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IBM Enhanced Corvette (SCSI) on a Model 55SX

Jamie_S

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Jul 21, 2018
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1
Hi there - looking for guidance on whether its possible to get an IBM "Enhanced Corvette" (Differential SCSI Fast/Wide Adapter) to work in a Model 55SX. I've read ambiguous things online, and some futzing around with reference and options disk has got me to the point that I do now have it at least registered with the system, it now appearing in the View Configuration page of the ref disk, and the system boots (to floppy) with no errors. I should mention the weird proprietary original IBM hard disk is long dead.

Things that concern me are that -
View Config indicates the SCSI card's BIOS is not loaded
Running through Set Configuration errors, indicating that "An error occurred during the installation of the initialisation program"
Running Set and View SCSI devices indicates that "An error occurred while saving the SCSI data."

I currently have no way of attaching a SCSI disk (or expensive SCSI2SD gadget) currently so I don't know if that's the cause of some or all of these errors, but before I waste money on a hopeless cause maybe someone could give me a steer?

Cheers!
 

pinkdonut666

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Apr 18, 2019
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Alberta Canada
You want an adapter like the adaptec AHA-1640 or a future domain adapter with a built in scsi boot rom.

the tribble, Spock, cheetah, corvette etc. will not work in a 55sx unfortunately.
 

WBST

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You want an adapter like the adaptec AHA-1640 or a future domain adapter with a built in scsi boot rom.

the tribble, Spock, cheetah, corvette etc. will not work in a 55sx unfortunately.

I'm afraid that's not quite correct.
The technical requirements, Reference Diskette updates needed and systems supported vary:
https://www.ardent-tool.com/IBM_SCSI/IBM_SCSI.html
https://www.ardent-tool.com/SCSI/SCSI_Adapters.html
https://www.ardent-tool.com/storage_adapters.html
But it is the 8KB NVRAM requirement for the Corvette and Corvette "Turbo" which exclude support of the Model 55SX.
Almost all others are possible. Current draw is more crucial for the 55SX as well.
 

chrispl1974

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May 16, 2019
Messages
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Guys, I am having the same problem. Upgraded my 55SX with a Corvette SCSI Card and a SCSI2SD card. It only works, when the original legacy DBA disk is connected as well. If I disconnect the legacy Hard drive, I get the same errors as Jamie_S.

The funny thing is that it works like a charme with the legacy disk in place. When I do FDISK I get the ESDI-DBA drive as DISK1 and the SCSI2SD Card as DISK2. Any solution yet ? THanks Christian
 

WBST

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Guys, I am having the same problem. Upgraded my 55SX with a Corvette SCSI Card and a SCSI2SD card. It only works, when the original legacy DBA disk is connected as well. If I disconnect the legacy Hard drive, I get the same errors as Jamie_S.

The funny thing is that it works like a charme with the legacy disk in place. When I do FDISK I get the ESDI-DBA drive as DISK1 and the SCSI2SD Card as DISK2. Any solution yet ? THanks Christian

It's because the DBA-ESDI BIOS support is integrated into the system BIOS.Thus, it is impossible to either disable that or ensure the SCSI adapter's BIOS precedes it in memory, to swap drive orders.
 

chrispl1974

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It's because the DBA-ESDI BIOS support is integrated into the system BIOS.Thus, it is impossible to either disable that or ensure the SCSI adapter's BIOS precedes it in memory, to swap drive orders.

Thanks for the feedback. I still think it ought to be possible to change at least the drive sequence, getting a chance to boot from a SCSI drive.

Apparently Peter W. one of the PS2 Gurus from Germany changed the ESDI Adf file
However, the original link with the modified file is not available anymore.

Any thoughts ? Check the Modified ADF for ESDI and SCSI Coexistence paragraph

IBM SCSI /A (ardent-tool.com)
 

WBST

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Thanks for the feedback. I still think it ought to be possible to change at least the drive sequence, getting a chance to boot from a SCSI drive.

Apparently Peter W. one of the PS2 Gurus from Germany changed the ESDI Adf file
However, the original link with the modified file is not available anymore.

Any thoughts ? Check the Modified ADF for ESDI and SCSI Coexistence paragraph

IBM SCSI /A (ardent-tool.com)

I'm afraid you're misunderstanding the difference between the DBA-ESDI controller and drive (@DF9F.ADF) with system BIOS, and the separate ESDI controller adapter (and drives) used in the Model 60 and 80 (@DDFF.ADF plus CDDFF.ADF) which has an on-adapter BIOS chip.
http://www.mcamafia.de/mcapage0/adflist5.htm
 

chrispl1974

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I'm afraid you're misunderstanding the difference between the DBA-ESDI controller and drive (@DF9F.ADF) with system BIOS, and the separate ESDI controller adapter (and drives) used in the Model 60 and 80 (@DDFF.ADF plus CDDFF.ADF) which has an on-adapter BIOS chip.
http://www.mcamafia.de/mcapage0/adflist5.htm

Thanks . I think you are right. I did not consider this difference. So bottom line is that there is no chance to >
a) Run the 55sx with SCSI only
b) run at least the SCSI drive as the primary hard drive while coexisting with the ESDI DBA native disk setup

The native disk is failing and I wanted to install OS/2 1.3 on the SCSI drive.
 

chrispl1974

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May 16, 2019
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By the way, would this mean that I face the same problem when trying to upgrade my Portable IBM P70 ?
 

WBST

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Thanks . I think you are right. I did not consider this difference. So bottom line is that there is no chance to >
a) Run the 55sx with SCSI only
b) run at least the SCSI drive as the primary hard drive while coexisting with the ESDI DBA native disk setup

The native disk is failing and I wanted to install OS/2 1.3 on the SCSI drive.

For a 55SX:
A) isn't possible, it seems. The System BIOS wasn't designed to recognise a failed or absent DBA-ESDI drive. It was a limited low cost design.
B) isn't strictly possible, but could be achieved with a Boot Manager resident on the primary DBA-ESDI drive.
 

whaka

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Feb 26, 2021
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For a 55SX:
A) isn't possible, it seems. The System BIOS wasn't designed to recognise a failed or absent DBA-ESDI drive. It was a limited low cost design.
B) isn't strictly possible, but could be achieved with a Boot Manager resident on the primary DBA-ESDI drive.

i bump this tread :)

another option should be to use the 65sx bios in the 55sx. this is something i'm gonna try soon.
i see no particular reason it wouldn't work. as the V1.05 of the reference diskette is shared between both models.

i tried to make work a "corvette turbo" in the 55, but i guess this one is really a no go. it can't even load the adf, saying there's an error.
edit : in fact i'm doubtful on the exact model, seems it's an enhanced corvette turbo. FRU is 93H7896.

edit bis : of course there's a reason :D
65sx use 128KB eprom, 55sx use 64KB...

yet another edit : ardent tool say 65sx also use 27512 eprom, so, let's try anyway.

and another... don't know what i did, but yes, they definely use the same eprom.
i probably did something wrong when checking files size... they all do 64KB each, for both machine.
really don't know how i get confused.
 
Last edited:

whaka

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well, i think i can say i was young and innocent with PS/2's...
of course, bioses of the 65 or 55ls don't want to work like that in the 55sx, would be too easy :D
 

chrispl1974

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well, i think i can say i was young and innocent with PS/2's...
of course, bioses of the 65 or 55ls don't want to work like that in the 55sx, would be too easy :D

Good effort. Thanks for trying anyway. In the meantime did anyone have luck booting from a SCSI drive in a 55SX ?
 

whaka

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i'm more or less continuing working on.
but i think i'll forget the enhanced corvette. in my case i can't even load the adf.

i buyed an extra 2K sram (dallas DS1220), from my understanding it might be useful for storing scsi configuration, and booting on external scsi instead of esdi.
maybe the 65 bios will work too with this the extra sram, don't know, really but i'll try :D

but i think it's better to go with a more contemporary controller, like the spock for exemple.
this one has better chance to be bootable in a 55.
 

whaka

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and i bump.
the "patriot" controller work like a charm in the 55sx. this is the future domain MCS 700 with a custom rom made by ibm.
the ibm name for it : SCSI-2 Adapter/A.



this rom support at least 8GB drives. i tried with a 8GB compact flash, and it work.
maybe it should support larger size, i'll try this when possible.
 

IBMMuseum

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i buyed an extra 2K sram (dallas DS1220), from my understanding it might be useful for storing scsi configuration, and booting on external scsi instead of esdi.
maybe the 65 bios will work too with this the extra sram, don't know, really but i'll try

The Model 55SX doesn't have 'Extended CMOS' (as well as the 286-based Models 50-021 and 50Z) - this limits them to four microchannel slots and can affect certain adapters that require more POS configuration storage. You are correct that you can add a DS1220 (that *IS* the 2Kb NVRAM chip for Extended CMOS) to a 'Type 2' 55SX planar (the older 'Type 1' planar doesn't have the socket), but you need the Model 55LS BIOS (dated the same as the 65SX BIOS) to use it. I've been meaning to do this conversion (without the 55LS riser swap that changes the planar ID and makes it so the 55SX Reference Diskette doesn't work) too.
 
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