I don't have a problem with your original description of a virtual machine...
Joel On Mon, Mar 31, 2003 at 04:59:46PM -0800, Peter Jay Salzman wrote: > hey mike and joel, > > so is there anything flat out wrong with the paragraphs? the intended > audience are readers of the linux gamers' howto who want to know what > things like vmware are. not people taking a course on java. :) > > i prolly should've mentioned that from the start. > > pete > > > begin Joel Baumert <[EMAIL PROTECTED]> > > A virtual machine is essentially an idealized picture of > > how a digital computer and to some extent operating system > > works. You can think about it as an extension of the BIOS > > int 10h or 21h services that provide the same interface to > > hardware. The underlying hardware may be different, but > > programs using the BIOS services don't have to be changed > > to operate. The analogy can be extended to the operating > > system you are running or the libraries that you link into > > your programs. > > > > The "advantage" that something like the JVM provides is > > platform independence because it translates the instructions > > of the program into code that runs on the machine. With > > the JVM you can run the code on another architecture without > > having to recompile the software, something that may be > > impossible outside of the open source world :-). > > > > The "disadvantage" is that code has to be translated and > > requires some level of processing to decode and also places > > the programmer further away from the machine. This distance > > may translate into programs that are written poorly for the > > target architecture. That and it may be impossible to > > get certain things done because you really need access to > > the hardware, which is can be a big issue with embedded > > devices. > > > > > > Joel > > > > > > On Mon, Mar 31, 2003 at 04:30:49PM -0800, Peter Jay Salzman wrote: > > > begin Michael Wenk <[EMAIL PROTECTED]> > > > > On Monday 31 March 2003 12:39 pm, Peter Jay Salzman wrote: > > > > > can someone tell me if this is a formally correct explanation of what a > > > > > virtual machine is? > > > > > > > > > > pete > > > > > > > > > > > > > > > A "real computer" provides an operating system many things, including a > > > > > CPU, I/O channels, memory, a BIOS to provide low level access to > > > > > motherboard and I/O resources, etc. When an operating system wants to > > > > > write to a hard drive, it communicates through a device driver that > > > > > interfaces directly with the hardware device memory. > > > > > > > > > > However, it's possible to give a program all the hardware resources it > > > > > needs. When it wants to access a hard drive, give it some memory to > > > > > write to. When it wants to set an IRQ, give it some bogus instructions > > > > > that lets it think it set an IRQ. If you do this correctly, then in > > > > > principle, there's no way for the application to know whether it's > > > > > really accessing hardware or tricked by being given resources which > > > > > simulate hardware. A virtual machine is the environment which tricks > > > > > applications into believing they're running on a real computer. It > > > > > provides all the services that a real computer would provide. > > > > > > > > > > VM's were used initially in the 1960's to emulate time shared operating > > > > > systems, but these days we use them to run software which was written > > > > > for foreign operating systems, or more commonly, an entire operating > > > > > system. Because of the nature of the VM, the foreign OS can't tell the > > > > > difference between operating in a VM or in a "real" machine. > > > > > > > > > > > > Well, I can't find my old CS book, but I prefer the Java definition for a > > > > VM: > > > > > > > > "An abstract specification for a computing device that can be implemented in > > > > different ways, in software or hardware. ..." > > > > > > > > It goes on to more java and jvm specific information. I think the > > > > important keyword is abstract. You're definition is more specific, but > > > > a VM can describe just about any computing device, and arguably > > > > every computing device may not have the components you listed. > > > > > > > > Mike > > > > > > unfortunately, that definition doesn't really talk to me. :( > > > > > > pete > > -- > Fingerprint: B9F1 6CF3 47C4 7CD8 D33E 70A9 A3B9 1945 67EA 951D > _______________________________________________ > vox-tech mailing list > [EMAIL PROTECTED] > http://lists.lugod.org/mailman/listinfo/vox-tech _______________________________________________ vox-tech mailing list [EMAIL PROTECTED] http://lists.lugod.org/mailman/listinfo/vox-tech
