... Standard mode btw is ISA mode. See page 1-5 for validation. BTW 15xx series cards are ISA based.

See page 1-5
http://download.adaptec.com/pdfs/user_guides/aha1740a_um.pdf



For the card to work in ISA mode, you must use the built in utility, and change to Standard mode. After doing so, the card will be bootable in a ISA based system. Like I said previously, it will reduce the overall bandwidth of the card by about 1/2. Also, you can only use I think 2 drives in ISA mode that are bootable, instead of 7. Bout all I recall off top of my head. Bonus is the floppy controller will still work, and supports 4 drives! ^_^ Whole reason why I know it works to be honest. I used it in a 386 system to have 4 fdd's and 2 scsi hdd's (system was used to clone floppy diskettes with diskcopyfast).

Just trust me here, anyone who says it wont work is mistaken. It WILL WORK FINE in an ISA slot, at least mine did. No need to grind down the card either... Whole situation reminds me of the soundblaster 16 in 8 bit slots fiasco. I swore for years they worked fine in 8 bit slots, most told me I was mistaken. Yet we know the truth round here now, don't we? xD

Now that all this background info is out of the way, let me go find my 2 EISA adaptec cards. I'll post the model number.

Edit: Found them. Adaptec AHA-1740/42A - ASSY 467806-00 Rev H


If anyone still doesn't believe me, I shall make a video and post it on youtube, using a 286 that definitely could have never had EISA, just to put this to rest...

I'm surprised, because Adaptec speaks only from software compatibility to AHA15xx drivers not from hardware compatibility to ISA slot. The standard and enhanced configuration is only possible with a EISA board.
 
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