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Bolt Beranek and Newman Inc.
Without recourse to expensive additional peripherals, the
assembly facilities on the DDP-516 are inadequate for a large
program. (For example, a listing of the IMP program would require
approximately 20 hours of Teletype output). Therefore,
BBN uses other locally available facilities to assist in the
assembly process. Specifically, a PDP-lD text editor is used to
compose and edit the programs, which are stored on a large random
access file. The file is then used as a source for a PDP-lD
assembly program which assembles the IMP system, producing both
object machine code and program listings.
The PDP-lD as a Host on the network provides two additional
debugging aids. Core images of the current IMP system are created
and maintained on the PDP-lD mass storage directly from assembled
object code. 1tlhen requested by the IMPVER program, an IMP's debug
program dumps some or all of its core to the PDP-lD, where
it is verified against the core image and discrepancies are
typed out. If diagnostic or corrective patches are required in
a part or all of the network, it is made up as a small IMP assembly,
and the PDP-lD program BRODCAST can quickly send the patch
to the required IMP(s).
Additionally, when an IMP running a very distant Host requires
a fresh copy of its very distant Host module (which is not present,
for example, when an IHP reloads from a neighbor), the PDP-lD's
VDHLOAD program extracts this module from the IMP system binary
files, broadcasts it to the IMP in question, and starts the module.
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