If this happens, it will default to a gray background with brown text. In CP/M mode, it is possible to run MBASIC, Microsoft's release of BASIC-80 for CP/M. Compared with the native mode BASIC 7.0, MBASIC is terse and limited in its capabilities, requiring the use of terminal-style key combinations to edit program lines or move the text cursor and lacking any sound or graphics features. Although MBASIC has mathematical and calculation features that BASIC 7.0 lacks such as integer and double precision variable support, any speed advantage gained by the use of integer variables is rendered moot by the extremely slow performance of the computer in CP/M mode. Moreover, Commodore BASIC has 40-bit floating point which serves as a middle ground between MBASIC's 32-bit floating point and 64-bit double precision variables. MBASIC also offers only 34k of free program space against BASIC 7.0's approximately 90k. Other CP/M software such as Wordstar and Supercalc will also be significantly outperformed by native mode C128 equivalents like PaperClip, which also have an easier to use interface. The CP/M CBIOS (the part of CP/M that interfaces with the hardware) does not directly interface with the hardware like on most CP/M implementations, rather it calls the kernal routines for interrupt handing and I/O—when the kernal needs to be used, the Z80 uses routines at - to pass parameter data to the 8502, which is then activated and the Z80 deactivated. After the kernal routine is finished executing, control is passed back to the Z80. It was reported that the programmer in charge of porting CP/M to the C128 had intended to have the CBIOS interface with the hardware directly in Z80 machine language, but had great difficulty with the VDU chips as they were prone to overheating and self-destructing. The VDU also underwent numerous hardware revisions while the C128 was in development and the CP/M programmer was unable to get his code working properly, so the C128 engineering team requested instead that he simply rewrite the CBIOS to pass function calls to the 8502. CP/M mode is very different from the operating environments familiar to Commodore users. While Commodore DOS is built into the ROM of Commodore disk drives and is usually accessed through BASIC, CP/M requires the use of a boot diskette and requires entry of terse commands inherited from minicomputer platforms. CP/M programs tend to lack the user-friendly nature of most Commodore