When you think of the San Francisco 49ers, the first thought that comes to players and coaches minds is defense.

"Explosive players," said Packers Offensive Line Coach James Campen Thursday describing the Niners. 

"The first thing that you see out of their defensive front and their rush is that they are relentless. They keep coming, they keep coming, they keep coming. "

Last season San Francisco ranked fourth in the NFL in total defense.  They also finished fourth in the NFC in sacks and second in interceptions.  The 49ers also return all 11 starters, a rarity in the free agent era.

"That front seven, they get after the quarterback and they can stop the run," says WR Greg Jennings. 

"Their defensive backs aren't covering for a long time because the quarterback doesn't have too long to hold on to the ball."

Packers QB Aaron Rodgers pointed out the speed and tackling ability of the opposition's defense.

"As a quarterback that likes to move around I think that is definitely on my mind," Rodgers says. 

"It's probably not going to be me getting out in the open, making a move and trying to out-run somebody.  It's me getting out looking to make a play throwing the football."

San Francisco was led a year ago by their defense and eighth-ranked running game on offense.  The unknown in 2012 is how the additions of wide receivers Mario Manningham and Randy Moss will impact the 49ers passing game.

"Randy Moss is definitely a special player," says Head Coach Mike McCarthy. 

"He's played a long time, very productive.  Haven't really seen him this preseason so I don't really have a strong opinion on where he is today.   He's a unique talent and you definitely have to be aware when he is on the field."

"They are very balanced with running the ball as well as throwing the ball," says safety Morgan Burnett. 

"They have a good quarterback (Alex Smith) back there.  Plus they have two good tight ends in Vernon Davis and Delanie Walker so they have a great offense."

The Packers know they have their hands full with the 49ers offense and defense, but that doesn't mean the team is going to change it's identity in Sunday's opener.

"We are trying to attack them, bottom line," says Jennings.  "We are going to do what we do best, and hopefully we can execute.