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AT&T 3B computer systems included the 3B2, 3B5, 3B15, 3B20S, and 3B4000. These computers were named after the successful 3B20D. The 3B20S (simplex) ran using the UNIX operating system and was developed at Bell Labs and produced by WECo in 1982 for the general purpose internal Bell System use, and later the mini-computer market.
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syscall(2) [bsd man page]

SYSCALL(2)							System Calls Manual							SYSCALL(2)

NAME
syscall - indirect system call SYNOPSIS
#include <syscall.h> syscall(number, arg, ...) (VAX-11) DESCRIPTION
Syscall performs the system call whose assembly language interface has the specified number, register arguments r0 and r1 and further argu- ments arg. Symbolic constants for system calls can be found in the header file <syscall.h>. The r0 value of the system call is returned. DIAGNOSTICS
When the C-bit is set, syscall returns -1 and sets the external variable errno (see intro(2)). BUGS
There is no way to simulate system calls such as pipe(2), which return values in register r1. 4th Berkeley Distribution April 16, 1986 SYSCALL(2)

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syscall(3UCB)					     SunOS/BSD Compatibility Library Functions					     syscall(3UCB)

NAME
syscall - indirect system call SYNOPSIS
/usr/ucb/cc [ flag ... ] file ... #include <sys/syscall.h> int syscall(number, arg, ...); DESCRIPTION
syscall() performs the function whose assembly language interface has the specified number, and arguments arg .... Symbolic constants for functions can be found in the header <sys/syscall.h>. RETURN VALUES
On error syscall() returns -1 and sets the external variable errno (see intro(2)). FILES
<sys/syscall.h> SEE ALSO
intro(2), pipe(2) NOTES
Use of these interfaces should be restricted to only applications written on BSD platforms. Use of these interfaces with any of the system libraries or in multi-thread applications is unsupported. WARNINGS
There is no way to use syscall() to call functions such as pipe(2) which return values that do not fit into one hardware register. Since many system calls are implemented as library wrappers around traps to the kernel, these calls may not behave as documented when called from syscall(), which bypasses these wrappers. For these reasons, using syscall() is not recommended. SunOS 5.10 22 Jan 1993 syscall(3UCB)

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