Half-Life: Day One is the initial pre-release demo of Half-Life. It was designed exclusively for OEM partnerships and was often bundled with graphics cards. Even though it was never available to the general public, it was leaked and Half-Life became one of the most talked about games before even releasing. Half-Life’s proper demo (available free to the general public), is Half-Life: Uplink, which was released several months after the full game.
The demo does have some minor differences from the retail version of Half-Life.
The console and cheats cannot be directly activated, however, there are tricks which can enable it (found in the Trivia section).
Direct3D is not supported (only supports Software mode and OpenGL)
The content stored in the .pak files have priority over the files placed in the actual folders.
The Glock 17 pistol can have an additional round in the chamber after reloading a non-empty magazine, increasing the capacity to 18 rounds.
There is no secondary attack for the pistol; it can only fire in semi-automatic mode.
The Glock 17 has a higher resolution than the retail one's Glock 17.
The Glock 17 doesn't have a reload sound.
The MP5 already has 50 loaded rounds when picked up.
Neither the pistol nor the MP5 reloads automatically after emptying a magazine.
The shotgun does not get 4 extra shells in reserve when picking it up.
Picking up ammunition for the pistol or the shotgun grants the player 30 extra rounds instead of 17 and 12 respectively.
Up to 25 grenades can be carried instead of 10. Additionally, they don't explode in the player's hands if they are cooked for too long, and it is possible to throw them farther than the retail version.
When a grenade lands it plays a satchel sound effect.
The Long Jump Module shown in the hazard course looks like a beta HEV battery with a red color instead of a jetpack.
In the Hazard Course Gina has an extended line for the Long Jump Module.
The HEV battery has a different appearance.
HUD sprites found in the Day One files feature an early RPG icon, an unused battery-style HEV suit indicator as seen in E3 1998 videos, fewer sprites for 320 screen width, and 320x sprites that do not feature the bar near the man showing suit power.
The HECU Laser Tripmine uses the E3 1998 model. Though seen in "We've Got Hostiles" the player never gets to use it as a weapon (since the Tripmine is obtained at the end of "Blast Pit", which is not in "Day One").The table in the cafeteria In "We've Got Hostiles" breaks in half if you hit it or jump on it.Right next to the cafeteria In "We've Got Hostiles", There's a box instead of a table in retail.
The Valve theme (officially known as Hazardous Environments) plays when picking up the MP5 for the first time.
Zoom can be toggled by pressing F11.
When the player reaches the surface in the chapter "We've Got Hostiles", it is daytime instead of sundown.
The access to the storage chamber in the beginning of "Office Complex" (when the shotgun is first found) is not blocked by boxes. The storage chamber itself is also a part of c1a2.
There are more vents in the area where the MP5 is found in the chapter "We've Got Hostiles".
The area seen during the Resonance Cascade in which Vortigaunts surround Gordon is brighter, its walls can be seen with a flashlight and the player's movement is not blocked. In a addition, the textures on the ground are different.
The "screenshot" command saves screenshots in broken 8-bit PCX files, while the retail version saves them in TGA format. "snapshot" command works the same way as in the final version (F8 by default).
Multiple hits with the crowbar are required to kill a barnacle, unlike the retail version which only needs one.
Upward looking is limited like in Quake (because of this, if Gordon is caught in the barnacle's tongue, he cannot kill it until the barnacle inflicts damage).
Blood is flowing (as it is in Half-Life Alpha 0.52) while in retail it is splashing.
Autoaim is enabled by default and cannot be disabled.
The G-man has a different reaction when being shot by the player. If he is fired upon enough times, he will grab his briefcase to his chest level and run, apparently frightened by the bullets.
The HECU troops only feature the beret and the gasmask soldiers, and they do not use the shotgun as their primary weapon.
The death of the Bullsquid features the creature flipping upward, similar to the Headcrab, however in some cases, it utilizes the retail animation.
At the ventilation shaft where the game ends, even if the player tries to reach the bottom vent quickly, it is blocked by a fence thus cutting off access.Some animations in Barney's .mdl file (which can be seen in Half-Life’s model viewer) were cut in the retail version of the game.Every character has beta animations that are not included in the retail version.
If the player accesses the room with the MP5 ammo, the scientist in the freezer room will be alive instead of being dead.
Half-Life Day One has a prototype loading screen. The retail release replaced this with a new loading screen.
Headcrabs have different textures than what's seen in retail release.
Vortigaunts will run in fear if they see the corpses of their own kind.
The difficulties were changed between Half-Life and Half-Life:Day One.
Scientists have less health than in the final release
