Students who do not have graduate status cannot enroll in 6.853 this year. The good news is that it will be offered next year, so you can take it next year. If you are looking for an interesting subject to take that is related to systems you might consider 6.857 (network security) or 6.313 (contemporary computer architecture).
The following students are enrolled in 6.853 this term:
The following students are on a waiting list:
If you are not on any of these two lists, then you are not enrolled in 6.853.
If you are on the list but you are not sure whether you want to take 6.853, please make up your mind soon; there are other students who would like to take your place.