Software packages which use windows have become increasingly popular in the last two years. Their popularity derives from the belief that windows will improve productivity by decreasing task completion time. However, two studies (Silver, 1985 and Davies, Bury and Darnell, 1985) have found this not to be the case. In fact, one of the studies (Davies at al., 1985) found that task completion time was increased when using windows. It is thought that performance using window systems is a function of the number of responses required to be executed as well as the amount of information which must be found and used to complete a task. The purpose of the present study was to determine under what conditions, in terms of memory load and task complexity, performance using windows and non-window strategies differed. Forty-eight subjects were placed in one of four environments and each performed six editing tasks which varied on complexity and memory load level. Human performance in one windowed environment was compared to three non-window strategies. These three strategies, note-taking, memorizing, or switching between files, were included to allow comparisons in terms of working memory and number and types of responses executed. The tasks required subjects to locate information from a supplementary file and type it into a main file. The three memory load levels which were used required subjects to find either 2, 4 or 8 pieces of information. The two complexity levels referred to the placement of needed information in the supplementary file; whether or not information was located in close proximity to other needed information. Results indicated that it made little difference which system was used in the low memory load condition. However, as memory load increased, more subjects were found to make errors in the non-window conditions. More responses were executed in the Switch condition than in the Window or Memorization conditions in the high memory load condition. Mental workload was also found to be higher in the Memorization and Switch conditions than in the Window and Notes conditions as memory load increased. Nevertheless, there was no significant interaction for task completion times between Memory Load and Environment. This was thought to be due to a failure to adequately load working memory as well as a failure of a test of verbal and spatial ability to account for individual differences. It was concluded that the benefits of windows are not apparent until one°s working memory capacity is exceeded. As memory load increases beyond this point, it is thought that memorization will quickly become an inefficient strategy due to limitations of memory capacity. As memory load continues to increase, a switching strategy should become inefficient due to limitations of both memory and response capacities. A strategy of note taking should not become inefficient until a large memory load is placed upon the user. This is because note taking is a well learned uncomplicated response. The benefits of windows include a reduction in the number of responses, errors, and mental workload due to their ability to reduce the amount of mental resources required by providing the user with a very efficient and accurate memory aid. / Ph. D.