Editing Pyramid Technology (section)

===90x===
The first Pyramid Technology series of minicomputers was released in August 1983<ref>{{cite magazine |url=https://books.google.com/books?id=soGti0kvtgwC&dq=Pyramid+90x+computer.&pg=RA1-PA73| title=Supports Up to 128 Users Pyramid 32-Bit Mini Designed for Unix|page=73|magazine=Computerworld| date=15 August 1983 |quote=...has unwrapped a 32-bit, ...minicomputer...Pyramid 90x... |first= |last= |volume=XVII |issue=33}}</ref><ref>[https://books.google.com/books?id=_itgx7IkelMC&dq=Pyramid+Technology+Corp.%2C+Mountain+View%2C+CA&pg=RA1-PA184 Position advert: Pyramid Systems Support Specialist], Page 184, Computerworld, 12 Sep 1983, ''Pyramid Technology Corporation, a new Mountain View, California company focused on ... has recently announced its first product: the Pyramid 90x computer.''</ref> as the 90x superminicomputer, which used their custom [[32-bit]] [[scalar processor]] running at 8&nbsp;MHz.

Although the architecture was marketed as a [[RISC]] machine, it was actually [[microcode|microprogrammed]]. It used a "sliding window" [[processor register|register]] model based on the [[Berkeley RISC]] processor, but memory access instructions had complex operation modes that could require many cycles to run. Many register-to-register scalar instructions were executed in a single machine cycle. Initially, [[floating point]] instructions were executed totally in microcode, although an optional [[floating point unit]] on a separate circuit board was released later. Microprogramming also allowed other non-RISC luxuries such as block move instructions.

Programs had access to 64 registers, and many instructions were triadic. Sixteen registers (registers 48 to 63) were referred to as "global registers" and they correspond to the registers of a typical CPU, in that they are static and always visible. The other 48 registers were actually the top of the [[subroutine]] stack. Thirty-two of them (0–31) were local registers for the current subroutine, and registers 32–47 were used to pass up to 16 parameters to the next subroutine called. During a subroutine call, the register stack moved up 32 words, so the caller's registers 32–47 became the called subroutine's registers 0–15. The return instruction dropped the stack by 32 words so return parameters would be visible to the caller in registers 32–47. The stack cache held 16 levels in the CPU and [[stack overflow]] and [[underflow]] was automatically handled by the microcode of the CPU. The programming model had two stacks, one for the register stack, and one for subroutine local variables. One grew up from a designated address in the middle of the address space, and the other grew down from the top of the user mode address space.

The 90x could accommodate four memory boards, initially holding 1&nbsp;MB each. This was considered to be a lot of memory at the time, but the RISC-like architecture resulted in bigger programs than earlier architectures so most machines were sold with the memory slots full. Fortunately, the 1&nbsp;MB memory boards had RAM in sockets, so they could be upgraded to 4&nbsp;MB units when bigger dynamic RAM devices became available shortly after the 90x's initial release.

The 90x competed with the [[Digital Equipment Corporation]] (DEC) [[VAX]] 11/780 which was the preferred platform for running UNIX in the early 1980s. The 90x processor benchmarked at roughly twice the speed of the VAX, and sold for about half the price. Pyramid was indirectly assisted by DEC's reluctance to sell VAX machines without the [[OpenVMS|VMS]] [[operating system]], for which they charged a considerable amount of money. Many universities wanted to run UNIX rather than VMS, so Pyramid's higher performance and lower price, coupled with artificial delivery delays or surcharges from DEC, helped them to make the risky decision to buy from a new manufacturer.

One of the 90x's biggest advantages over the competition was its asynchronous [[serial port]] controller (the ITS or Intelligent Terminal Server) based on a [[16-bit]] [[bit-slice]] processor. The ITS interfaced to 16 serial ports, and it could run them at very high speeds, using DMA to feed from [[Daisy chain (electrical engineering)|daisy-chained]] output data blocks. A machine could have many ITSs installed, each one with its own I/O processor. Other machines at the time (including the 11/780) required CPU intervention every few bytes for interactive users, which added significantly to the system component of the CPU [[Load (computing)|load]]. As a result, the 90x scored very well on benchmarks with a realistic amount of serial I/O.

The disk and magnetic tape controllers were actually 16-bit third-party [[Multibus]] controllers fitted into a socket in a U-shaped bus-adapter board.

Most early systems were delivered with the 470&nbsp;MB [[Fujitsu Eagle]] disk drive and a slot-loading reel-to-reel streaming tape drive.

Just like the VAX 11/780, which had a [[PDP-11|PDP-11/03]] with a {{convert|8|in|adj=on}} [[floppy disk]] as its console processor, the 90x had a "System Support Processor", based on a [[Motorola 68000]], that loaded the microcode from an {{convert|5.25|in|adj=on}} floppy disk when the system was started. It was also able to run a suite of diagnostics over the system. It had a [[modem]] which allowed remote analysis by the manufacturer. The software run by the administrative processor was initially called the Totally Unrealistic Remote Diagnostic. This name was changed some years later.

A minimal system was delivered in a single {{convert|19|in|adj=on}} rack about {{convert|60|in|adj=on}} high with the card cage in the bottom, the disk drive in the middle, the tape drive above it, then the 2 inch high control panel with a floppy disk drive and ignition key on the top. This was considered very compact at the time. At least one machine in Australia spend six months installed in a retired outdoor lavatory with an air-conditioner replacing the [[louvered window]] and the system console terminal sitting on top of the cabinet. Administration tasks were performed al-fresco. The only indicator on the control panel was an 8 segment bar graph LED display that displayed average CPU usage when the machine was running and a "[[Cylon (Battlestar Galactica)|Cylon]] Eye" pattern when the machine stopped unexpectedly. The machine was low enough that the console (a monochrome asynchronous terminal) could rest on top.