video hardware supporting block graphics characters, and these were accessible to assembler programmers and BASIC programmers using the CHR$ command. The Model 4 could display 640 by 240 pixel graphics with an optional high resolution board. Derivatives A number of CP/M-80 derivatives existed in the former Eastern Bloc under various names, including SCP (), SCP/M, CP/A, CP/J, CP/KC, CP/KSOB, CP/L, CP/Z, MICRODOS, BCU880, ZOAZ, OS/M, TOS/M, ZSDOS, M/OS, COS-PSA, DOS-PSA, CSOC, CSOS, CZ-CPM and others. There were also CP/M-86 derivatives named SCP1700, CP/K and K8918-OS. They were produced by the East German VEB Robotron and others. Legacy A number of behaviors exhibited by Microsoft Windows are a result of backward compatibility with MS-DOS, which in turn attempted some backward compatibility with CP/M. The drive letter and 8.3 filename conventions in MS-DOS (and early Windows versions) were originally adopted from CP/M. The wildcard matching characters used by Windows (? and *) are based on those of CP/M, as are the reserved filenames used to redirect output to a printer ("PRN:"), and the console ("CON:"). The drive names A and B were used to designate the two floppy disk drives that CP/M systems typically used; when hard drives appeared, they were designated C, which survived into MS-DOS as the C:\> command prompt. The control character ^Z marking the end of some text files can also be attributed to CP/M. Various commands in DOS were modelled after CP/M commands; some of them even carried the same name, like DIR, REN/RENAME, or TYPE (and ERA/ERASE in DR-DOS). File extensions like .TXT or .COM are still used to identify file types on many operating systems. In 1997 and 1998, Caldera released some CP/M 2.2 binaries and source code under an open source license, also allowing the redistribution and modification of further collected Digital Research files related to the CP/M and MP/M families through Tim Olmstead's "The Unofficial CP/M Web site" since 1997. After Olmstead's death on 12 September 2001, the distribution license was refreshed and expanded by Lineo, who had meanwhile become the owner of those Digital Research assets, on 19 October 2001. In October 2014, to mark the 40th anniversary of the first presentation of CP/M, the Computer History Museum released early source code versions of CP/M. , there are a number of active vintage, hobby and retro-computer people and groups, and some small commercial businesses, still developing and supporting computer platforms that use