Despite these remedies, the workstations offering RISC iX were regarded as being hampered by the memory management unit (MMU) using 32 KB pages. The hardware supporting RISC iX also did not have direct memory access capabilities for disk operations, meaning that the CPU would spend time servicing interrupts related to disk transfers resulting in "a definite reduction in, but not a complete loss of, available CPU power during disc transfers". However, by reducing the amount of data being fetched, the executable decompression technique did reduce CPU involvement in performing disc transfers, albeit at the expense of incurring CPU usage in the decompression of retrieved pages. Positive outcomes of the decompression scheme also included reduced loading on storage devices, of importance for networked storage, and generally improved disc transfer performance. Distribution RISC iX was either supplied preinstalled on new computer hardware or was installed onsite from a portable tape drive by Granada Microcare, who would take the installation tape away with them. Upgrades to RISC iX 1.2 from earlier versions started at £349 for R140 machines, and new installations for A400-series machines started at £999. Installations required 100 MB of space on suitable hard drive or network storage, with hard drive and SCSI card bundles being offered from £1699 for R140 machines and from £2326 for A400-series machines. Once installed a backup of the core operating system to three floppy disks was possible, allowing future reinstallation through the use of remote filesystems or backup media to transfer files to a machine. Supported hardware According to documentation concerning RISC iX 1.2 availability, the operating system could be used on the R140, R225 and R260, being pre-installed on the R260, accessible via a fileserver (such as an R260) on the R225, and as an upgrade from RISC iX 1.15 or earlier on the R140. The A540, being practically identical to the R260, could support RISC iX as delivered, whereas A400-series machines required an Acorn SCSI card, with older A400-series machines also needing a memory controller upgrade and "all the appropriate field change orders" to have been performed. A300-series and the A3000 machines were not supported. RISC iX is not compatible with later Archimedes machines. Machines Several machines were designed specifically to run RISC iX. M4 An unreleased machine, built internally by Acorn for the development of RISC iX. Reputedly only three were built and one of them has subsequently been destroyed. All known