Bochs: A Portable PC Emulator For Unix/X
The set of hardware, CPU, and BIOS features supported by Bochs has been largely determined by the suite of software which I've run within the emulator environment. A lot of my effort has been focused on supporting enough features to run MS DOS 5.0 and Windows 3.1. Recently, I've added Minix 1.7.2 to my list of targeted software. Given this, Bochs currently supports the following items: (Keep in mind that new features are always being added, and some of these may only be available in the next release):
8086/80286 instruction set including protection and virtual memory models. An option to the configuration script allows for compiling for either architecture.
Monochrome Hercules Graphics Adapter (HGA) This is a fairly simplistic graphics adapter with character and pixel mapped graphics capabilities. Text and pixel graphics are mapped to an X window.
Floppy drives: 1.44M 3.5", 1.2M 5.25", and 720K 3.5" These are implemented by mapping them to either Unix files of the corresponding size or to the floppy drive on your workstation. Originally, only BIOS software interrupts (like a subroutine call) were supported, but recently I added a minimal amount of Direct Memory Access (DMA) and floppy I/O support for use with Minix.
Hard drives: 10, 20, or 30-Megabyte drives Hard drives are also implemented as a Unix file. Read and write requests to the hard drive are directed to read() and write() Unix system calls, operating on the hard disk image file. Access to the hard drive is currently limited to BIOS software interrupts. It's likely that use of DMA and hard drive I/O will be added.
Master/slave Programmable Interrupt Controller (PIC) Hardware devices which need to communicate their need to interrupt the CPU to be serviced are attached to either PIC. These include the keyboard, system timer, disk controller, etc. A fairly complete emulation of both master and slave PIC is provided.
Non-enhanced keyboard Keystroke input from the X window used for the video display, provides input for the keyboard emulation. Both BIOS keyboard software interrupt (int 16H) and hardware I/O access are provided. The keyboard code still needs a little work.
CMOS functions I've implemented only a partial set of CMOS functions, although it allows both BIOS software interrupt and hardware I/O access. Primarily, functions which deal with CMOS time, date, and shutdown status are provided. A CMOS real-time clock (RTC) has not yet been implemented.
A fair amount of typical BIOS interrupts and data area values These functions include sensing features and capabilities of your PC, memory size information, reading/writing floppy and hard disk sectors, an interval timer, video functions, a bootstrap loader, etc.
Makefile configuration via GNU 'autoconf'
Runs DOS 5.0, Windows 3.0, Windows 3.1 Additionally, I was able to install and boot up Minix 1.7.2, but more work needs to be done.
There are many more features to add to Bochs to truly make it a useful tool. In the near future, the plan is to focus on adding the 80386 features set, since this will allow Bochs to run up-to-date operating systems, such as Windows 95 and 32-bit code within Windows 3.1. I have other improvements in mind, and I get more ideas from suggestions and input I receive via the Net. Here's a list of additional features I have planned:
386, 486, and other x86 generation features There's a good start on 32-bit emulation already. Coding should progress nicely; testing and debugging will be slower and more arduous. This should allow Bochs to run Minix for 386, Windows 3.1 in enhanced mode, Windows 95, and Linux.
Floating point coprocessor emulation
Mouse emulation I've already got a good start on emulating a PS/2 mouse, but since it's so intimately integrated with the keyboard hardware, it makes debugging the keyboard/mouse code difficult. Mouse code is currently disabled until I revisit it. I'd really like to get good (low-level) documentation on a Logitech or other bus mouse, in which case I'd happily implement it.
File system redirector This would allow DOS or Windows to map a drive, such as E:, to your Unix directory (e.g., /home/johndoe/windows-drive). You'd also be able to read CDs mounted on your Unix file system.
More performance enhancements I'm hesitant to do much in the way of performance enhancements until 386 features are coded, but afterwards, a lot of elements of the code need to be examined for potential performance enhancements. This will be a good time to elicit ideas from the performance wizards of the world.
Linux Journal Annual Archive
Editorial Advisory Panel
Thank you to our 2014 Editorial Advisors!
- Jeff Parent
- Brad Baillio
- Nick Baronian
- Steve Case
- Chadalavada Kalyana
- Caleb Cullen
- Keir Davis
- Michael Eager
- Nick Faltys
- Dennis Frey
- Philip Jacob
- Jay Kruizenga
- Steve Marquez
- Dave McAllister
- Craig Oda
- Mike Roberts
- Chris Stark
- Patrick Swartz
- David Lynch
- Alicia Gibb
- Thomas Quinlan
- Carson McDonald
- Kristen Shoemaker
- Charnell Luchich
- James Walker
- Victor Gregorio
- Hari Boukis
- Brian Conner
- David Lane