Working memory (WM) deficiencies in patients with schizophrenia (PSZ) are thought to be caused by PFC dysfunction, but few research have looked at non-manipulated measures of WM storage. Storage capacity is more closely tied to the posterior parietal cortex (PPC) than the frontal cortex (PFC) in neurotypical people, suggesting that impairments in WM storage capacity in schizophrenia that are associated with widespread cognitive deficits may be related to neuronal activity in the PPC. While receiving fMRI, 37 PSZ and 37 matched healthy control volunteers of both sexes conducted a change detection test with varied set sizes. The assignment was created to emphasis WM storage while requiring minimal top-down management. BOLD activity correlated with the number of items kept in WM (K), as determined by task performance at a particular set size, according to whole-brain analyses. Independent of set size, K values predicted BOLD activity in the PPC, including the superior and inferior parietal lobules, intraparietal sulcus, and middle occipital gyrus, across groups. In the left PPC, whole-brain interaction analysis revealed that PSZ had much less K-dependent signal modulation than healthy control participants, a finding that could not be explained by a smaller K value range. The slope between K and PPC activation accounted for 43.4 percent of the variations in broad cognitive performance across groups. These findings suggest that PPC dysfunction is linked to WM storage abnormalities in PSZ and may play a role in schizophrenia's widespread cognitive deficiencies.