DDR4 SDRAM computer buses have migrated towards replacing parallel buses with serial buses, for example by the evolution of Serial ATA replacing Parallel ATA, PCI Express replacing PCI, and serial ports replacing parallel ports. In general, serial buses are easier to scale up and have fewer wires/traces, making circuit boards using them easier to design. In the longer term, experts speculate that non-volatile RAM types like PCM (phase-change memory), RRAM (resistive random-access memory), or MRAM (magnetoresistive random-access memory) could replace DDR4 SDRAM and its successors. GDDR5 SGRAM is a graphics type of DDR3 synchronous graphics RAM, which was introduced before DDR4, and
IPAQ (desktop computer) to the RAM limit of the Intel 815 series chipset, the BIOS in the iPAQ prevents the system from booting if there is more than 512 MB installed, instructing the user to decrease the amount of RAM in the system to no more than 512 MB. The first version came in two different models, "Legacy free" which had no parallel, serial, or PS/2 ports and instead 3 additional USB ports on the back; and the traditional one which included the parallel, serial, and PS/2 ports but only had USB ports on the front. The second version had different styling and