Subject: Re: XFree 2.0?
To: None <bachesta@genesis.Data-IO.COM>
From: Havard Eidnes <>
List: current-users
Date: 11/14/1993 13:42:11
> I have been having a problem with reboots on my machine with 20 Megs
> of RAM. When I bring it down to 16 Megs it seems to works ok. Initially I 
> thought it was bad RAM, althoug the RAM worked fine before I installed
> the XFree 2.0. I have since replaced the RAM with no change. At the same 
> Time I upgraded to XFree 2.0 I upgraded the disk controller from the 
> standard AT MFM to an Adapted 1542 SCSI controller. I have been assuming 
> the problem is with the controller, although I have no proof of this, 
> or no idea what may be going wrong. A reboot dosen't leave much of
> a trail to follow. Anyway I hope this helps.

It is the SCSI controller and driver software which isn't able to cope with
more then 16MB memory.  The problem is that ISA bus DMA devices can only
address 16MB of physical memory, and if the buffer the driver is trying to
transfer to is in the 16-20MB range of physical memory, you will most
likely overwrite some random area in the 0-4MB range instead.  Not too

There has been talk about creating "bounce buffers" or something else
(making sure the whole buffer cache is allocated in physical memory in the
0-16MB range? I have no idea if this is feasible...) to be able to use ISA
DMA devices in >16MB systems, but I do not know if anything is happening in
this area right now.

- Havard