TMC850 Maximum Drive Size

[GrizzlyAdams]

I've got a TMC850 and BIOS version 8.5 in my XT. Anyone know what the maximum size drive I can safely access is? I've been having issues with a 4GB drive even when using a couple of 128MB partitions (never anything past 512MB).

 

[Anonymous Coward]

I've got a TMC850 and BIOS version 8.5 in my XT. Anyone know what the maximum size drive I can safely access is? I've been having issues with a 4GB drive even when using a couple of 128MB partitions (never anything past 512MB).

Wait, you have BIOS version 8.5 working in an XT? I thought 8.4 was the last one, and I remember it required a 286 CPU.

 

[Timo W.]

Maybe his XT has a NEC V20 cpu.

 

[Chuck(G)]

Various postings around the web seem to suggest that 2GB is the limit. However, make sure that you've done your SCSI homework; i.e. make sure that your drive is terminated correctly. There's lots of voodoo in SCSI that can trip you up if you're not careful.

 

[GrizzlyAdams]

Wait, you have BIOS version 8.5 working in an XT? I thought 8.4 was the last one, and I remember it required a 286 CPU.

PCXTBIOS from PhatCode comes bundled with a TMC850 v8.5 ROM that works on XT (at least when used with derivatives of that System BIOS).

I also found out that writing to the disk when the CPU is at 8MHz causes a GPF, but at 4.77 all is good. I might make a patch to the TMC850 ROM that turns the clock speed down when entering, and restores it after exiting the interrupt handler.

After getting tired of re-imaging my 4GB drive over and over again, I used SeaTools enterprise to set the capacity limit to 999 cyl, 64 heads, 32 sectors. Since doing that I've not seen anymore corruption.