Unlike the 9810, 9820 and 9830 series, the 9825, 9835 and 9845 were not all released at the same time. Also unlike the earlier series, the 98x5 series shared many common interfaces and peripherals.
AKA System 35. Both the 9835 A (picture) and B models were introduced in the 1979 HP catalog but were not available until May of that year. Their development code name was "Raven". The 9835 was released after the HP 9845 and was essentaully a baby 9845B. It had a single processor, that switched between being an LPU and PPU. Interestingly, most programs saw little performance difference. The 9835s were another third generation machine and featured all of advances of the 9825s included the same live keyboard, high speed tape drive and an extended number range plus they added an impressive range of interfacing capability including buffered I/O, DMA, fast read/write, 15 levels of priority interrupts and built in I/O drivers. The 9835s came standard with 64K bytes of read/write memory and 112K bytes of read/only memory. The read/write memory was expandable in increments of 64K to the full 256K bytes. Even though a machine might have 64k of read/write memory, the operating system would use a portion of it so only 49,962 bytes were available on a 9835A and 45,854 bytes were available on a 9835B. The option ROMs also used some of the read/write memory so the amount of memory available could even be less than that listed. A second tape drive was listed as being optional but I think that was a typographical error since there is no room for it in the machine. A sixteen character printer was optional. The 9835s featured HP's Enhanced BASIC. Enhanced BASIC was compatible with ANSI BASIC and featured FORTRAN-like capabilities such as subprograms, multicharacter identifiers, large-scale array operations, line labels and flexible output formatting. The 9835s could be programmed in either BASIC or Assembly Language. Assembly Language offered speed increases of up to 100 times in some applications. They also featured four ROM slots in the front and three I/O slots in the rear of the case.
The ROMs used in the 9835 are rather unusual. The ROM carriers look exactly like the ROMs for the HP 9825 but without labels. But instead of only holding one ROM, each carrier has sockets for four ROMs. The individual ROMs are small square boxes similar to those used in the HP 85. The 9835 ROMs come in sets of 1, 2 or 4 individual ROMs and the ROMs can be mounted in any order in the carrier or in any position in the 9835. The fourteen operating system ROMs are similarly mounted in a pull out drawer on the left side of the 9835. Flash! I've just learned that one collector has a 9835 with ROM drawers that hold six ROMs each instead of four. That's something that I haven't heard of before.
The 9835A and B models were very different. Take a look at this "Overview" from the HP 9835 Preview manual. The 9835A model featured a CRT monitor on top on the machine but the 9835B featured a 32 character LED display like that used in the 9825. The monitor used on the 9835A displayed 24 lines with 80 characters per line. The CRT measured 12 in. diagonally and had a dual raster-scan, P31 green phosphor screen with adjustable brightness. The color, contrast, size and brilliance were chosen for maximum ease of viewing. It also featured inverse video, blinking and underlining that could be used in any combination to highlight selected areas on the screen. Even though the display used on the 9835B only showed 32 characters, the 9835 would accept input lines of up to 160 characters and the display could be scrolled left and right to display any portion the 160 character line.
