A line of workstations and servers from Sun Microsystems that introduced Sun's own processor, the SPARC. Starting in 1987, with the introduction of the 4/260, until 1995, with the introduction of the Ultra 1 workstation, this was the main line of Sun.

The systems produced can be classified in a couple of ways. Firstly, their marketing names (4/260 or SPARCstation 2). Secondly, their kernel architecture (sun4, sun4m, sun4c, sun4d)

Initially Sun followed their previous style of naming that they had started with their Sun 2 series. For servers this consisted of 4 digits (i.e. 4/260), for workstation 3 digits (i.e. 4/65). The first digit in both indicated a major revision (which CPU they used, Sun 3 indicated 68020 or 68030, Sun 4 indicated SPARC processors). For workstations the last two digits indicated just about nothing (i.e a Sparcstation 2 (4/75) is not really faster or better than a Sparcstation IPX (4/50)). For servers it is different and one can discern some information from them. The first digit after the slash indicates which CPU board it uses (these being VME based machines). The second indicates which chassis the machine uses. The third only serves to differentiate between servers and workstations. So for instance the 4/470 and the 4/490 have the same performance, but differ only in their chassis (the 490 is a rack mount, the 470 is a very large tower that sits on the floor).

When the SPARCstation 1 (4/60) was introduced in 1989, Sun's marketing division marketed the machines with names instead of just numbers. But the number lived on in documentation, inside of the boot ROM, and inside Sun support. About halfway through the line they dropped the system entirely (around the introduction of the SPARCstation 10.

For the purposes of the operating system the machines were divided along "architectures". Mostly this indicated bus support and/or MMU issues. (the only exception is the 4/6x0 series which had all the buses (VME, Sbus, Mbus).

sun4, indicated a VME based machine with no sbus or mbus support. Generally these were fairly large machines (with the exception of the 4/110). Machines in this class 4/260, 4/110, 4/280, 4/330, 4/360, 4/370, 4/390, 4/470, 4/490.

sun4c, indicated the desktop machines (pizzabox or lunchbox) that had sbus, but no mbus. Machines in this class SPARCstation 1 (4/60), SPARCstation SLC (4/20), SPARCstation IPC (4/40), SPARCstation 1+ (4/65), SPARCstation 2 (4/75), SPARCstation ELC (4/25), SPARCstation IPX (4/50).

sun4m, indicated desktop machines with mbus and sbus, and a single server (the 4/6x0 series). Machines in this class SPARCserver 6x0MP (4/6x0), SPARCclassic (4/15), SPARCstation LX/ZX (4/30), SPARCstation Voyager, SPARCstation 10, SPARCstation 20, SPARCstation 5, SPARCstation 4.

sun4d, indicates a machine that used the XDbus to support a large number of SPARC CPU's in a SMP configuration Machines in this class SPARCcenter 2000, SPARCserver 1000.

In addition Sun considered their UltraSPARC machines to be sun4u, but they should really be in a class of their own.

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