reentrancy on a per-section basis. RSECT was previously "undocumented and inconsistently implemented in Assembler H." HLASM is the current assembler for IBM mainframe systems as of 2012. Specialized versions IBM System/360 Model 44 PS assembler The IBM System/360 Model 44 Programming System Assembler processes a language that is a "selected subset" of OS/360 and DOS/360 assembler language. It has no support for storage-to-storage (SS) instructions or the convert to binary (CVB), convert to decimal (CVD), read direct (RDD) and write direct (WRD) instructions. It does include four instructions unique to the Model 44: Change Priority Mask (CHPM), Load PSW Special (LPSX), Read Direct Word (RDDW), and Write Direct Word (WRDW). It also includes directives to update the source program, a function performed by utility programs in other systems (SKPTO, REWND, NUM, OMIT and ENDUP). It provides named common and implicitly defined &SETA symbols, but has some restrictions as well. IBM System/360 TSS assembler The assembler for the System/360 Model 67 Time Sharing System has a number of differences in directives to support unique TSS features. The PSECT directive generates a Prototype Control Section containing relocatable address constants and modifiable data used by the program. Non-IBM assemblers There have been several IBM-compatible assemblers for special environments. The Univac 90/60, 90/70 and 90/80 series from Unisys was designed to accept IBM-format assembler, as the machine series was a workalike to the S/360 and S/370. The Fujitsu BS2000 series was also built as a 370 workalike from the same resource as Univac, and is still in use in some parts of Europe. Dignus LLC Systems/ASM is an HLASM-compatible assembler that can run natively on IBM systems or as a cross-assembler. Freeware PC/370, written by Don Higgins, was later purchased by Micro Focus. z390 is an assembler and System 390 emulator also written by Don Higgins and is programmed in Java. It is open source and available from http://www.z390.org/ Penn State University authored a package called ASSIST, which includes a System 370 assembler and interpreter. Tachyon Software LLC markets the Tachyon Assembler Workbench which runs on Windows, Linux/x86, Linux for S/390 and zSeries, AIX and Solaris. GNU Assembler (gas) is part of the GNU Compiler Collection (gcc) for Linux on OS/390 and IBM Z. This assembler has a unique syntax that is incompatible with other assemblers for IBM architectures. See also IBM System/360 Assembly language ASSIST assembler PC-based IBM-compatible mainframes – list of compatible