RT Linux is a completely different operating system from Linux. It is built to run before Linux. This means that whenever any system activity occurs (e.g. timer event or hardware event) RT Linux gets that activity. If there is a RT Linux process that is affected by that event then it will run, possibly preempting Linux.

RT Linux provides a process model, scheduler, process synchronization primitives, interrupt handlers, its own incompatible programming API, and a small subset of the system features normally associated with a complete OS. RT Linux processes communicate with Linux processes through shared memory and a special pipe mechanism, so if you intend to use any facility offered by Linux (such as files system access, GUI access, TCP/IP or more importantly, any of the hardware device drivers offered by Linux) then you have to ...

- The only things that we have seen change between QNX 4.23 and 4.25 that might affect a Cogent customer are mqueue, and TCP/IP. If you know you are not using these in your related applications, then you should be fine. If you are using mqueue, then you need to backdate it to version 4.24A, I believe. The techs at QNX can help you out. If you are using TCP/IP then you will probably only notice a stability improvement, and might possibly have to alter /etc/resolv.conf. It is likely that you will have to do nothing special after an upgrade.

QNX 4.25 is a free upgrade from 4.23. You will not have to pay for it. You can download it from ftp.quics.com if you have a QUICS account. If you do not, then you should talk to your customer service representative there to get an account, or try their web site at www.qnx.com.

The latest version of QNX Windows can be run on many new video cards, including most ATI Mach 64 (Rage) and Rage 128 cards, and some Matrox cards. You use the Photon graphics drivers and the gr.photon QNX Windows drivers. There is also a graphics driver for QNX Windows that uses the Scitech video drivers, but you will need to buy an inexpensive license to run them in accelerated mode. You are not stuck with Mach 32.

QNX 4.25 will support any size of hard drive. Be sure to upgrade to 4.25D when you upgrade the machine. Your QNX partition can be up to 8GB in size without crossing the 1024 cylinder boundary in LBA mode, which you will need to use. Try to buy a 10GB drive, and partition it.

If you have any trouble due to BIOS limitations in the computer, you can upgrade your BIOS, and do:

We recently upgraded 3 vintage 1997 computers from QNX 4.23 and an old QNX Windows to the latest QNX 4.25D and the newest QNX Windows, and ran them with ATI Rage Pro Turbo AGP cards and new 10GB Fujitsu hard disks. They ran our QNX Windows, TCP and non-windows applications without modification. We failed to upgrade a 1996 computer because it would not boot with the hard drive in LBA mode (not QNX's problem), and we needed that to get the necessary disk space. We are replacing the motherboard on this one, and don't expect any problems at all. We routinely run QNX Windows with Mach64 based cards using the Photon drivers on Celeron 333 computers and Pentium II 450 computers.