What are the main differences of Hardcore Mode?

I was curious as to what the differences in gameplay there are between regular mode and hardcore mode?

From what I understand is that you require sleep, food, and water. What are the penalties(other than eventual death) if you are sleep deprived or starved also?

Hardcore mode has a few differences. They fall into three main categories: Sustenance, Healing, and Ammo. In general, the main additonal challenge provided by Hardcore mode is a significantly increased importance in inventory and resource management. Staying within your weight limit while carrying all of the food, water, and ammunition you need to survive becomes a challenge, and you will need to plan your expeditions, and consider what you loot and carry much more carefully. The need to carry Doctors Bags and/or Hydra can add additional strain here. Perks such as Pack Rat become substantially more valuable, as do skills like Survival (as Campfire cooked food is often far more nourishing - and less irradiated - than the pre-war garbage you'll often otherwise rely on.)

For reference, since the term will be used repeatedly, by default, one 'game hour' is two minutes in real time. This can be adjusted by changing the Timescale using the console, or via a mod, but is not recommended for Hardcore Mode players.

Sustenance:

• This is the most widely touted feature of Hardcore mode. Essentially, in Hardcore, you gain three additional meters to watch in addition to your Health. Hunger, Thirst, and Sleep Deprivation. These will rise over time, and upon reaching certain threshholds, you'll be subject to negative effects. (Mechanically, this works very similarly to radiation exposure.) If any of these meters are allowed to reach 1000, you will die.
  • Hunger increases over time, at a rate of 4/game hour and is reduced by consuming any food item. (If an item reduces hunger, it's description on the Pip Boy will read 'FOD -x', where x is the number of points of Hunger reduces.)
    • If your Hunger increases above 200, you will receive a -1 penalty to Strength.
    • At 400, this becomes -2 STR, and -1 Charisma.
    • At 600 this becomes -3 to STR, -2 to CHA, and -1 to Perception.
    • At 800, you'll lose another point of Perception, for -3 STR, -2 CHA, and -2 PER.
    • As with Sleep and Thirst, if you reach 1000 Hunger, you will die.
  • Thirst also increases over time, at a rate of 12/game hour and is reduced by consuming many, but not all beverage items. Several beverages, such as most Alcohol, and Nuka-Cola, and many food items will actually increase your thirst. (If an item reduces thirst, it's description on the Pip Boy will read 'H2O -x'. If it increases thirst, it will read 'H2O +x'.
    • If your Thirst increases above 200, you will receive a -1 penalty to Endurance.
    • At 400, this becomes -2 END, and -1 Perception.
    • At 600 this becomes -3 to END, -2 to PER, and -1 to Intelligence.
    • At 800, you'll lose 2 points of Agility, for -3 END, -2 Agi, -2 PER, and -1 INT.
    • As with Sleep and Hunger, if you reach 1000 Thirst, you will die.
  • Sleep Deprivation increases at a rate of 2/game hour and is reduced by sleeping in a bed, at a rate of -60/hour slept. In addition, there are several items that will reduce your sleep deprivation, most notably sodas such as Nuka-Cola and Sunset Sasparilla and the Atomic Cocktail -- these items are indicated on the Pip Boy with 'SLP -x'.
    • If your Sleep meter increases above 200, you will receive a -1 penalty to Agility.
    • At 400, this becomes -2 AGI, and -1 Intelligence.
    • At 600 this becomes -3 to AGI, -2 to INT, and -1 to Endurance.
    • At 800, this rises to a final penalty of -2 END, -2 INT, and -3 AGI.
    • As with Hunger and Thirst, if you reach 1000 Sleep Deprivation, you will die.

Healing:

• Hardcore mode introduces a few changes to the way healing and healing items work.
  • Stimpaks and other healing items (including food) heal over time rather than instantly. This is represented on the Pip-Boy with a pair of number such as 5hp(12s). This represents the magnitude and duration (in real time, not game time) of the healing effect. Once used, the item will heal you for the first amount, every second, for the duration listed. Thus, 5hp(12s) would heal for 60 health, but over a period of 12 seconds. Multiple healing items will stack. Thus, two 5/12 items will heal for 10 per second over the same 12 seconds.
  • Rad-Away removes radiation poisoning over time. This mechanic is identical to the heal-over-time mechanic for stimpaks.
  • Sleeping provides no healing whatsoever. It does not restore health, or limb condition.
  • Crippled Limbs also can not be healed by stimpaks. The only way to heal a crippled limb is with a Doctor's Bag (which provides less restoration than on normal mode), Hydra (which restores limb condition over time), or by visiting a doctor.
  • Companions will not simply wake up and heal themselves after taking fatal damage in combat. If they die, they stay dead.

Ammo:

• All ammunition has weight. Carrying around a few dozen missiles will leave you severely over encumbered (for instance).