Wednesday, Debtember 08, 1999
Fastest Proprietary 80x86 Based Operating System
So the Slashdot crowd are raning about this new operating system called V2 OS. Since one of my many little hobbies is collecting and critiquing homebrew/alternative operating systems, I decided to give this one a try.
It seems that you can only get a binary so I can't comment on the code quality (all 80x86 Assembly code of course) but I did try to boot it. I have a spare 486 that normally runs a network monitor I wrote (one of these days I'll get around to releasing it) but hey, it's a PC and it'll spare me the trouble of rebooting my main system.
V2-OS ...................OK System16 code is now in control. ERROR: Failed to retieve [sic] information on the bootdisk...[1] Creating PartitionList. ERROR: Failed to retieve [sic] information on the bootdisk...[4]
[sic]'s are mine
Can't quite understand why it failed. Linux boots fine from floppy on this system. The only unusual thing about the system (other than it being a Compaq 486) is the lack of a harddrive (I actually use a modified tomsrtbt distribution—it's a nice single disk Linux distribution that makes a very good rescue disk for PCs). Everything else on the system is pretty much vanilla PC.
The last “Fastest Proprietary 80x86 Based Operating System” they featured at least came with source code. A good thing because it's long gone. All the links I have to it are no longer valid. I wonder how long this one will last?
Exclusion
For those of you who are interested in rolling your own operating system, and if you insist on writing it all in Assembly on your typical IBM PCompatible (and the most popular type is your 32-bit multitasking operating system) please, please, do yourself a favor—avoid using CLI and STI as locking primitives. It fails miserably on SMP-based machines (which I predict will become a commoditized item, much like older 486 and early Pentium machines are now, in the next five years).
Better to use the following:
lock_for_here db 0 ; code code code mov al,1 .spin xchg al,[lock_for_here] cmp al,0 jne .spin ; critical code here ... mov byte ptr [lock_for_here],0
This actually has several advantages over using CLI and STI:
- XCHG locks the bus so that the exchange is atomic with respect to other CPUs on the bus.
- XCHG is not a protected mode instruction, unlike CLI and STI—therefore the sequence can even be used in non-priviledged code. While this may seem silly when you're writing a kernel, not every CPU has a duo user/superuser model. The 80x86 line does support four different priviledged modes.
- Interrupts can still be serviced.
- It doesn't hurt that much on a single-CPU system if it's programmed properly. Sure, the worst case is a deadlocked system, but you're careful to avoid deadlocks, right?
Better yet, wrap them up into functions. That case, if you do need to change how to lock critical sections (say if CLI/STI does prove faster for a single CPU system) you can easily change it in one location.
And it makes it just that much easier to port.
