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Document:	itsmanpg19
Order Number:	XX-D9D3F-B2
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Pages:	1
Original Filename:	itsmanpg19.pdf

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L
ITS 1.5 Reference Manua1

Paee L9

2. The General Transaction of Input-Output
See also section 0.2.2.

2.1 Philosophy and. 0rganization

Standard ITS input-output has been organized r,rith such goals r*s

synbolic d.evice independ.ence, no required buffering in tne user,s
core image, sinple unit (character, word., vid.isector point, etc.)
node transfers available along with block at a time transfers chich

greatly reduce overhead by red.ucing the number of systen calls, iach
troceC.ure has associated with it 20 input-output channels (but see

section 2.6). nach of these channels stores information for a

transfer in one direction and. mode between the program and a file on
a. device with which the charrnel vias associated. by the execution of a

.0PEN [Sec 2.2]. Items are then transmitted over ihe shannel by the

execution of .I0T's [Sec 2.S]. This association may be terminated by

a .CLOSX [Sec 2.?.1) or another .QPE|'I on the same channel.
i,tost data transfers directly to or from symbolic IIS devices
[App C] are effected. to or from huff'ers in system menory. In the

case of major file devices (DSK and ilTn) these buffers are

dynamically allocated from free memory by ITS LSec 4.3J. The

additional overhead required to transmit data between a user's core
iuaqe and the system's buffer as comlared with a system having direct