An emulator uses code translation and recompilation to execute target computer system applications on a host computer system. Target application code is partitioned into target application code blocks, and related target application code blocks are combined into block groups and translated. Translated application code block groups are sized to comply with restrictions on branch instruction size. Upon selecting an application code block group for execution, a cache tag is used to determine if a corresponding translated code block group is available and valid. If not, the block group is translated and executed. Sequentially executed translated code blocks are located in adjacent portions of memory to improve performance when switching between translated code blocks. The emulator may use a link register of the host computer system to prefetch instructions and data from translated code blocks. The emulator also takes into account structural hazards in translating instructions.