There have been a lot of developments in microprocessors since the 286 chip. The 286 CPU are no longer sold and are very rarely found in commercial use today because of its running speed, which is between 10MHz to 20MHz. This processor has a 24-bit address bus, and is able to address up to 16 million different address locations. It also has two operating modes, which are real mode and protected mode. The real mode is basically for normal DOS operations and it uses only 8086 code (8086 was the previous CPU). When it was in protected mode the CPU is able to access beyond the 1mb address limit and employed its added features, which were intended for multi-tasking operations such as Windows, but this CPU is not powerful enough to carry out these multi-tasking operations. The 286 came with a bus width of 16-bit internal, 24-bit address, and 16-bit external, with an external speed of between 6MHz - 25MHz, and an internal speed of between 6MHz - 25MHz. The next CPU was the 386, this is also no longer produced it had a slightly faster running speeds which are between 16MHz to 40MHz. This CPU could carry out effective multi tasking operations. It also had a substantial improvement in both memory management and it had an enlarged instruction set. It is also the minimum CPU for running windows. It came in two types the 386 SX and the 386 DX. The SX had a 32-bit internal data path but it only had a 16-bit path between the CPU and the computer memory. The DX on the other hand had a 32-bit data bus between the CPU and the memory chips allowing larger data transfers so it had faster through put. It also was able to use external cache memory, usually about 64k, which also improved performance. The 386 came in two different types they both had a internal bus width of 32 bit, the SX had a address bus width of 24 bit, and a external bus width of 16 bit, its internal and external speed was between 16MHz - 33MHz.