360 Assembly/360 Family

There are a number of different computers that used the 360 machine architecture. These include

• IBM 360 series, the Univac 90/60 and 90/70 series, the RCA Spectra 70 series, the English Electric System 4 series, the Siemens 7.7xx, 7.5xx and H60/H90/H120 series.
• The IBM 370 and Fujitsu B2000 are, and Univac 90/80 were an enhanced version of the 360 series.
• Smaller versions of the IBM 370 were also released as the 43xx series.
• Larger versions of the 370 were released as the 30xx series.
• An intermediate upgrade to the 370 was released as ESA/390.
• The z/System is similar to the 370/390 series except that the z/System is a 64-bit machine while the IBM 370 and predecessors are 32-bit machines.

In software emulation there are some proprietary applications and three open source ones:

• The Z390 portable assembler provides an Assembler-H (high level) equivalent assembler, Cobol compiler, linkage editor and execution environment for programs written in assembler or Cobol
• The Hercules system provides an emulation of either System 370 or z/System hardware satisfactorily enough to run IBM-based operating systems and user programs running within those systems.
• QEMU is an open source emulator for many platforms, including z/Architecture (which it calls s390x). It only supports running Linux as a guest operating system.

The 360 architecture is a big endian machine (as opposed to the typical Intel or AMD x86 processor, which is little endian), in that values are stored high to low. For example, the 16-bit value 256 would be stored (in hex) as 0100 on a 360-series machine, but be stored as 0001 on an Intel Pentium. The number 1, on the other hand, if rendered as a 16-bit number, would be stored (in hex) as 0001 on a 360, and 0100 on a Pentium. Also, the standard character set on the 360/370/Z-System is EBCDIC, while the Pentium/X86/X64 uses ASCII (and Unicode, a superset of ASCII). This can cause a number of headaches in conversion of binary data files - or even text files - from one machine to another.

The bit order for bytes, half words, words, double words, and quad words, proceeds from left to right, with bit 0 being the most significant bit, and bit 7 in byte, bit 15 in a halfword, it 31 in a word, or bit 63 in a doubleword, is the least significant byte. Here is the correlation of bits, bytes, halfworrds. words and doublewords:

Organization of Bits and Bytes

Doubleword 0
Word 0																																	Word 1
Halfword 0																	Halfword 1																Halfword 2																Halfword 3
byte 0									byte 1								byte 2								byte 3								byte 4								byte 5								byte 6								byte 7
Bit #	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
or	Doubleword 0
Bit #	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48	49	50	51	52	53	54	55	56	57	58	59	60	61	62	63