What I learnt putting a (Blue)SCSI in an IBM AT (5170) With Adaptec AHA-1520

[Getafix]

I knew almost nothing about this, and this is what I learnt, documented here should I or someone else need it again later:

1) My BIOS (01/10/84 U27=6181028, U47=6181029) would not work. Could not boot from SCSI. Replaced with AMI BIOS.
a) EZ-SCSI did not see my Adaptec card till I replaced the BIOS
b) I am using MS-DOS 6.22
2) SCSI drives show up after the PC BIOS configured hard drives
3) On my Adaptec AHA-1520 (using its BIOS, other adapters may vary - maybe map 4 DOS drives or something):
a) I left all but 2 jumpers at factory settings (see below) but only 1 change did anything
b) Only SCSI ID 0 & 1 are mapped to DOS (so use fdisk to partition), with no PC BIOS HD present
b.1) PC BIOS drives show up first and at most 2 SCSI disks in the slots left over out of max 2 DOS slots
b.2) Any SCSI drives not mapped to the 2 possible DOS slots can be used through ASPIDISK.SYS
c) The J5 R- jumper to "Enable/disable greater than 1 GB translation" didn't do anything for me
c.1) These "DOS mapped drives", if using BlueSCSI (and I presume SCSI2SD) weren't usable bigger than 1024M
c.2) Use a file size of 1025M for SCSI IDs 1 & 2 (Unless > 1GB translation works for you, I guess, on DOS mapped drives)
c.2.1) a 1025M file is 1024M in fdisk and formats to 1023.98M. 1024M file size does a little less
d) SCSI ID 2+ disks (or any non-SCSI BIOS to DOS mapped drives)
d.1) The max usable file size for non-DOS mapped (usually SCSI ID 2+) is 8040M.
d.1.1) Anything bigger and AFDISK sees > 1024 Cylinders and will just ignore that "area" of disk
d.2) you need ASPIDISK.SYS (which needs ASPI2DOS.SYS or whatever variant for your card) to see them
d.2.1) add /D (ex. DEVICE=ASPI2DOS.SYS /D) to the call on both for useful info
d.3) To partition use AFDISK from EZ-SCSI
d.3.1) for 8040M files I used end cylinders of 260,521,782,1023 for 3x 2047M and 1x 1890M partitions
e) Jumper J5 M1 (Enable Fast SCSI) turned off a lot of SCSI BIOS prints and waits and made the boot go way faster
h) PC-TOOLS' SI reports a disk rating of 31 to 32 (normal is 5.2 for AT @ 6MHz) and transfer speed of ~933 Kb/Sec
h.1) I used SCSI ID 0 & 2 skipping 1 (and no BIOS HD).
h.2) If I add an ID 1 disk, SI reports 29.1 and ~873 Kb/Sec on both drives. Who knows why it changes?

I used the Unix utility truncate (also in wsl or installed with Git under windows) to make empty files on the SD card to use with BlueSCSI. Syntax is:
truncate -s <size> <file> where size is something like 1025M or 8040M or 8G or whatever. File is HDx.hda where x is the SCSI ID (example HD0.HDA)

So, steps would be:
Jump > 1 GB jumper (and maybe it does something)
Make files on SD
Install SCSI & BlueSCSI
Boot and install DOS
Install EZ-SCSI
use AFDISK
Jump "Fast SCSI" jumper (or do it earlier but it helped me to see the bios do things)
and you can have a lot of pretty fast disk space!

Thank you
Stefan

 

[VERAULT]

I have been playing alot with blueSCSI in the past 6 months as well. I built 4 units. Honestly it seemed great at first but only in the past month did I realize I was getting terrible data corruption. I had to keep repairing the hard drive volumes. I replaced it with a SCSI2Sd ver 5.1 and all those issues vanished. I tried it on all my BlueSCSI devices with various SD cards. I dont know what the deal is but they didnt work out for me. I was using them all on various old MAC's.

These "JUMPERS" you mention.. I take it they are on the adaptec card? You didnt specify.

 

[Getafix]

Hi,

These "JUMPERS" you mention.. I take it they are on the adaptec card? You didnt specify.

Yes, all jumpers I talk about are on the Adaptec card. The card has a lot of jumpers but most seem to make sense in the default settings. I did try to move the IRQ and the address the Adaptec BIOS gets mapped to, to see if I could get it to work while I was on the original BIOS. The jumpers worked but the card still didn't work with the old PC BIOS. It would say "Starting MS Dos" and would just hang at that point after polling the two floppy drives.

I was using them all on various old MAC's.

I have a few of both, mostly also on old Apple stuff. The SCSI2SD on my IIgs is used almost daily and has been rock solid for many months. I hope the BlueSCSIs keep working for me - so far absolutely no issues in a NextStation and Centris 650, as well as on this AT. Time will tell. I prefer the BlueSCSI to the SCSI2SD for ease of use but if not reliable, none of that will matter. I didn't build my own, I bought pre-assembled. Not saying that's going to make a difference though

Thank you
Stefan

 

[1ST1]

h.2) If I add an ID 1 disk, SI reports 29.1 and ~873 Kb/Sec on both drives. Who knows why it changes?

I potentially have an explanation why the disk is slower that way:

When it is served by the SCSI bios, the BIOS code is executed from a slow EPROM chip which has only 8 bit data lines. When the drive is served by ASPI2DOS, ASPIDISK, these drivers are sitting in "fast" 16 Bit DRAM. Mainly the 8/16 bit access should make the difference. Don't forget, with the 152x controller the 286 CPU does all the SCSI traffic in PIO mode, controlled by BIOS or driver. The 1520 controller was a kind of low-cost SCSI controller which does not support DMA. The 1540/42 controllers can support DMA and depending on the generation of 154x (A/BC), they reach 2 or 8 MB/s.

By the way, I didn't expect the 1520 controller to reach allmost 1 MB, that is still faster than I expected.

 

[Getafix]

Hi

The 1520 controller was a kind of low-cost SCSI controller which does not support DMA.

Cheapest I could find! However, it does have jumpers to enable DMA but the manual says that DOS & Windows won't support DMA, only OS/2 does. So, I didn't bother trying to use DMA - this is just a DOS machine.

The 1540/42 controllers can support DMA and depending on the generation of 154x (A/BC), they reach 2 or 8 MB/s.

Is there a way to get DMA working with DOS, or were you just talking speed using another OS?

By the way, I didn't expect the 1520 controller to reach allmost 1 MB, that is still faster than I expected.

Yeah, not too shabby, eh!?

Thanks
Stefan

 

[1ST1]

The 154x are that fast in DOS as they support DMA. 154xA/B 2 MB/s, and 154xCx can reach 8 MB, depending on drives, and it is better to have a 486 to reach that speed.