Since its inception half a century ago, DRAM has required dynamic/active refresh operations that block read requests and decrease performance. We propose refreshing DRAM in the background without stalling read accesses to refreshing memory blocks, similar to the static/background refresh in SRAM. Our proposed Nonblocking Refresh works by refreshing a portion of the data in a memory block at a time and uses redundant data, such as Reed-Solomon codes, in the block to compute the block's refreshing/unreadable data to satisfy read requests. For proof of concept, we apply Nonblocking Refresh to server memory systems, where every memory block already contains redundant data to provide hardware failure protection. In this context, Nonblocking Refresh can utilize server memory system's existing per-block redundant data in the common-case when there are no hardware faults to correct, without requiring any dedicated redundant data of its own. Our evaluations show that on average across five server memory systems with different redundancy and failure protection strengths, Nonblocking Refresh improves performance by 16.2% and 30.3% for 16gb and 32gb DRAM chips, respectively. / Master of Science / Main memory is an essential component of computers, which stores data being actively used. The dominant type of computer main memory is Dynamic Random Access Memory (DRAM). DRAM is divided into thousands of memory cells. Each cell stores a single bit of data as a charge on a capacitor. Charges may leak over time, causing the data stored to be lost. To maintain the data stored in memory, DRAM must periodically restore charges held by memory cells through an operation known as memory refresh. Refresh operations decrease system performance because they stall read requests to refreshing memory blocks. A memory block refers to the unit of data transferred per memory request. Conventional memory systems refresh all the data within the block at a time, therefore the entire memory block is inaccessible while it is being refreshed. Our proposed Nonblocking Refresh reduces the amount of data in a memory block which is inaccessible due to refresh by refreshing only a portion the memory block at a time. To satisfy read requests, the block’s refreshing/inaccessible data is computed using redundant data. Nonblocking Refresh improves DRAM performance by refreshing DRAM in the background without stalling read accesses to refreshing memory blocks. For proof of concept, we apply Nonblocking Refresh to server memory systems, where every memory block already contains redundant data to provide hardware failure protection. In this context, Nonblocking Refresh can utilize server memory system’s existing redundant data to improve performance, without adding additional redundancy overhead. Our evaluations show that on average across five server memory systems with different redundancy and failure protection strengths, Nonblocking Refresh improves performance by 16%-30%.