• the original game required somewhere between ten and twelve megabytes of RAM, including the loading of the program into memory. The DS has just four megabytes of general-purpose memory - not cool.
• the original game was software-rendered, something which requires a decent amount of computational power, something the DS doesn't have.
• the original game required a math co-processor (also known as an FPU). Neither processor in the DS has an FPU so all floating-point operations must be emulated, which is very slow.

• the game runs on, like, every other platform in the entire world, right?
• the DS has hardware which can accelerate 3D graphics
• the DS has a wireless interface built in - anyone for DS-DS deathmatches?
  

The game

• the program, working state and game data have been squeezed into the four megabytes of main memory
• it requires either shareware or commercial pak files, Amiga and PC paks have been successfully used
  
• many total conversions and mods should work with a stock DS, assuming they respect the tiny memory size
• total conversion and mods which refuse to play on a stock DS will play on a DS with a compatible flash card when combined with the EXRAM build
  
• infrastructure-based wifi network gaming is supported
  
• ad-hoc DS/DS gaming is currently de-activated in this version
  
• there is full control configuration
• game saves work, although there may be some corruption using certain DLDI drivers - game saving is not guaranteed to work correctly in the EXRAM build (when used with a slot-2 DLDI)
  
• there's a crosshair
• there's view snapping and pen sensitivity settings
  
• there is a proper timebase, so the speed won't be inconsistent any more like it was in pre1
  
• there's an on-screen keyboard, for use in-game and with the console, and it is much more functional than before
  
• there are eight user-bindable 'touch buttons'
• access to the command line is now easier
• dodgy QuakeC compatibility has been improved
  

Graphics

• all software renderering has been moved over to using the DS' 3D hardware
• world textures are display 99% correctly, there may the occasional non-power-of-two texture wrapping glitch; Alias models are fully textured
• sprites (eg explosions) are now correctly rendered, and they now have their correct animated textures (ie they're not pink any more!)
• particles (eg blood effects) are also correctly rendered, and also come in a shade other than pink
• animated model skins are now (barely) supported
  
• the game uses faux vertex lighting, derived from the original lightmaps; light animations also work correctly
  
• there's no dynamic lighting and Alias models are not lit
  
• there are sky, water, sludge, lava and teleporter animations (the sky is now rendered correctly)
• the console now uses the Quake font from the chosen pak files
• the game uses hardware fogging for a light depth cue above ground, thick fog for below water
• there's a HUD
• GUI elements are transparent (with no more corruption)
  

Sound

• there's a full-blown custom ARM7 sound effects system, and it totally r0x0rs
  
• the sound system uses proper spatial positioning (it is stereo though...) - plug it into your speakers and subwoofer to hear all the effort I put into this!
• CD music has been dropped from this version...it may return
  

Tech info

• uses the libfat DLDI interface, so should hopefully work on all supported flash cards
• built using the devkitARM r20 toolchain
• textures and sounds are loaded from disk on demand - you will notice slow loading if you have certain types of cards, or low quality flash cards
• sound and texture memory is defragged in the background
  
• in-game performance has been improved but is still not hot, and I think this is as good as it's going to get
  
• rendering performance is very good (pause the game and move the camera if you don't believe me)
  
• performance is timed using a custom function-instrumenting profiler (a bit like gprof) and another system is used for recording the exact pad and screen input for later replaying
• the DS is put to sleep when the lid closes (disabled in this build)
• there is no texturing on brush or Alias models or images loaded from individual files - you must use pak files