Editing IBM PCjr (section)

=== Processor ===
Like the IBM PC, the PCjr uses an [[Intel 8088]] clocked at 4.77&nbsp;MHz.

Despite using the same CPU and clock speed, performance is often inferior to the PC, because access to system RAM is delayed by [[wait state]]s added by the Video Gate Array to synchronize shared access to RAM between the CPU and the video hardware. IBM claimed that an average of two wait states are added, but the designers of the Tandy 1000, a clone of the PCjr, claimed that six was a more accurate figure.<ref name="vose198412">{{Cite magazine|last=Vose|first=G. Michael|date=December 1984|title=The Tandy 1000|url=https://archive.org/stream/byte-magazine-1984-12/1984_12_BYTE_09-13_Communications#page/n99/mode/2up|magazine=BYTE|pages=98–104}}</ref>

This delay only applies to software resident in the first 64 KB or 128 KB of RAM inside the system unit itself, and not to programs or data located in ROM - including software on ROM cartridges plugged into the front of the PCjr - or in additional RAM in a sidecar attachment. Under these circumstances the PCjr should run at full speed. The most common instances in which this maximum speed would be achieved are when running games or productivity applications from ROM cartridges. In fact, because the PCjr video subsystem continuously refreshes the system internal DRAM transparently, without disturbing the CPU, programs running from ROM on the PCjr may actually run slightly faster on the PCjr than on an IBM PC or XT.