The program status word[a] (PSW) is a register that performs the function of a status register and program counter, and sometimes more. The term is also applied to a copy of the PSW in storage. This article only discusses the PSW in the IBM System/360[1] and its successors,[2][3][4][5][6] and follows the IBM convention of numbering bits starting with 0 as the leftmost (most significant) bit.
Although certain fields within the PSW may be tested or set by using non-privileged instructions, testing or setting the remaining fields may only be accomplished by using privileged instructions.
Contained within the PSW are the two bit condition code, representing zero, positive, negative, overflow, and similar flags of other architectures' status registers. Conditional branch instructions test this encoded as a four bit value, with each bit representing a test of one of the four condition code values, 23 + 22 + 21 + 20. (Since IBM uses big-endian bit numbering, mask value 8 selects code 0, mask value 4 selects code 1, mask value 2 selects code 2, and mask value 1 selects code 3.)
In the early instances of the architecture (System/360 and early System/370), the instruction address was 24[b] bits; in later instances (XA/370), the instruction address was 31 bits plus a mode bit (24 bit addressing mode if zero; 31 bit addressing mode if one) for a total of 32 bits.
In the present instances of the architecture (z/Architecture), the instruction address is 64 bits and the PSW itself is 128 bits.
The PSW may be loaded by the LOAD PSW instruction (LPSW or LPSWE). Its contents may be examined with the Extract PSW instruction (EPSW).
^However, a 360/67[7] equipped with the Extended Dynamic Address Translation[8]
feature has a 32-bit mode selected by bit 4 of the PSW[9] in Extended PSW mode[8] (Control Register 6, bit 8[10]).
^Despite the name, the 350/20 does not adhere to the S/360 architecture.
^Bit 22 is renamed as HFP exponent underflow in ESA/390
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction