HP 9845B - Introduction
The HP-9845B was powerfull desktop graphics calculator with enhanced HP Basic, and it was the first computer from Hewlett Packard to "look" like a modern PC, with
a 12" monitor, two tape cartridge drives, thermal printer and keyboard all in one unit.
The original model, 9845A was introduced in April 1978. It has development name "Qwert" and only 16kB of RAM and one cartridge unit. The 9845s family were available in a
bewildering array of model numbers, options, packages, performance models and displays. In 1979 HP added the 9845S model. The "S" model had 64k of RAM, two cartridge units,
a built in full page printer and a graphics capability. Both models, "A" and "S", were replaced by the 9845B (code name "Galleon") and 9845T in year1980. The 9845C model with
colour monitor was introduced later, in the December 1980. The 9845s were 3rd generation of HP calculators and featured all of advances of the 9825 and 9835
included the same live keyboard, high speed tape drive, an extended number range and all of the interfacing capability of the 9835 such as buffered I/O, DMA, fast read/write,
15 levels of priority interrupts and built in I/O drivers. A second tape drive and a built in full page thermal printer were optional.
The 9845s use two nearly identical CPUs. One was called the LPU (Language Processing Unit) and the other called the PPU (Peripheral Processing Unit). The LPU handles the
BASIC interpreter and the PPU handles all of the system I/O. There was a 'high speed language processor option' that replaced the language processor with 3 boards stuffed with
AMD2900-series.
All of the HPL and BASIC language machines used interpreters and HP found that in most programs the machines spent 80% of their time in the interpreter. Therefore HP rewrote
most of the BASIC language interpreter in microcode. The microcode was 2K words with 56 bits wide.
The 9845B has four I/O slots in the rear of the case and two slide out ROM drawers into both sides of the machine. Each drawer could hold eight ROMs. Many of the ROMs had
to go into a specific drawer and slot. Therefore the left hand drawer was color coded green and the right hand drawer was color coded black. The slots were identified with
one of three symbols. The ROMs that had to go into a specific drawer or slot were color coded and marked with matching symbols. While the 9845A housed all of its ROMs in
the ROM drawers, the 9845B has system ROM inside the machine, out of the drawers.
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