Editing DECstation (section)

==== DECstation 3100 and DECstation 2100 ====
[[File:DECstation 2100 (01).jpg|thumb|DECstation 2100]]
{|class="wikitable" style=text-align:center
|-
! style="width:100px;"|Model and codename
! style="width:215px;"|Processor
! style="width:140px;"|MHz
! style="width:150px;"|Introduced
! style="width:150px;"|Withdrawn
|-
|'''3100 "PMAX"'''
|R2000, R2010, R2020 chipset<ref name="PMIN-PMAX">[http://ftp.hp.com/pub/alphaserver/archive/specs/DS3100.ps.Z Workstation Systems Engineering: "''DECstation 3100 Desktop Workstation Functional Specification''", Revision 1.3, 28 August 1990, Digital Equipment Corporation]</ref> <!-- Note that this document describes both the DECstation 2100 and 3100 -->
|16.67&nbsp;MHz (60 ns)<ref name="PMIN-PMAX"/>
|11 January 1989<ref>{{cite news|url=https://www.nytimes.com/1989/01/11/business/company-news-8-desktop-computers-introduced-by-digital.html |first=John |last=Markoff |title=COMPANY NEWS; 8 Desktop Computers Introduced by Digital |newspaper=New York Times |date=11 January 1989 |url-access=limited}}</ref>
|?
|-
|'''2100 "PMIN"'''
|R2000, R2010, R2020 chipset<ref name="PMIN-PMAX"/>
|12.50&nbsp;MHz (80 ns)<ref>RISC Family Performance Summary, 2 April 1990, Digital Equipment Corporation</ref>
|11 July 1989 <!-- Unconfirmed -->
|?
|}

===== Processor =====

The DECstation 3100 and 2100 uses a [[R2000 microprocessor|R2000]] processor, a R2010 floating point coprocessor and four R2020 write buffers. The R2000 uses an external 64&nbsp;KB<ref>When used in the context of semiconductor memory, 1&nbsp;KB refers to 2<sup>10</sup> (1,024) bytes and 1&nbsp;MB refers to 2<sup>20</sup> (1,048,576) bytes</ref> direct-mapped instruction cache and a 64&nbsp;KB direct-mapped write-through data cache with a cache line size of four bytes.<ref name="PMIN-PMAX"/> Four R2020 implement a four-stage write buffer to improve performance by permitting the R2000 to write to its write-through data cache without stalling.

The R2000 microprocessor could be configured to run either in big-endian or little-endian mode. In the DECstation family, the decision was made to run little-endian to maintain compatibility with both the [[VAX]] family and the growing population of Intel-based PC's.

===== Memory =====
The DECstation 3100 and 2100's memory system contains both the [[dynamic random-access memory|DRAM]]-based system memory and [[video random-access memory|VRAM]]-based framebuffers. The amount of system memory supported is 4 to 24&nbsp;MB, organized into six physical memory banks. These systems has 12 [[SIMM]] slots that use 2&nbsp;MB SIMMs, with each SIMM containing 1,048,576 [[Word (computer architecture)|word]] × 18-bit DRAMs. The SIMMs are installed in pairs (in increments of 4&nbsp;MB) and the memory system is byte-parity protected. The monochrome framebuffer are implemented with a 256&nbsp;KB VFB01 SIMM and the color framebuffer, a 1&nbsp;MB VBF02 SIMM. If one of these framebuffer SIMMs are not present, the framebuffer cannot be used. The SIMM slots were rated for 25 removal and insertion cycles, with five being the recommended limit.

===== Graphics =====

Graphics capability was provided by two frame buffer modules, the monochrome and color frame buffer. The monochrome frame buffer supports 1-bit color and a resolution of 1024 × 864 pixels, while the color frame buffer supports 8-bit color and the same resolution as the monochrome frame buffer. Both frame buffers use the [[Brooktree]] Bt478 [[RAMDAC]] with three 256-entry, 8-bit color maps. The hardware cursor is generated by DC503 PCC (Programmable Cursor Chip), which can provide a 16 × 16 pixel, 2-bit color cursor. The color frame buffer has an 8-bit write mask, also known as a "planemask", used to select which pixels are to be updated. None of the framebuffers use all the memory provided by the frame buffer module, this being organized as 1024 × 1024 pixels, and thus only the uppermost 864 pixels are used for the display. Unused areas of the frame buffer memory may be used to store graphical structures such as fonts, although this was considered to offer "no performance advantage over main memory" and, in the context of the X server implemented by Digital, would have complicated the memory management involved.<ref name="dec_wrl_tn9">{{ cite tech report | url=https://archive.org/details/bitsavers_dectechrep_55398/mode/2up | title=Smart Code, Stupid Memory: A Fast X Server for a Dumb Color Frame Buffer | publisher=Digital Equipment Corporation | date=September 1989 | access-date=3 March 2022 | last1=McCormack | first1=Joel }}</ref> The frame buffers are not parity-protected, unlike the rest of the system memory. A DB15 male connector is used for video. The connector uses RS343A/RS170 compatible signals.

===== Ethernet and SCSI =====

These DECstations have onboard [[Ethernet|10 Mbit/s Ethernet]] provided by an [[AMD Lance Am7990|AMD 7990 LANCE]] (Local Area Network Controller for Ethernet) and an AMD 7992 SIA (Serial Interface Adapter), which implements the interface, a BNC ThinWire Ethernet connector. A 32 768 word × 16-bit (64&nbsp;KB) network buffer constructed out of SRAMs is provided to improve performance. A 32 word by 8-bit Ethernet Station Address ROM (ESAR) provides the [[MAC address]]. It is mounted in a DIP socket and is removable.

The 5&nbsp;MB/s single-ended SCSI interface is provided by a DC7061 SII [[gate array]] with a 64 K by 16-bit (128&nbsp;KB) SCSI buffer used to improve performance. The SCSI interface is connected to the internal 3.5 drive bays and an external port (HONDA68 male connector) to be connected to drive expansion boxes.

===== Other =====

These systems have four asynchronous serial lines that are provided by a DC7085 gate array. Of the four serial lines, only the third line has the required modem control signals to support a modem. A 4-pin MMJ connector is provided for the keyboard line, a 7-pin DIN connector for mouse line, and two 6-pin MMJ connectors for printer and modem lines. The real time clock is a Motorola MC146818, which also has 50 bytes of RAM for storing console configuration information, and the 256&nbsp;KB of ROM for storing boot-strap and self-test software is provided by two 128&nbsp;KB ROMs in DIP sockets.

===== Enclosure =====

The enclosure used by the DECstation 3100 and 2100 is identical to the enclosure used by the VAXstation 3100 as these systems use a mechanically identical system module. The enclosure can accommodate two 3.5-inch drives, which are mounted on trays above the system module. The system module is located on the left of the enclosure and the power supply, which takes up a fourth of the space inside the enclosure, is located on the left.