Storage Deck Upgrade

A Storage Deck Upgrade (or SDU) is an upgrade item that can be applied to a character's inventory to increase that character's storage capacity. The different types of SDU that players will interact with include a Backpack SDU and a number of different weapon SDUs. Another class of SDU is referred to as a "Weapon Slot Storage Deck" is automatically applied to a character without the need for player interaction.

Backpack SDU
The Backpack SDUs each offer 3 additional slots of storage capacity. Each one is gained as a reward for completing one of the ten Claptrap Rescue Missions, for an extra thirty spaces of storage that can be earned throughout the game to a total capacity of 42 on the first playthrough.

Once players complete the story on a first playthrough the higher difficulty second playthrough will allow them to repeat the Claptrap Rescue Missions for more Backpack SDUs. Unlike the first playthrough, only the first five of these quests (Safe House, The Lost Cave, New Haven, Tetanus Warren, Scrapyard) offer a chance of getting an extra SDU when completed. This can take several tries from either exiting without saving or loading from a backup file due to the SDU reward not being 100%. But it is possible to get the Repair Kit first (tested for the stated first five Claptraps in playthrough 2). That way you don't have to start the complete Claptrap Rescue Missions over and over again and just have to deliver the Kit. These additional Backpack SDUs are often refered to as glitches by players in Borderlands community forums, however Gearbox has not released any information confirming the additional SDUs to be glitches, and they appear to be intentional 'Bonus' SDUs that players have a chance of obtaining. (These "Bonus" SDUs from the second playthrough appear to have been eliminated with the latest patch (1.3.0){ disputed see talk page}) The appearance of these SDUs being an intentional addon is the PC confirmed programming that deliberately increases the chances of obtaining these 'random' SDUs if the player has less inventory slots already, or has more inventory slots filled when turning in the Mission for the reward.

The original total maximum inventory slots is 57 on the game disc alone, but with the release of the "Zombie Island of Dr. Ned" DLC including an additional Claptrap to save, the new maximum is 63. You can receive the two extra upgrades by accessing the DLC from each main game playthrough (one per playthrough).

In Secret Armory of General Knoxx the Claptrap in Lockdown Palace has a chance to reward a Backpack SDU in Playthrough 1 (much like playthrough 2 in the regular game), brining the latest inventory maximum to 66. Playthrough 2 has not yet been seen to reward another backpack upgrade.

Weapon Equip Slot SDU
Two Weapon Equip Slot SDUs are available as quest rewards in Playthrough 1. Together these increase the weapon equipping capacity of a character up to four weapons, allowing an improved selection of weapons in the thick of a fire fight. Each weapon equip slot provides self-contained 'storage' of one weapon in addition to the inventory capacity.

The two quests that offer these as rewards are:


 * Return To Zed
 * Road Warriors: Bandit Apocalypse

Ammunition SDU
Eight other SDU types that players interact with are SDUs for increasing a character's ammunition storage. These SDUs are purchased from Ammo Vendors and have quality levels that increase in the same manner as weapon quality, indicated by colour. Characters gradually unlock higher quality weapon SDUs as they increase in level and progress through the game. The higher the quality, the greater the capacity and the higher the cost.

These do not have to be bought in order as they appear in game. If you buy a higher capacity SDU before a previous one, it will jump up to the higher one. In essence this makes buying only Dark Oranges the most cost effective way to upgrade. That is, if you can wait that long. An effective way to accomplish that would be to focus just on two or three weapon-types you mainly use and only buy the current available SDUs for these. After Dark Orange upgrades become available you buy the remaining ones.